Java Array Interview Questions and Answers 2025: Must-Know FAQs for Developers

1. What is an Array in Java?                                                                           Imp question for fresher

An Array in Java is a collection of elements that are of the same type. Arrays are fixed in size, meaning you cannot change their size once created. Arrays are stored in heap memory, not in stack memory. If you try to access an invalid index of an array, it will result in an exception.

Important Note: Array indices in Java always start from 0.

Types of Arrays in Java:

1. Single Dimensional Array:

   int a[] = new int[5];  // Declaration and instantiation
   int a[] = {33, 3, 4, 5};  // Declaration, instantiation, and initialization
   

2. Multidimensional Array:

   int[][] arr = new int[3][3];  // 3 rows and 3 columns
   

2. What is the Default Value of Array for Different Data Types?

3. Can You Change the Size of an Array in Java After Creation?                       Imp question for fresher

No, you cannot change the size of an array once it has been created. However, there are other data structures like ArrayList that allow resizing after creation.

4. Can You Pass a Negative Number in Array Size?                              Imp question for fresher

No, you cannot pass a negative number as the array size. If you do, you will not get a compiler error. Instead, you will get a NegativeArraySizeException at runtime.

5. Can You Declare an Array Without Array Size?                               Imp question for fresher

No, you cannot declare an array without specifying its size. If you try to do this, you will get a compile-time error.

6. Where is an Array Stored in JVM Memory?

In Java, an array is an object. So, arrays are stored in heap memory in the JVM.

7. Given a Primitive Array in Java, Where is it Stored in JVM?

Even if the array holds primitive elements, it is always considered an object and stored in heap memory.

8. What is ArrayStoreException? When is This Exception Thrown?     

                                                                                                              Imp question for fresher & experience

ArrayStoreException is a runtime exception. It occurs when you try to store an incompatible object type in an array. For example, if you try to store an Integer in a String array, you will get this exception.

Example:

public class ArrayDemo {
    public static void main(String args[]) {
        Object x[] = new String[3];
        x[0] = new Integer(0);  // Throws ArrayStoreException
    }
}

9. What is the Difference Between ArrayStoreException and ArrayIndexOutOfBoundsException?                                                                                                               Imp question for fresher & experience                                         

• ArrayStoreException is thrown when you try to store an incompatible object in an array. For example, trying to store an Integer in a String array.
• ArrayIndexOutOfBoundsException is thrown when you try to access an array with an invalid index. This could be an index that is negative or greater than or equal to the array size.

10. What Are the Advantages of Arrays?                                      Imp question for fresher & experience

• Efficient Access: You can access any element of an array in constant time using the index (O(1)).
• Sorting: Arrays allow you to sort multiple elements easily at once.

11. What Are the Disadvantages of Arrays?                                Imp question for fresher & experience

• Memory Requirement: Arrays require contiguous memory. In some cases, even if enough memory is available, it might not be contiguous.
• Fixed Size: Once created, the size of the array cannot be changed. You cannot increase or decrease the size after creation.

12. Write a Program to Print Elements of an Array

public class ArrayDemo {
    public static void main(String args[]) {
        int[] rollNumber = {23, 17, 20, 29, 30};
        
        for (int temp : rollNumber) {
            System.out.print(temp + " ");
        }
    }
}

Note : Array Notes (Mostly Asked in Interviews)                         Imp question for fresher & experience

Arrays are an essential concept in Java, often covered in interviews. Understanding their properties and limitations is crucial for Java developers. Always remember the following:

1. Arrays are fixed in size.
2. They must hold elements of the same data type.
3. The size must be non-negative.
4. Arrays are stored in heap memory in JVM.

public class ArrayDemo {
    public static void main(String args[]) {
        int[] original = {10, 20, 30};
        int[] cloned = original.clone();  // Cloning the array
        
        for (int i : cloned) {
            System.out.print(i + " ");  // Output: 10 20 30
        }
    }
}

public class ArrayDemo {
    public static void main(String args[]) {
        int[] a = {1, 2, 3};
        int[] b = a;  // Both 'a' and 'b' reference the same array
        
        System.out.println(b[0]);  // Output: 1
    }
}

public class ArrayDemo {
    public static void main(String args[]) {
        int[] a = {1, 2, 3, 4, 5};
        System.out.println(a.length);  // Output: 5
    }
}

import java.util.Arrays;

public class ArrayDemo {
    public static void main(String args[]) {
        int[] a = {5, 2, 8, 1, 3};
        Arrays.sort(a);  // Sorting the array
        
        for (int i : a) {
            System.out.print(i + " ");  // Output: 1 2 3 5 8
        }
    }
}

public class ArrayDemo {
    public static void main(String args[]) {
        int[] a = {1, 2, 3, 4, 5};
        
        int start = 0;
        int end = a.length - 1;
        
        while (start < end) {
            int temp = a[start];
            a[start] = a[end];
            a[end] = temp;
            start++;
            end--;
        }
        
        for (int i : a) {
            System.out.print(i + " ");  // Output: 5 4 3 2 1
        }
    }
}

By mastering these key concepts, you’ll be well-prepared for Java array-related interview questions!