50+ Interview Questions on Java Programming Language

Where to get the latest interview questions on Java?

You might struggle with such questions if you want to hire the best talent in the market for Java in your organisation. 

Worry not, as we are here to help every interviewer with the latest interview questions on Java programming language. These questions will help you analyse the shortlisted applicants precisely and filter the best one for your company.

Technology is leaping every day, and ideally, you must have an expert in every technology in your company. If you do not have one for Java, try HyreSnap Interview as a Service Platform. 

This platform has subject matter experts of 450+ technologies who can help you execute the entire interview and get the best Java person for your business.

If you have a Java expert in your team, below are some steps and questions that will help you execute a fruitful Java interview for your company:

As an interviewer, preparing yourself before conducting an interview is important. Here are some things you should arrange before the interview:

Review the candidate's resume and application materials: Before the interview, carefully review the candidate's resume and application materials to familiarise yourself with their skills, experience, and qualifications.

Develop a list of questions: Develop a list of relevant questions that will help you determine the candidate's qualifications, experience, and fit for the position.

Schedule the interview: Contact the candidate to schedule the interview and ensure that both parties agree on the date and time.

Familiarise yourself with the job description: Make sure you understand the job description and the qualifications needed for the position.

Determine the evaluation criteria: Determine the criteria you will use to evaluate the candidate, such as technical skills, communication skills, and fit with the company culture.

Arrange for multiple interviewers: Consider having multiple interviewers to ensure you get a well-rounded candidate evaluation.

Prepare a scoring system: Develop a scoring system to evaluate the candidate's responses to the questions and their overall fit for the position.

Set expectations with the candidate: Let the candidate know what to expect during the interview, such as the format and the types of questions that will be asked. This will help the candidate feel more comfortable and prepared.

What is Java programming language?

Java is a high-level, object-oriented programming language developed by Sun Microsystems and now owned by Oracle Corporation. It is used to develop applications on various platforms, including Windows, Linux, and Mac OS.

What is the difference between JDK, JRE, and JVM?

JDK stands for Java Development Kit, which contains the tools necessary for developing Java applications, including the Java compiler, JavaDoc, and other tools.

JRE stands for Java Runtime Environment, which provides the environment in which Java applications can run but does not include development tools.

JVM stands for Java Virtual Machine, which runs Java bytecode.

What are the features of Java?

Some of the key features of Java include platform independence, object-oriented programming, automatic memory management, security, and scalability.

What is the difference between a class and an object?

A class is a blueprint for creating objects, while an object is an instance of a class.

What is a constructor?

A constructor is a special method that is used to create objects of a class. It is called automatically when an object is created.

What is the difference between a constructor and a method?

A constructor is a special method used to create objects, while a method is a regular function that performs some action.

What is an interface in Java?

An interface in Java is a collection of abstract methods and constants. It is used to define a contract for classes that implement the interface.

What is inheritance in Java?

Inheritance is a mechanism in Java that allows a class to inherit properties and methods from another class.

What is polymorphism in Java?

Polymorphism is a mechanism in Java that allows objects of different classes to be treated as objects of the same class.

What is encapsulation in Java?

Encapsulation is a mechanism in Java that allows the hiding of implementation details of a class from other classes.

What is an abstraction in Java?

Abstraction is a mechanism in Java that allows the creation of abstract classes and interfaces to provide a high-level view of related classes.

What is a package in Java?

A package in Java is a collection of related classes and interfaces.

What is a thread in Java?

A thread in Java is a lightweight process that runs concurrently with other threads within the same program.

What is synchronisation in Java?

Synchronisation is a Java mechanism that controls access to shared resources in a multi-threaded environment.

What is the difference between final, finally, and finalise in Java?

final is a keyword in Java that is used to declare a constant.

finally is a block in Java used to execute code regardless of whether an exception is thrown or not.

finalise is a method in Java that the garbage collector calls before an object is destroyed.

What is a static variable in Java?

A static variable in Java is a variable that is associated with the class rather than with an instance of the class.

What is a static method in Java?

A static method in Java is a method that is associated with the class rather than with an instance of the class.

What is a final variable in Java?

A final variable in Java is a variable that can only be assigned once and cannot be changed afterward.

What is a final class in Java?

A final class in Java is a class that cannot be extended by other classes.

What is a try-catch block in Java?

A try-catch block in Java is used to handle exceptions that may occur during the execution of a program.

What is a constructor chaining in Java?

Constructor chaining is a mechanism in Java that allows a constructor to call another constructor in the same class or the parent class using the 'this' and 'super' keywords.

What is the purpose of the 'static' keyword in Java?

The 'static' keyword in Java is used to define a variable or method that belongs to the class rather than an instance of the class.

What is an abstract class in Java?

An abstract class in Java is a class that cannot be instantiated and is intended to be subclassed by other classes.

What is the difference between abstract class and interface in Java?

An interface in Java is a collection of abstract methods and constants, while an abstract class is a class that cannot be instantiated and is intended to be subclassed by other classes.

What is a generic class in Java?

A generic class in Java is a class that can work with different types of objects by using type parameters.

What is the difference between a HashMap and a HashTable in Java?

A HashMap in Java is a class that stores key-value pairs in a hash table, while a HashTable is a synchronized implementation of a hash table.

What is the difference between a List and a Set in Java?

A List in Java is an ordered collection of elements that allows duplicates, while a Set is a collection of unique elements with no defined order.

What is the difference between an ArrayList and a LinkedList in Java?

An ArrayList in Java is an implementation of the List interface that stores elements in an array, while a LinkedList is an implementation of the List interface that stores elements in a doubly-linked list.

What is the difference between an interface and an abstract class in Java?

An interface in Java is a collection of abstract methods and constants, while an abstract class is a class that cannot be instantiated and is intended to be subclassed by other classes.

What is the difference between a private and a protected variable in Java?

A private variable in Java can only be accessed within the same class, while a protected variable can be accessed within the same class or subclasses.

What is the difference between a class variable and an instance variable in Java?

A class variable in Java is a variable that belongs to the class, while an instance variable is a variable that belongs to an instance of the class.

What is the difference between method overloading and method overriding in Java?

Method overloading in Java is when two or more methods in the same class have the same name but different parameters, while method overriding is when a subclass provides a specific implementation of a method already defined in the parent class.

What is the purpose of the 'this' keyword in Java?

The 'this' keyword in Java is used to refer to the current object.

What is the purpose of the 'super' keyword in Java?

The 'super' keyword in Java is used to refer to the parent class.

What is the difference between a StringBuilder and a StringBuffer in Java?

A StringBuilder in Java is a class that provides a mutable sequence of characters, while a StringBuffer is a thread-safe implementation of a mutable sequence of characters.

What is the difference between a public and a protected class in Java?

A public class in Java can be accessed from any other class, while a protected class can only be accessed within the same package or subclasses.

What is the difference between a checked and an unchecked exception in Java?

A checked exception in Java is a type of exception that must be handled by the calling method or propagated up the call stack, while an unchecked exception is a type of exception that does not need to be explicitly handled.

How does Java handle garbage collection?

Java uses a garbage collector to manage memory allocation and deallocation for objects automatically. The garbage collector identifies no longer used objects and frees up memory for reuse.

How does Java implement multithreading?

Java uses the Thread class and the Runnable interface to implement multithreading. Each thread is executed independently, allowing for concurrent execution of multiple tasks.

What is the difference between a Thread and a Process in Java?

A Thread in Java is a lightweight unit of execution within a process, while a Process is a separate instance of a program that runs in its own memory space.

What is the difference between an InputStream and an OutputStream in Java?

An InputStream in Java is a class used for reading data from a source, while an OutputStream is used for writing data to a destination.

What is the difference between a Reader and a Writer in Java?

A Reader in Java is a class used for reading character data from a source, while a Writer is a class used for writing character data to a destination.

What is the difference between a synchronised block and a synchronised method in Java?

A synchronised block in Java allows for synchronisation of specific code blocks within a method, while a synchronised method synchronises the entire method.

What is the difference between the Stack and Queue data structures in Java?

A Stack in Java is a Last In First Out (LIFO) data structure, while a Queue is a First In First Out (FIFO) data structure.

What is the difference between a TreeSet and a TreeMap in Java?

A TreeSet in Java is an implementation of the Set interface that stores elements in sorted order, while a TreeMap is an implementation of the Map interface that stores key-value pairs in sorted order.

What is the difference between a FileInputStream and a FileReader in Java?

A FileInputStream in Java is a class used for reading binary data from a file, while a FileReader is a class used for reading character data from a file.

What is the difference between a FileOutputStream and a FileWriter in Java?

A FileOutputStream in Java is a class used for writing binary data to a file, while a FileWriter is a class used for writing character data to a file.

What is the difference between an anonymous inner class and a lambda expression in Java?

An anonymous inner class in Java is a class defined without a name used to implement a single abstract method or interface. At the same time, a lambda expression is a shorter syntax for defining a functional interface.

What is the difference between a shallow copy and a deep copy in Java?

A shallow copy in Java creates a new object that shares the same references to the original object's data, while a deep copy creates a new object with its own copy of the original object's data.

What is the difference between static and non-static methods in Java?

A static method in Java belongs to the class and can be called without creating an instance of the class, while a non-static method belongs to an instance of the class and can only be called on that instance.

Write a program to find the largest and smallest number in an array of integers.

public class Main {

   public static void main(String[] args) {

      int[] numbers = {10, 2, 33, 44, 8, 6, 19};

      int smallest = numbers[0];

      int largest = numbers[0];

      for(int i = 1; i < numbers.length; i++) {

         if(numbers[i] > largest) {

            largest = numbers[i];

         }

         else if(numbers[i] < smallest) {

            smallest = numbers[i];

         }

      }

      System.out.println("Smallest number: " + smallest);

      System.out.println("Largest number: " + largest);

   }

}

Write a program to implement a stack using an array in Java.

public class Stack {

   private int[] arr;

   private int top;

   private int capacity;

   public Stack(int capacity) {

      this.capacity = capacity;

      this.arr = new int[capacity];

      this.top = -1;

   }

   public void push(int value) {

      if(isFull()) {

         throw new RuntimeException("Stack is full");

      }

      arr[++top] = value;

   }

   public int pop() {

      if(isEmpty()) {

         throw new RuntimeException("Stack is empty");

      }

      return arr[top--];

   }

   public boolean isEmpty() {

      return top == -1;

   }

   public boolean isFull() {

      return top == capacity - 1;

   }

}

Write a program to implement a binary search algorithm in Java.

public class BinarySearch {

   public static void main(String[] args) {

      int[] numbers = {2, 6, 8, 11, 15, 20, 25};

      int searchValue = 15;

      int result = binarySearch(numbers, searchValue);

      if(result == -1) {

         System.out.println("Value not found in array");

      }

      else {

         System.out.println("Value found at index: " + result);

      }

   }

   public static int binarySearch(int[] arr, int searchValue) {

      int low = 0;

      int high = arr.length - 1;

      while(low <= high) {

         int mid = (low + high) / 2;

         if(arr[mid] == searchValue) {

            return mid;

         }

         else if(arr[mid] < searchValue) {

            low = mid + 1;

         }

         else {

            high = mid - 1;

         }

      }

      return -1;

   }

}

Write a program to implement a binary tree in Java.

public class Node {

   int value;

   Node left;

   Node right;

   public Node(int value) {

      this.value = value;

      this.left = null;

      this.right = null;

   }

}

public class BinaryTree {

   Node root;

   public BinaryTree() {

      this.root = null;

   }

   public void insert(int value) {

      root = insertRecursive(root, value);

   }

   private Node insertRecursive(Node current, int value) {

      if(current == null) {

         return new Node(value);

      }

      if(value < current.value) {

         current.left = insertRecursive(current.left, value);

      }

      else if(value > current.value) {

         current.right = insertRecursive(current.right, value);

      }

      return current;

   }

Write a program to implement a merge sort algorithm in Java.

public class MergeSort {

   public static void main(String[] args) {

      int[] numbers = {3, 5, 1, 8, 2, 9, 4};

      mergeSort(numbers, 0, numbers.length - 1);

      for(int i = 0; i < numbers.length; i++) {

         System.out.print(numbers[i] + " ");

      }

   }

   public static void mergeSort(int[] arr, int low, int high) {

      if(low < high) {

         int middle = (low + high) / 2;

         mergeSort(arr, low, middle);

         mergeSort(arr, middle + 1, high);

         merge(arr, low, middle, high);

      }

   }

   public static void merge(int[] arr, int low, int middle, int high) {

      int[] temp = new int[arr.length];

      for(int i = low; i <= high; i++) {

         temp[i] = arr[i];

      }

      int i = low;

      int j = middle + 1;

      int k = low;

      while(i <= middle && j <= high) {

         if(temp[i] <= temp[j]) {

            arr[k] = temp[i];

            i++;

         }

         else {

            arr[k] = temp[j];

            j++;

         }

         k++;

      }

      while(i <= middle) {

         arr[k] = temp[i];

         k++;

         i++;

      }

   }

}

Write a program to find all possible permutations of a string in Java.

public class Permutations {

   public static void main(String[] args) {

      String input = "abc";

      printPermutations(input, "");

   }

   public static void printPermutations(String input, String output) {

      if(input.length() == 0) {

         System.out.println(output);

         return;

      }

      for(int i = 0; i < input.length(); i++) {

         char ch = input.charAt(i);

         String leftSubstring = input.substring(0, i);

         String rightSubstring = input.substring(i + 1);

         String newInput = leftSubstring + rightSubstring;

         printPermutations(newInput, output + ch);

      }

   }

}

Write a program to find the longest palindrome substring in a given string in Java.

public class LongestPalindrome {

   public static void main(String[] args) {

      String input = "babad";

      String result = findLongestPalindrome(input);

      System.out.println("Longest palindrome: " + result);

   }

   public static String findLongestPalindrome(String input) {

      String longestPalindrome = "";

      for(int i = 0; i < input.length(); i++) {

         for(int j = i + 1; j <= input.length(); j++) {

            String substring = input.substring(i, j);

            if(isPalindrome(substring) && substring.length() > longestPalindrome.length()) {

               longestPalindrome = substring;

            }

         }

      }

      return longestPalindrome;

   }

   public static boolean isPalindrome(String input) {

      int length = input.length();

      for(int i = 0; i < length / 2; i++) {

         if(input.charAt(i) != input.charAt(length - i - 1)) {

            return false;

         }

      }

      return true;

   }

}

Executing an interview and hiring a suitable talent for your organisation is one of your business's most important growth aspects. A wrong hire can affect your company's growth in the long run.

Hence, we recommend using HyreSnap Interview as a Service platform to hire the best Java applicant in your company. Below are the features of our AI-powered Interview as a Service platform:

Features of HyreSnap Interview as a Service platform:

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Key Takeaways

Interview execution and report generation is complex even for expert recruiters. Hence, if you do not want to engage your company assets in the hiring process, use HyreSnap Interview as a Service platform.

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