{"id":2216,"date":"2024-08-07T17:00:09","date_gmt":"2024-08-07T17:00:09","guid":{"rendered":"https:\/\/itnotes.apjsoftwares.in\/?p=2216"},"modified":"2024-08-07T17:46:55","modified_gmt":"2024-08-07T17:46:55","slug":"java-programming-interview-questions-for-4-years","status":"publish","type":"post","link":"https:\/\/itnotes.apjsoftwares.in\/index.php\/2024\/08\/07\/java-programming-interview-questions-for-4-years\/","title":{"rendered":"Java programming interview questions for 4 years"},"content":{"rendered":"\n

1. FizzBuzz Problem<\/h3>\n\n\n\n

Question:<\/strong> Write a Java program that prints the numbers from 1 to 100. But for multiples of three, print “Fizz” instead of the number and for the multiples of five, print “Buzz”. For numbers which are multiples of both three and five, print “FizzBuzz”.<\/p>\n\n\n\n

public class FizzBuzz {\n    public static void main(String[] args) {\n        for (int i = 1; i <= 100; i++) {\n            if (i % 3 == 0 && i % 5 == 0) {\n                System.out.println(\"FizzBuzz\");\n            } else if (i % 3 == 0) {\n                System.out.println(\"Fizz\");\n            } else if (i % 5 == 0) {\n                System.out.println(\"Buzz\");\n            } else {\n                System.out.println(i);\n            }\n        }\n    }\n}\n<\/code><\/pre>\n\n\n\n
2. Reverse a String<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to reverse a string without using the built-in reverse method.<\/p>\n\n\n\n
public class ReverseString {\n    public static void main(String[] args) {\n        String str = \"Hello, World!\";\n        String reversed = reverse(str);\n        System.out.println(reversed);\n    }\n\n    public static String reverse(String str) {\n        if (str == null || str.length() == 0) {\n            return str;\n        }\n        StringBuilder sb = new StringBuilder();\n        for (int i = str.length() - 1; i >= 0; i--) {\n            sb.append(str.charAt(i));\n        }\n        return sb.toString();\n    }\n}\n<\/code><\/pre>\n\n\n\n
3. Check for Palindrome<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to check if a given string is a palindrome.<\/p>\n\n\n\n
public class Palindrome {\n    public static void main(String[] args) {\n        String str = \"madam\";\n        boolean isPalindrome = isPalindrome(str);\n        System.out.println(str + \" is palindrome? \" + isPalindrome);\n    }\n\n    public static boolean isPalindrome(String str) {\n        int left = 0;\n        int right = str.length() - 1;\n        while (left < right) {\n            if (str.charAt(left) != str.charAt(right)) {\n                return false;\n            }\n            left++;\n            right--;\n        }\n        return true;\n    }\n}\n<\/code><\/pre>\n\n\n\n
4. Find the Missing Number<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to find the missing number in an array of size n<\/code> containing numbers from 1 to n<\/code>.<\/p>\n\n\n\n
public class MissingNumber {\n    public static void main(String[] args) {\n        int[] arr = {1, 2, 4, 5, 6};\n        int missingNumber = findMissingNumber(arr);\n        System.out.println(\"Missing number is: \" + missingNumber);\n    }\n\n    public static int findMissingNumber(int[] arr) {\n        int n = arr.length + 1;\n        int sum = (n * (n + 1)) \/ 2;\n        int arrSum = 0;\n        for (int num : arr) {\n            arrSum += num;\n        }\n        return sum - arrSum;\n    }\n}\n<\/code><\/pre>\n\n\n\n
5. Fibonacci Series<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to print the first n<\/code> Fibonacci numbers.<\/p>\n\n\n\n
public class Fibonacci {\n    public static void main(String[] args) {\n        int n = 10;\n        printFibonacci(n);\n    }\n\n    public static void printFibonacci(int n) {\n        int a = 0, b = 1;\n        System.out.print(a + \" \" + b);\n        for (int i = 2; i < n; i++) {\n            int next = a + b;\n            System.out.print(\" \" + next);\n            a = b;\n            b = next;\n        }\n    }\n}\n<\/code><\/pre>\n\n\n\n
6. Anagram Check<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to check if two strings are anagrams of each other.<\/p>\n\n\n\n
import java.util.Arrays;\n\npublic class AnagramCheck {\n    public static void main(String[] args) {\n        String str1 = \"listen\";\n        String str2 = \"silent\";\n        boolean isAnagram = areAnagrams(str1, str2);\n        System.out.println(str1 + \" and \" + str2 + \" are anagrams? \" + isAnagram);\n    }\n\n    public static boolean areAnagrams(String str1, String str2) {\n        if (str1.length() != str2.length()) {\n            return false;\n        }\n        char[] charArray1 = str1.toCharArray();\n        char[] charArray2 = str2.toCharArray();\n        Arrays.sort(charArray1);\n        Arrays.sort(charArray2);\n        return Arrays.equals(charArray1, charArray2);\n    }\n}\n<\/code><\/pre>\n\n\n\n
7. Factorial Calculation<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to calculate the factorial of a number using recursion.<\/p>\n\n\n\n
public class Factorial {\n    public static void main(String[] args) {\n        int number = 5;\n        int result = factorial(number);\n        System.out.println(\"Factorial of \" + number + \" is: \" + result);\n    }\n\n    public static int factorial(int n) {\n        if (n == 0) {\n            return 1;\n        }\n        return n * factorial(n - 1);\n    }\n}\n<\/code><\/pre>\n\n\n\n
8. Find the Second Largest Number in an Array<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to find the second largest number in an array.<\/p>\n\n\n\n
public class SecondLargest {\n    public static void main(String[] args) {\n        int[] arr = {10, 5, 20, 8, 12};\n        int secondLargest = findSecondLargest(arr);\n        System.out.println(\"Second largest number is: \" + secondLargest);\n    }\n\n    public static int findSecondLargest(int[] arr) {\n        int firstLargest = Integer.MIN_VALUE;\n        int secondLargest = Integer.MIN_VALUE;\n        for (int num : arr) {\n            if (num > firstLargest) {\n                secondLargest = firstLargest;\n                firstLargest = num;\n            } else if (num > secondLargest && num != firstLargest) {\n                secondLargest = num;\n            }\n        }\n        return secondLargest;\n    }\n}\n<\/code><\/pre>\n\n\n\n
9. Sum of Digits in a Number<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to find the sum of the digits of a given number.<\/p>\n\n\n\n
public class SumOfDigits {\n    public static void main(String[] args) {\n        int number = 12345;\n        int sum = sumOfDigits(number);\n        System.out.println(\"Sum of digits of \" + number + \" is: \" + sum);\n    }\n\n    public static int sumOfDigits(int number) {\n        int sum = 0;\n        while (number != 0) {\n            sum += number % 10;\n            number \/= 10;\n        }\n        return sum;\n    }\n}\n<\/code><\/pre>\n\n\n\n
10. Print All Permutations of a String<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to print all permutations of a given string.<\/p>\n\n\n\n
public class Permutations {\n    public static void main(String[] args) {\n        String str = \"ABC\";\n        permute(str, 0, str.length() - 1);\n    }\n\n    public static void permute(String str, int l, int r) {\n        if (l == r) {\n            System.out.println(str);\n        } else {\n            for (int i = l; i <= r; i++) {\n                str = swap(str, l, i);\n                permute(str, l + 1, r);\n                str = swap(str, l, i); \/\/ backtrack\n            }\n        }\n    }\n\n    public static String swap(String str, int i, int j) {\n        char[] charArray = str.toCharArray();\n        char temp = charArray[i];\n        charArray[i] = charArray[j];\n        charArray[j] = temp;\n        return String.valueOf(charArray);\n    }\n}\n<\/code><\/pre>\n\n\n\n
Collection Programs<\/h2>\n\n\n\n
1. Write a Java program to demonstrate the use of ArrayList<\/code>.<\/strong><\/p>\n\n\n\n
import java.util.ArrayList;\nimport java.util.List;\n\npublic class ArrayListExample {\n    public static void main(String[] args) {\n        List<String> fruits = new ArrayList<>();\n\n        \/\/ Adding elements\n        fruits.add(\"Apple\");\n        fruits.add(\"Banana\");\n        fruits.add(\"Orange\");\n\n        \/\/ Iterating through the list\n        for (String fruit : fruits) {\n            System.out.println(fruit);\n        }\n\n        \/\/ Getting an element\n        System.out.println(\"First fruit: \" + fruits.get(0));\n\n        \/\/ Removing an element\n        fruits.remove(\"Banana\");\n        System.out.println(\"After removing Banana: \" + fruits);\n\n        \/\/ Checking size\n        System.out.println(\"Size of the list: \" + fruits.size());\n    }\n}\n<\/code><\/pre>\n\n\n\n
2. Write a Java program to demonstrate the use of LinkedList<\/code>.<\/strong><\/p>\n\n\n\n
import java.util.LinkedList;\n\npublic class LinkedListExample {\n    public static void main(String[] args) {\n        LinkedList<String> animals = new LinkedList<>();\n\n        \/\/ Adding elements\n        animals.add(\"Dog\");\n        animals.add(\"Cat\");\n        animals.add(\"Horse\");\n\n        \/\/ Iterating through the list\n        for (String animal : animals) {\n            System.out.println(animal);\n        }\n\n        \/\/ Adding elements at the beginning and end\n        animals.addFirst(\"Elephant\");\n        animals.addLast(\"Zebra\");\n        System.out.println(\"After adding elements at beginning and end: \" + animals);\n\n        \/\/ Removing first and last elements\n        animals.removeFirst();\n        animals.removeLast();\n        System.out.println(\"After removing first and last elements: \" + animals);\n\n        \/\/ Checking size\n        System.out.println(\"Size of the list: \" + animals.size());\n    }\n}\n<\/code><\/pre>\n\n\n\n
3. Write a Java program to demonstrate the use of HashSet<\/code>.<\/strong><\/p>\n\n\n\n
import java.util.HashSet;\nimport java.util.Set;\n\npublic class HashSetExample {\n    public static void main(String[] args) {\n        Set<String> countries = new HashSet<>();\n\n        \/\/ Adding elements\n        countries.add(\"USA\");\n        countries.add(\"Canada\");\n        countries.add(\"Mexico\");\n\n        \/\/ Attempting to add a duplicate element\n        countries.add(\"USA\");\n\n        \/\/ Iterating through the set\n        for (String country : countries) {\n            System.out.println(country);\n        }\n\n        \/\/ Checking if an element exists\n        System.out.println(\"Contains Canada? \" + countries.contains(\"Canada\"));\n\n        \/\/ Removing an element\n        countries.remove(\"Mexico\");\n        System.out.println(\"After removing Mexico: \" + countries);\n\n        \/\/ Checking size\n        System.out.println(\"Size of the set: \" + countries.size());\n    }\n}\n<\/code><\/pre>\n\n\n\n
4. Write a Java program to demonstrate the use of TreeSet<\/code>.<\/strong><\/p>\n\n\n\n
import java.util.TreeSet;\n\npublic class TreeSetExample {\n    public static void main(String[] args) {\n        TreeSet<Integer> numbers = new TreeSet<>();\n\n        \/\/ Adding elements\n        numbers.add(10);\n        numbers.add(5);\n        numbers.add(15);\n\n        \/\/ Iterating through the set\n        for (Integer number : numbers) {\n            System.out.println(number);\n        }\n\n        \/\/ Getting the first and last elements\n        System.out.println(\"First element: \" + numbers.first());\n        System.out.println(\"Last element: \" + numbers.last());\n\n        \/\/ Removing an element\n        numbers.remove(10);\n        System.out.println(\"After removing 10: \" + numbers);\n\n        \/\/ Checking size\n        System.out.println(\"Size of the set: \" + numbers.size());\n    }\n}\n<\/code><\/pre>\n\n\n\n
5. Write a Java program to demonstrate the use of HashMap<\/code>.<\/strong><\/p>\n\n\n\n
import java.util.HashMap;\nimport java.util.Map;\n\npublic class HashMapExample {\n    public static void main(String[] args) {\n        Map<String, Integer> ages = new HashMap<>();\n\n        \/\/ Adding elements\n        ages.put(\"Alice\", 30);\n        ages.put(\"Bob\", 25);\n        ages.put(\"Charlie\", 35);\n\n        \/\/ Iterating through the map\n        for (Map.Entry<String, Integer> entry : ages.entrySet()) {\n            System.out.println(entry.getKey() + \": \" + entry.getValue());\n        }\n\n        \/\/ Getting an element\n        System.out.println(\"Alice's age: \" + ages.get(\"Alice\"));\n\n        \/\/ Removing an element\n        ages.remove(\"Bob\");\n        System.out.println(\"After removing Bob: \" + ages);\n\n        \/\/ Checking size\n        System.out.println(\"Size of the map: \" + ages.size());\n    }\n}\n<\/code><\/pre>\n\n\n\n
6. Write a Java program to demonstrate the use of TreeMap<\/code>.<\/strong><\/p>\n\n\n\n
import java.util.Map;\nimport java.util.TreeMap;\n\npublic class TreeMapExample {\n    public static void main(String[] args) {\n        TreeMap<String, Integer> scores = new TreeMap<>();\n\n        \/\/ Adding elements\n        scores.put(\"Alice\", 85);\n        scores.put(\"Bob\", 90);\n        scores.put(\"Charlie\", 80);\n\n        \/\/ Iterating through the map\n        for (Map.Entry<String, Integer> entry : scores.entrySet()) {\n            System.out.println(entry.getKey() + \": \" + entry.getValue());\n        }\n\n        \/\/ Getting the first and last entries\n        System.out.println(\"First entry: \" + scores.firstEntry());\n        System.out.println(\"Last entry: \" + scores.lastEntry());\n\n        \/\/ Removing an element\n        scores.remove(\"Bob\");\n        System.out.println(\"After removing Bob: \" + scores);\n\n        \/\/ Checking size\n        System.out.println(\"Size of the map: \" + scores.size());\n    }\n}\n<\/code><\/pre>\n\n\n\n
7. Write a Java program to demonstrate the use of PriorityQueue<\/code>.<\/strong><\/p>\n\n\n\n
import java.util.PriorityQueue;\n\npublic class PriorityQueueExample {\n    public static void main(String[] args) {\n        PriorityQueue<Integer> queue = new PriorityQueue<>();\n\n        \/\/ Adding elements\n        queue.add(10);\n        queue.add(5);\n        queue.add(15);\n\n        \/\/ Iterating through the queue\n        while (!queue.isEmpty()) {\n            System.out.println(queue.poll());\n        }\n    }\n}\n<\/code><\/pre>\n\n\n\n
8. Write a Java program to demonstrate the use of Stack<\/code><\/strong><\/p>\n\n\n\n
import java.util.Stack;\n\npublic class StackExample {\n    public static void main(String[] args) {\n        Stack<String> stack = new Stack<>();\n\n        \/\/ Pushing elements onto the stack\n        stack.push(\"Apple\");\n        stack.push(\"Banana\");\n        stack.push(\"Cherry\");\n\n        \/\/ Popping elements from the stack\n        while (!stack.isEmpty()) {\n            System.out.println(stack.pop());\n        }\n    }\n}\n<\/code><\/pre>\n\n\n\n
9. Write a Java program to demonstrate the use of Queue<\/code> implemented using LinkedList<\/code>.<\/strong><\/p>\n\n\n\n
import java.util.LinkedList;\nimport java.util.Queue;\n\npublic class QueueExample {\n    public static void main(String[] args) {\n        Queue<String> queue = new LinkedList<>();\n\n        \/\/ Adding elements\n        queue.add(\"Apple\");\n        queue.add(\"Banana\");\n        queue.add(\"Cherry\");\n\n        \/\/ Polling elements from the queue\n        while (!queue.isEmpty()) {\n            System.out.println(queue.poll());\n        }\n    }\n}\n<\/code><\/pre>\n\n\n\n
10. Write a Java program to demonstrate the use of Deque<\/code> implemented using ArrayDeque<\/code><\/strong><\/p>\n\n\n\n
import java.util.ArrayDeque;\nimport java.util.Deque;\n\npublic class DequeExample {\n    public static void main(String[] args) {\n        Deque<String> deque = new ArrayDeque<>();\n\n        \/\/ Adding elements to both ends\n        deque.addFirst(\"Apple\");\n        deque.addLast(\"Banana\");\n        deque.addFirst(\"Cherry\");\n\n        \/\/ Iterating through the deque\n        while (!deque.isEmpty()) {\n            System.out.println(deque.pollFirst());\n        }\n    }\n}\n<\/code><\/pre>\n\n\n\n
Java 8 Features<\/h2>\n\n\n\n
1. Lambda Expressions<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate the use of lambda expressions.<\/p>\n\n\n\n
import java.util.Arrays;\nimport java.util.List;\n\npublic class LambdaExample {\n    public static void main(String[] args) {\n        List<String> names = Arrays.asList(\"Alice\", \"Bob\", \"Charlie\");\n\n        \/\/ Using lambda expression to iterate through the list\n        names.forEach(name -> System.out.println(name));\n    }\n}\n<\/code><\/pre>\n\n\n\n
2. Functional Interfaces<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate the use of functional interfaces.<\/p>\n\n\n\n
import java.util.function.Predicate;\n\npublic class FunctionalInterfaceExample {\n    public static void main(String[] args) {\n        Predicate<Integer> isEven = number -> number % 2 == 0;\n\n        System.out.println(\"Is 4 even? \" + isEven.test(4));\n        System.out.println(\"Is 5 even? \" + isEven.test(5));\n    }\n}\n<\/code><\/pre>\n\n\n\n
3. Streams API<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate the use of the Streams API.<\/p>\n\n\n\n
import java.util.Arrays;\nimport java.util.List;\nimport java.util.stream.Collectors;\n\npublic class StreamsExample {\n    public static void main(String[] args) {\n        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);\n\n        \/\/ Using Streams API to filter even numbers and collect them into a list\n        List<Integer> evenNumbers = numbers.stream()\n                                           .filter(number -> number % 2 == 0)\n                                           .collect(Collectors.toList());\n\n        System.out.println(\"Even numbers: \" + evenNumbers);\n    }\n}\n<\/code><\/pre>\n\n\n\n
4. Optional Class<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate the use of the Optional<\/code> class.<\/p>\n\n\n\n
import java.util.Optional;\n\npublic class OptionalExample {\n    public static void main(String[] args) {\n        String[] words = new String[10];\n        words[2] = \"hello\";\n\n        Optional<String> checkNull = Optional.ofNullable(words[2]);\n        checkNull.ifPresent(System.out::println);\n\n        \/\/ Using Optional to handle a potential null value\n        Optional<String> word = Optional.ofNullable(words[5]);\n        String result = word.orElse(\"Default value\");\n        System.out.println(result);\n    }\n}\n<\/code><\/pre>\n\n\n\n
5. Method References<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate the use of method references.<\/p>\n\n\n\n
import java.util.Arrays;\nimport java.util.List;\n\npublic class MethodReferenceExample {\n    public static void main(String[] args) {\n        List<String> names = Arrays.asList(\"Alice\", \"Bob\", \"Charlie\");\n\n        \/\/ Using method reference to iterate through the list\n        names.forEach(System.out::println);\n    }\n}\n<\/code><\/pre>\n\n\n\n
6. Default Methods in Interfaces<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate default methods in interfaces.<\/p>\n\n\n\n
interface Vehicle {\n    default void print() {\n        System.out.println(\"I am a vehicle.\");\n    }\n\n    static void blowHorn() {\n        System.out.println(\"Blowing horn!!!\");\n    }\n}\n\nclass Car implements Vehicle {\n    @Override\n    public void print() {\n        System.out.println(\"I am a car.\");\n    }\n}\n\npublic class DefaultMethodsExample {\n    public static void main(String[] args) {\n        Vehicle car = new Car();\n        car.print(); \/\/ Calls the overridden method in Car\n        Vehicle.blowHorn(); \/\/ Calls the static method in Vehicle interface\n    }\n}\n<\/code><\/pre>\n\n\n\n
7. New Date and Time API<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate the new Date and Time API.<\/p>\n\n\n\n
import java.time.LocalDate;\nimport java.time.LocalDateTime;\nimport java.time.LocalTime;\nimport java.time.format.DateTimeFormatter;\n\npublic class DateTimeExample {\n    public static void main(String[] args) {\n        LocalDate date = LocalDate.now();\n        System.out.println(\"Current Date: \" + date);\n\n        LocalTime time = LocalTime.now();\n        System.out.println(\"Current Time: \" + time);\n\n        LocalDateTime dateTime = LocalDateTime.now();\n        System.out.println(\"Current DateTime: \" + dateTime);\n\n        \/\/ Formatting DateTime\n        DateTimeFormatter formatter = DateTimeFormatter.ofPattern(\"dd-MM-yyyy HH:mm:ss\");\n        String formattedDateTime = dateTime.format(formatter);\n        System.out.println(\"Formatted DateTime: \" + formattedDateTime);\n    }\n}\n<\/code><\/pre>\n\n\n\n
8. Stream Reduction<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate stream reduction.<\/p>\n\n\n\n
import java.util.Arrays;\nimport java.util.List;\n\npublic class StreamReductionExample {\n    public static void main(String[] args) {\n        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);\n\n        \/\/ Using reduce() to calculate the sum of the list\n        int sum = numbers.stream()\n                         .reduce(0, (a, b) -> a + b);\n\n        System.out.println(\"Sum: \" + sum);\n\n        \/\/ Using method reference with reduce()\n        int product = numbers.stream()\n                             .reduce(1, Math::multiplyExact);\n\n        System.out.println(\"Product: \" + product);\n    }\n}\n<\/code><\/pre>\n\n\n\n
9. Parallel Streams<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate parallel streams.<\/p>\n\n\n\n
import java.util.Arrays;\nimport java.util.List;\n\npublic class ParallelStreamsExample {\n    public static void main(String[] args) {\n        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);\n\n        \/\/ Using parallel stream to filter even numbers\n        List<Integer> evenNumbers = numbers.parallelStream()\n                                           .filter(number -> number % 2 == 0)\n                                           .collect(Collectors.toList());\n\n        System.out.println(\"Even numbers: \" + evenNumbers);\n    }\n}\n<\/code><\/pre>\n\n\n\n
10. Collectors<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate the use of Collectors<\/code>.<\/p>\n\n\n\n
import java.util.Arrays;\nimport java.util.List;\nimport java.util.Map;\nimport java.util.stream.Collectors;\n\npublic class CollectorsExample {\n    public static void main(String[] args) {\n        List<String> names = Arrays.asList(\"Alice\", \"Bob\", \"Charlie\", \"David\", \"Edward\");\n\n        \/\/ Using Collectors to group names by their starting letter\n        Map<Character, List<String>> groupedByFirstLetter = names.stream()\n                .collect(Collectors.groupingBy(name -> name.charAt(0)));\n\n        groupedByFirstLetter.forEach((letter, group) -> {\n            System.out.println(letter + \": \" + group);\n        });\n    }\n}\n<\/code><\/pre>\n\n\n\n
11. Stream Operations: map()<\/code><\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate the use of the map()<\/code> method in streams.<\/p>\n\n\n\n
import java.util.Arrays;\nimport java.util.List;\nimport java.util.stream.Collectors;\n\npublic class StreamMapExample {\n    public static void main(String[] args) {\n        List<String> names = Arrays.asList(\"alice\", \"bob\", \"charlie\");\n\n        \/\/ Using map() to convert all names to uppercase\n        List<String> upperCaseNames = names.stream()\n                                           .map(String::toUpperCase)\n                                           .collect(Collectors.toList());\n\n        System.out.println(upperCaseNames);\n    }\n}\n<\/code><\/pre>\n\n\n\n
12. Stream Operations: flatMap()<\/code><\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate the use of the flatMap()<\/code> method in streams.<\/p>\n\n\n\n
import java.util.Arrays;\nimport java.util.List;\nimport java.util.stream.Collectors;\n\npublic class StreamFlatMapExample {\n    public static void main(String[] args) {\n        List<List<String>> namesList = Arrays.asList(\n            Arrays.asList(\"Alice\", \"Bob\"),\n            Arrays.asList(\"Charlie\", \"David\"),\n            Arrays.asList(\"Edward\", \"Frank\")\n        );\n\n        \/\/ Using flatMap() to flatten the list of lists into a single list\n        List<String> flatList = namesList.stream()\n                                         .flatMap(List::stream)\n                                         .collect(Collectors.toList());\n\n        System.out.println(flatList);\n    }\n}\n<\/code><\/pre>\n\n\n\n
13. Stream Operations: sorted()<\/code><\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate the use of the sorted()<\/code> method in streams.<\/p>\n\n\n\n
import java.util.Arrays;\nimport java.util.List;\n\npublic class StreamSortedExample {\n    public static void main(String[] args) {\n        List<Integer> numbers = Arrays.asList(5, 3, 9, 1, 4, 2);\n\n        \/\/ Using sorted() to sort the list in natural order\n        List<Integer> sortedNumbers = numbers.stream()\n                                             .sorted()\n                                             .collect(Collectors.toList());\n\n        System.out.println(sortedNumbers);\n    }\n}\n<\/code><\/pre>\n\n\n\n
14. Stream Operations: distinct()<\/code><\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate the use of the distinct()<\/code> method in streams.<\/p>\n\n\n\n
import java.util.Arrays;\nimport java.util.List;\n\npublic class StreamDistinctExample {\n    public static void main(String[] args) {\n        List<Integer> numbers = Arrays.asList(1, 2, 3, 2, 4, 5, 1, 6);\n\n        \/\/ Using distinct() to remove duplicates from the list\n        List<Integer> distinctNumbers = numbers.stream()\n                                               .distinct()\n                                               .collect(Collectors.toList());\n\n        System.out.println(distinctNumbers);\n    }\n}\n<\/code><\/pre>\n\n\n\n
15. Stream Operations: peek()<\/code><\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate the use of the peek()<\/code> method in streams.<\/p>\n\n\n\n
import java.util.Arrays;\nimport java.util.List;\n\npublic class StreamPeekExample {\n    public static void main(String[] args) {\n        List<String> names = Arrays.asList(\"Alice\", \"Bob\", \"Charlie\");\n\n        \/\/ Using peek() to log the elements during the stream processing\n        List<String> processedNames = names.stream()\n                                           .peek(name -> System.out.println(\"Processing: \" + name))\n                                           .map(String::toUpperCase)\n                                           .collect(Collectors.toList());\n\n        System.out.println(processedNames);\n    }\n}\n<\/code><\/pre>\n\n\n\n
16. Stream Operations: count()<\/code><\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate the use of the count()<\/code> method in streams.<\/p>\n\n\n\n
import java.util.Arrays;\nimport java.util.List;\n\npublic class StreamCountExample {\n    public static void main(String[] args) {\n        List<String> names = Arrays.asList(\"Alice\", \"Bob\", \"Charlie\", \"David\", \"Edward\");\n\n        \/\/ Using count() to count the number of elements in the stream\n        long count = names.stream()\n                          .filter(name -> name.length() > 3)\n                          .count();\n\n        System.out.println(\"Number of names longer than 3 characters: \" + count);\n    }\n}\n<\/code><\/pre>\n\n\n\n
17. Stream Operations: findFirst()<\/code><\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate the use of the findFirst()<\/code> method in streams.<\/p>\n\n\n\n
import java.util.Arrays;\nimport java.util.List;\n\npublic class StreamFindFirstExample {\n    public static void main(String[] args) {\n        List<String> names = Arrays.asList(\"Alice\", \"Bob\", \"Charlie\");\n\n        \/\/ Using findFirst() to find the first element in the stream\n        String firstElement = names.stream()\n                                   .findFirst()\n                                   .orElse(\"No elements\");\n\n        System.out.println(\"First element: \" + firstElement);\n    }\n}\n<\/code><\/pre>\n\n\n\n
18. Stream Operations: reduce()<\/code><\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate the use of the reduce()<\/code> method in streams.<\/p>\n\n\n\n
import java.util.Arrays;\nimport java.util.List;\n\npublic class StreamReduceExample {\n    public static void main(String[] args) {\n        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);\n\n        \/\/ Using reduce() to calculate the sum of all elements in the list\n        int sum = numbers.stream()\n                         .reduce(0, (a, b) -> a + b);\n\n        System.out.println(\"Sum: \" + sum);\n\n        \/\/ Using method reference with reduce()\n        int product = numbers.stream()\n                             .reduce(1, Math::multiplyExact);\n\n        System.out.println(\"Product: \" + product);\n    }\n}\n<\/code><\/pre>\n\n\n\n
19. Stream Operations: collect()<\/code><\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate the use of the collect()<\/code> method in streams.<\/p>\n\n\n\n
import java.util.Arrays;\nimport java.util.List;\nimport java.util.stream.Collectors;\n\npublic class StreamCollectExample {\n    public static void main(String[] args) {\n        List<String> names = Arrays.asList(\"Alice\", \"Bob\", \"Charlie\");\n\n        \/\/ Using collect() to convert the stream into a list\n        List<String> upperCaseNames = names.stream()\n                                           .map(String::toUpperCase)\n                                           .collect(Collectors.toList());\n\n        System.out.println(upperCaseNames);\n    }\n}\n<\/code><\/pre>\n\n\n\n
20. Stream Operations: groupingBy()<\/code><\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate the use of the groupingBy()<\/code> method in streams.<\/p>\n\n\n\n
import java.util.Arrays;\nimport java.util.List;\nimport java.util.Map;\nimport java.util.stream.Collectors;\n\npublic class StreamGroupingByExample {\n    public static void main(String[] args) {\n        List<String> names = Arrays.asList(\"Alice\", \"Bob\", \"Charlie\", \"David\", \"Edward\");\n\n        \/\/ Using groupingBy() to group names by their starting letter\n        Map<Character, List<String>> groupedByFirstLetter = names.stream()\n                .collect(Collectors.groupingBy(name -> name.charAt(0)));\n\n        groupedByFirstLetter.forEach((letter, group) -> {\n            System.out.println(letter + \": \" + group);\n        });\n    }\n}\n<\/code><\/pre>\n\n\n\n
JDBC programs in Java<\/h2>\n\n\n\n
1. Connect to a Database<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate connecting to a database using JDBC<\/p>\n\n\n\n
import java.sql.Connection;\nimport java.sql.DriverManager;\nimport java.sql.SQLException;\n\npublic class JdbcConnectExample {\n    public static void main(String[] args) {\n        String url = \"jdbc:mysql:\/\/localhost:3306\/mydatabase\";\n        String username = \"root\";\n        String password = \"password\";\n\n        try (Connection connection = DriverManager.getConnection(url, username, password)) {\n            if (connection != null) {\n                System.out.println(\"Connected to the database!\");\n            } else {\n                System.out.println(\"Failed to connect to the database.\");\n            }\n        } catch (SQLException e) {\n            e.printStackTrace();\n        }\n    }\n}\n<\/code><\/pre>\n\n\n\n
2. Create a Table<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to create a table using JDBC.<\/p>\n\n\n\n
import java.sql.Connection;\nimport java.sql.DriverManager;\nimport java.sql.SQLException;\nimport java.sql.Statement;\n\npublic class JdbcCreateTableExample {\n    public static void main(String[] args) {\n        String url = \"jdbc:mysql:\/\/localhost:3306\/mydatabase\";\n        String username = \"root\";\n        String password = \"password\";\n\n        String createTableSQL = \"CREATE TABLE IF NOT EXISTS users (\"\n                + \"id INT AUTO_INCREMENT PRIMARY KEY, \"\n                + \"name VARCHAR(100) NOT NULL, \"\n                + \"email VARCHAR(100) NOT NULL UNIQUE, \"\n                + \"created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP)\";\n\n        try (Connection connection = DriverManager.getConnection(url, username, password);\n             Statement statement = connection.createStatement()) {\n\n            statement.execute(createTableSQL);\n            System.out.println(\"Table 'users' created successfully.\");\n        } catch (SQLException e) {\n            e.printStackTrace();\n        }\n    }\n}\n<\/code><\/pre>\n\n\n\n
3. Insert Data into a Table<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to insert data into a table using JDBC.<\/p>\n\n\n\n
import java.sql.Connection;\nimport java.sql.DriverManager;\nimport java.sql.PreparedStatement;\nimport java.sql.SQLException;\n\npublic class JdbcInsertExample {\n    public static void main(String[] args) {\n        String url = \"jdbc:mysql:\/\/localhost:3306\/mydatabase\";\n        String username = \"root\";\n        String password = \"password\";\n\n        String insertSQL = \"INSERT INTO users (name, email) VALUES (?, ?)\";\n\n        try (Connection connection = DriverManager.getConnection(url, username, password);\n             PreparedStatement preparedStatement = connection.prepareStatement(insertSQL)) {\n\n            preparedStatement.setString(1, \"John Doe\");\n            preparedStatement.setString(2, \"john.doe@example.com\");\n\n            int row = preparedStatement.executeUpdate();\n            System.out.println(row + \" row(s) inserted.\");\n        } catch (SQLException e) {\n            e.printStackTrace();\n        }\n    }\n}\n<\/code><\/pre>\n\n\n\n
4. Retrieve Data from a Table<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to retrieve data from a table using JDBC.<\/p>\n\n\n\n
import java.sql.Connection;\nimport java.sql.DriverManager;\nimport java.sql.ResultSet;\nimport java.sql.SQLException;\nimport java.sql.Statement;\n\npublic class JdbcSelectExample {\n    public static void main(String[] args) {\n        String url = \"jdbc:mysql:\/\/localhost:3306\/mydatabase\";\n        String username = \"root\";\n        String password = \"password\";\n\n        String selectSQL = \"SELECT * FROM users\";\n\n        try (Connection connection = DriverManager.getConnection(url, username, password);\n             Statement statement = connection.createStatement();\n             ResultSet resultSet = statement.executeQuery(selectSQL)) {\n\n            while (resultSet.next()) {\n                int id = resultSet.getInt(\"id\");\n                String name = resultSet.getString(\"name\");\n                String email = resultSet.getString(\"email\");\n                System.out.println(\"ID: \" + id + \", Name: \" + name + \", Email: \" + email);\n            }\n        } catch (SQLException e) {\n            e.printStackTrace();\n        }\n    }\n}\n<\/code><\/pre>\n\n\n\n
5. Update Data in a Table<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to update data in a table using JDBC.<\/p>\n\n\n\n
import java.sql.Connection;\nimport java.sql.DriverManager;\nimport java.sql.PreparedStatement;\nimport java.sql.SQLException;\n\npublic class JdbcUpdateExample {\n    public static void main(String[] args) {\n        String url = \"jdbc:mysql:\/\/localhost:3306\/mydatabase\";\n        String username = \"root\";\n        String password = \"password\";\n\n        String updateSQL = \"UPDATE users SET email = ? WHERE name = ?\";\n\n        try (Connection connection = DriverManager.getConnection(url, username, password);\n             PreparedStatement preparedStatement = connection.prepareStatement(updateSQL)) {\n\n            preparedStatement.setString(1, \"new.email@example.com\");\n            preparedStatement.setString(2, \"John Doe\");\n\n            int row = preparedStatement.executeUpdate();\n            System.out.println(row + \" row(s) updated.\");\n        } catch (SQLException e) {\n            e.printStackTrace();\n        }\n    }\n}\n<\/code><\/pre>\n\n\n\n
6. Delete Data from a Table<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to delete data from a table using JDBC.<\/p>\n\n\n\n
import java.sql.Connection;\nimport java.sql.DriverManager;\nimport java.sql.PreparedStatement;\nimport java.sql.SQLException;\n\npublic class JdbcDeleteExample {\n    public static void main(String[] args) {\n        String url = \"jdbc:mysql:\/\/localhost:3306\/mydatabase\";\n        String username = \"root\";\n        String password = \"password\";\n\n        String deleteSQL = \"DELETE FROM users WHERE name = ?\";\n\n        try (Connection connection = DriverManager.getConnection(url, username, password);\n             PreparedStatement preparedStatement = connection.prepareStatement(deleteSQL)) {\n\n            preparedStatement.setString(1, \"John Doe\");\n\n            int row = preparedStatement.executeUpdate();\n            System.out.println(row + \" row(s) deleted.\");\n        } catch (SQLException e) {\n            e.printStackTrace();\n        }\n    }\n}\n<\/code><\/pre>\n\n\n\n
7. Handling Transactions<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate transaction handling using JDBC.<\/p>\n\n\n\n
import java.sql.Connection;\nimport java.sql.DriverManager;\nimport java.sql.PreparedStatement;\nimport java.sql.SQLException;\n\npublic class JdbcTransactionExample {\n    public static void main(String[] args) {\n        String url = \"jdbc:mysql:\/\/localhost:3306\/mydatabase\";\n        String username = \"root\";\n        String password = \"password\";\n\n        String insertSQL1 = \"INSERT INTO users (name, email) VALUES (?, ?)\";\n        String insertSQL2 = \"INSERT INTO users (name, email) VALUES (?, ?)\";\n\n        try (Connection connection = DriverManager.getConnection(url, username, password)) {\n            connection.setAutoCommit(false);\n\n            try (PreparedStatement preparedStatement1 = connection.prepareStatement(insertSQL1);\n                 PreparedStatement preparedStatement2 = connection.prepareStatement(insertSQL2)) {\n\n                preparedStatement1.setString(1, \"Alice\");\n                preparedStatement1.setString(2, \"alice@example.com\");\n                preparedStatement1.executeUpdate();\n\n                preparedStatement2.setString(1, \"Bob\");\n                preparedStatement2.setString(2, \"bob@example.com\");\n                preparedStatement2.executeUpdate();\n\n                connection.commit();\n                System.out.println(\"Transaction committed successfully.\");\n            } catch (SQLException e) {\n                connection.rollback();\n                System.out.println(\"Transaction rolled back.\");\n                e.printStackTrace();\n            }\n        } catch (SQLException e) {\n            e.printStackTrace();\n        }\n    }\n}\n<\/code><\/pre>\n\n\n\n
8. Batch Processing<\/h3>\n\n\n\n
Question:<\/strong> Write a Java program to demonstrate batch processing using JDBC.<\/p>\n\n\n\n
import java.sql.Connection;\nimport java.sql.DriverManager;\nimport java.sql.PreparedStatement;\nimport java.sql.SQLException;\n\npublic class JdbcBatchExample {\n    public static void main(String[] args) {\n        String url = \"jdbc:mysql:\/\/localhost:3306\/mydatabase\";\n        String username = \"root\";\n        String password = \"password\";\n\n        String insertSQL = \"INSERT INTO users (name, email) VALUES (?, ?)\";\n\n        try (Connection connection = DriverManager.getConnection(url, username, password);\n             PreparedStatement preparedStatement = connection.prepareStatement(insertSQL)) {\n\n            connection.setAutoCommit(false);\n\n            preparedStatement.setString(1, \"User1\");\n            preparedStatement.setString(2, \"user1@example.com\");\n            preparedStatement.addBatch();\n\n            preparedStatement.setString(1, \"User2\");\n            preparedStatement.setString(2, \"user2@example.com\");\n            preparedStatement.addBatch();\n\n            preparedStatement.setString(1, \"User3\");\n            preparedStatement.setString(2, \"user3@example.com\");\n            preparedStatement.addBatch();\n\n            int[] updateCounts = preparedStatement.executeBatch();\n            connection.commit();\n            System.out.println(\"Batch executed successfully. \" + updateCounts.length + \" rows affected.\");\n        } catch (SQLException e) {\n            e.printStackTrace();\n        }\n    }\n}\n<\/code><\/pre>\n\n\n\n
Spring Boot MVC examples<\/h2>\n\n\n\n
1. Setting up a Spring Boot Application<\/h3>\n\n\n\n
Question:<\/strong> Write a simple Spring Boot application with an MVC controller.<\/p>\n\n\n\n
Answer:<\/strong> Step 1:<\/strong> Create a new Spring Boot project using Spring Initializr<\/a>. Add dependencies for Spring Web.<\/p>\n\n\n\n
Step 2:<\/strong> Create the main application class.<\/p>\n\n\n\n
import org.springframework.boot.SpringApplication;\nimport org.springframework.boot.autoconfigure.SpringBootApplication;\n\n@SpringBootApplication\npublic class SpringBootMvcExampleApplication {\n    public static void main(String[] args) {\n        SpringApplication.run(SpringBootMvcExampleApplication.class, args);\n    }\n}\n<\/code><\/pre>\n\n\n\n
Step 3:<\/strong> Create a simple MVC controller.<\/p>\n\n\n\n
import org.springframework.stereotype.Controller;\nimport org.springframework.ui.Model;\nimport org.springframework.web.bind.annotation.GetMapping;\n\n@Controller\npublic class HelloController {\n\n    @GetMapping(\"\/hello\")\n    public String hello(Model model) {\n        model.addAttribute(\"message\", \"Hello, Spring Boot MVC!\");\n        return \"hello\";\n    }\n}\n<\/code><\/pre>\n\n\n\n
Step 4:<\/strong> Create a Thymeleaf template (hello.html<\/code>) in src\/main\/resources\/templates<\/code>.<\/p>\n\n\n\n
<!DOCTYPE html>\n<html xmlns:th=\"http:\/\/www.thymeleaf.org\">\n<head>\n    <title>Hello Page<\/title>\n<\/head>\n<body>\n    <h1 th:text=\"${message}\"><\/h1>\n<\/body>\n<\/html>\n<\/code><\/pre>\n\n\n\n
<\/p>\n\n\n\n
2. Handling Form Submissions<\/h3>\n\n\n\n
Question:<\/strong> Write a Spring Boot MVC application to handle form submissions.<\/p>\n\n\n\n
Answer:<\/strong> Step 1:<\/strong> Create a form template (form.html<\/code>).<\/p>\n\n\n\n
<!DOCTYPE html>\n<html xmlns:th=\"http:\/\/www.thymeleaf.org\">\n<head>\n    <title>Form Page<\/title>\n<\/head>\n<body>\n    <form action=\"#\" th:action=\"@{\/submitForm}\" th:object=\"${user}\" method=\"post\">\n        <label for=\"name\">Name:<\/label>\n        <input type=\"text\" id=\"name\" th:field=\"*{name}\"\/>\n        <br\/>\n        <label for=\"email\">Email:<\/label>\n        <input type=\"text\" id=\"email\" th:field=\"*{email}\"\/>\n        <br\/>\n        <button type=\"submit\">Submit<\/button>\n    <\/form>\n<\/body>\n<\/html>\n<\/code><\/pre>\n\n\n\n
Step 2:<\/strong> Create a result template (result.html<\/code>).<\/p>\n\n\n\n
<!DOCTYPE html>\n<html xmlns:th=\"http:\/\/www.thymeleaf.org\">\n<head>\n    <title>Result Page<\/title>\n<\/head>\n<body>\n    <h1>Form Submitted Successfully!<\/h1>\n    <p>Name: <span th:text=\"${user.name}\"><\/span><\/p>\n    <p>Email: <span th:text=\"${user.email}\"><\/span><\/p>\n<\/body>\n<\/html>\n<\/code><\/pre>\n\n\n\n
Step 3:<\/strong> Create a User<\/code> class to hold form data.<\/p>\n\n\n\n
public class User {\r\n    private String name;\r\n    private String email;\r\n\r\n    \/\/ Getters and setters\r\n    public String getName() {\r\n        return name;\r\n    }\r\n\r\n    public void setName(String name) {\r\n        this.name = name;\r\n    }\r\n\r\n    public String getEmail() {\r\n        return email;\r\n    }\r\n\r\n    public void setEmail(String email) {\r\n        this.email = email;\r\n    }\r\n}\r<\/code><\/pre>\n\n\n\n
Step 4:<\/strong> Create a controller to handle form submissions.<\/p>\n\n\n\n
import org.springframework.stereotype.Controller;\r\nimport org.springframework.ui.Model;\r\nimport org.springframework.web.bind.annotation.GetMapping;\r\nimport org.springframework.web.bind.annotation.ModelAttribute;\r\nimport org.springframework.web.bind.annotation.PostMapping;\r\n\r\n@Controller\r\npublic class FormController {\r\n\r\n    @GetMapping(\"\/form\")\r\n    public String showForm(Model model) {\r\n        model.addAttribute(\"user\", new User());\r\n        return \"form\";\r\n    }\r\n\r\n    @PostMapping(\"\/submitForm\")\r\n    public String submitForm(@ModelAttribute User user, Model model) {\r\n        model.addAttribute(\"user\", user);\r\n        return \"result\";\r\n    }\r\n}\r<\/code><\/pre>\n\n\n\n
<\/p>\n\n\n\n
3. REST API with Spring Boot<\/h3>\n\n\n\n
Question:<\/strong> Write a simple REST API with Spring Boot.<\/p>\n\n\n\n
Answer:<\/strong> Step 1:<\/strong> Create a User<\/code> model class.<\/p>\n\n\n\n
public class User {\r\n    private Long id;\r\n    private String name;\r\n    private String email;\r\n\r\n    \/\/ Constructors, getters, and setters\r\n    public User() {}\r\n\r\n    public User(Long id, String name, String email) {\r\n        this.id = id;\r\n        this.name = name;\r\n        this.email = email;\r\n    }\r\n\r\n    public Long getId() {\r\n        return id;\r\n    }\r\n\r\n    public void setId(Long id) {\r\n        this.id = id;\r\n    }\r\n\r\n    public String getName() {\r\n        return name;\r\n    }\r\n\r\n    public void setName(String name) {\r\n        this.name = name;\r\n    }\r\n\r\n    public String getEmail() {\r\n        return email;\r\n    }\r\n\r\n    public void setEmail(String email) {\r\n        this.email = email;\r\n    }\r\n}\r<\/code><\/pre>\n\n\n\n
Step 2:<\/strong> Create a UserController<\/code> class to handle RESTful requests.<\/p>\n\n\n\n
import org.springframework.web.bind.annotation.GetMapping;\r\nimport org.springframework.web.bind.annotation.PathVariable;\r\nimport org.springframework.web.bind.annotation.PostMapping;\r\nimport org.springframework.web.bind.annotation.RequestBody;\r\nimport org.springframework.web.bind.annotation.RestController;\r\n\r\nimport java.util.ArrayList;\r\nimport java.util.List;\r\n\r\n@RestController\r\npublic class UserController {\r\n\r\n    private List<User> users = new ArrayList<>();\r\n\r\n    @GetMapping(\"\/users\")\r\n    public List<User> getUsers() {\r\n        return users;\r\n    }\r\n\r\n    @PostMapping(\"\/users\")\r\n    public User addUser(@RequestBody User user) {\r\n        user.setId((long) (users.size() + 1));\r\n        users.add(user);\r\n        return user;\r\n    }\r\n\r\n    @GetMapping(\"\/users\/{id}\")\r\n    public User getUserById(@PathVariable Long id) {\r\n        return users.stream()\r\n                    .filter(user -> user.getId().equals(id))\r\n                    .findFirst()\r\n                    .orElse(null);\r\n    }\r\n}\r<\/code><\/pre>\n\n\n\n
4. Exception Handling in Spring Boot<\/h3>\n\n\n\n
Question:<\/strong> Write a Spring Boot application demonstrating exception handling with @ControllerAdvice<\/code>.<\/p>\n\n\n\n
Answer:<\/strong> Step 1:<\/strong> Create a custom exception class.<\/p>\n\n\n\n
public class UserNotFoundException extends RuntimeException {\r\n    public UserNotFoundException(String message) {\r\n        super(message);\r\n    }\r\n}\r<\/code><\/pre>\n\n\n\n
Step 2:<\/strong> Modify the UserController<\/code> to throw the custom exception.<\/p>\n\n\n\n
import org.springframework.web.bind.annotation.*;\r\n\r\nimport java.util.ArrayList;\r\nimport java.util.List;\r\n\r\n@RestController\r\npublic class UserController {\r\n\r\n    private List<User> users = new ArrayList<>();\r\n\r\n    @GetMapping(\"\/users\")\r\n    public List<User> getUsers() {\r\n        return users;\r\n    }\r\n\r\n    @PostMapping(\"\/users\")\r\n    public User addUser(@RequestBody User user) {\r\n        user.setId((long) (users.size() + 1));\r\n        users.add(user);\r\n        return user;\r\n    }\r\n\r\n    @GetMapping(\"\/users\/{id}\")\r\n    public User getUserById(@PathVariable Long id) {\r\n        return users.stream()\r\n                    .filter(user -> user.getId().equals(id))\r\n                    .findFirst()\r\n                    .orElseThrow(() -> new UserNotFoundException(\"User not found with id: \" + id));\r\n    }\r\n}\r\n<\/code><\/pre>\n\n\n\n
Step 3:<\/strong> Create a GlobalExceptionHandler<\/code> class with @ControllerAdvice<\/code>.<\/p>\n\n\n\n
import org.springframework.http.HttpStatus;\r\nimport org.springframework.http.ResponseEntity;\r\nimport org.springframework.web.bind.annotation.ControllerAdvice;\r\nimport org.springframework.web.bind.annotation.ExceptionHandler;\r\nimport org.springframework.web.bind.annotation.ResponseStatus;\r\n\r\n@ControllerAdvice\r\npublic class GlobalExceptionHandler {\r\n\r\n    @ExceptionHandler(UserNotFoundException.class)\r\n    @ResponseStatus(HttpStatus.NOT_FOUND)\r\n    public ResponseEntity<String> handleUserNotFoundException(UserNotFoundException ex) {\r\n        return new ResponseEntity<>(ex.getMessage(), HttpStatus.NOT_FOUND);\r\n    }\r\n\r\n    \/\/ Other exception handlers can be added here\r\n}\r<\/code><\/pre>\n\n\n\n
<\/p>\n\n\n\n
5. Using Spring Data JPA<\/h3>\n\n\n\n
Question:<\/strong> Write a Spring Boot application using Spring Data JPA to perform CRUD operations.<\/p>\n\n\n\n
Answer:<\/strong> Step 1:<\/strong> Add the Spring Data JPA dependency in pom.xml<\/code>.<\/p>\n\n\n\n
<dependency>\r\n    <groupId>org.springframework.boot<\/groupId>\r\n    <artifactId>spring-boot-starter-data-jpa<\/artifactId>\r\n<\/dependency>\r\n<dependency>\r\n    <groupId>com.h2database<\/groupId>\r\n    <artifactId>h2<\/artifactId>\r\n    <scope>runtime<\/scope>\r\n<\/dependency>\r<\/code><\/pre>\n\n\n\n
Step 2:<\/strong> Create the User<\/code> entity class.<\/p>\n\n\n\n
import javax.persistence.Entity;\r\nimport javax.persistence.GeneratedValue;\r\nimport javax.persistence.GenerationType;\r\nimport javax.persistence.Id;\r\n\r\n@Entity\r\npublic class User {\r\n\r\n    @Id\r\n    @GeneratedValue(strategy = GenerationType.IDENTITY)\r\n    private Long id;\r\n    private String name;\r\n    private String email;\r\n\r\n    \/\/ Getters and setters\r\n    public Long getId() {\r\n        return id;\r\n    }\r\n\r\n    public void setId(Long id) {\r\n        this.id = id;\r\n    }\r\n\r\n    public String getName() {\r\n        return name;\r\n    }\r\n\r\n    public void setName(String name) {\r\n        this.name = name;\r\n    }\r\n\r\n    public String getEmail() {\r\n        return email;\r\n    }\r\n\r\n    public void setEmail(String email) {\r\n        this.email = email;\r\n    }\r\n}\r<\/code><\/pre>\n\n\n\n
Step 3:<\/strong> Create a UserRepository<\/code> interface<\/p>\n\n\n\n
import org.springframework.data.jpa.repository.JpaRepository;\r\n\r\npublic interface UserRepository extends JpaRepository<User, Long> {\r\n}\r<\/code><\/pre>\n\n\n\n
Step 4:<\/strong> Create a UserService<\/code> class<\/p>\n\n\n\n
import org.springframework.beans.factory.annotation.Autowired;\r\nimport org.springframework.stereotype.Service;\r\n\r\nimport java.util.List;\r\nimport java.util.Optional;\r\n\r\n@Service\r\npublic class UserService {\r\n\r\n    @Autowired\r\n    private UserRepository userRepository;\r\n\r\n    public List<User> getAllUsers() {\r\n        return userRepository.findAll();\r\n    }\r\n\r\n    public User getUserById(Long id) {\r\n        return userRepository.findById(id).orElse(null);\r\n    }\r\n\r\n    public User saveUser(User user) {\r\n        return userRepository.save(user);\r\n    }\r\n\r\n    public void deleteUser(Long id) {\r\n        userRepository.deleteById(id);\r\n    }\r\n}\r<\/code><\/pre>\n\n\n\n
Step 5:<\/strong> Create a UserController<\/code> class to handle HTTP requests.<\/p>\n\n\n\n
import org.springframework.beans.factory.annotation.Autowired;\r\nimport org.springframework.http.ResponseEntity;\r\nimport org.springframework.web.bind.annotation.*;\r\n\r\nimport java.util.List;\r\n\r\n@RestController\r\n@RequestMapping(\"\/users\")\r\npublic class UserController {\r\n\r\n    @Autowired\r\n    private UserService userService;\r\n\r\n    @GetMapping\r\n    public List<User> getAllUsers() {\r\n        return userService.getAllUsers();\r\n    }\r\n\r\n    @GetMapping(\"\/{id}\")\r\n    public ResponseEntity<User> getUserById(@PathVariable Long id) {\r\n        User user = userService.getUserById(id);\r\n        if (user == null) {\r\n            return ResponseEntity.notFound().build();\r\n        }\r\n        return ResponseEntity.ok(user);\r\n    }\r\n\r\n    @PostMapping\r\n    public User createUser(@RequestBody User user) {\r\n        return userService.saveUser(user);\r\n    }\r\n\r\n    @PutMapping(\"\/{id}\")\r\n    public ResponseEntity<User> updateUser(@PathVariable Long id, @RequestBody User user) {\r\n        User existingUser = userService.getUserById(id);\r\n        if (existingUser == null) {\r\n            return ResponseEntity.notFound().build();\r\n        }\r\n        user.setId(id);\r\n        return ResponseEntity.ok(userService.saveUser(user));\r\n    }\r\n\r\n    @DeleteMapping(\"\/{id}\")\r\n    public ResponseEntity<Void> deleteUser(@PathVariable Long id) {\r\n        User existingUser = userService.getUserById(id);\r\n        if (existingUser == null) {\r\n            return ResponseEntity.notFound().build();\r\n        }\r\n        userService.deleteUser(id);\r\n        return ResponseEntity.noContent().build();\r\n    }\r\n}\r<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
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