Is Array Passing in Java by Value or by Reference?

Are Arrays Passed by Value or by Reference in Java?

Java differs from other programming languages in its approach to object handling. Unlike primitive types such as integers or characters, arrays in Java behave uniquely. To understand their behavior, it's crucial to distinguish between passing objects by value and by reference.

Passing by Value or Reference in Java

In Java, everything is passed by value. However, when passing an array, it's a bit more nuanced. Arrays are not primitives, but they are also not objects in the traditional sense. Instead, they are essentially references to an object on the heap.

When an array is passed to a method, the reference to the array is passed by value. This means that a copy of the reference is passed, not the actual array itself.

Implications for Array Behavior

Since the reference to the array is passed by value, any changes made to the content of the array through that reference will affect the original array. For example, if an array element's value is modified within a method, the change will be reflected in the original array.

However, changing the reference itself to point to a different array will not change the original reference in the method. In other words, the reference that was passed to the method remains the same, even if the array it points to is changed.

Code Example for Clarity

To illustrate this concept, consider the following code:

public static void changeContent(int[] arr) {
    // If we change the content of arr.
    arr[0] = 10;  // Will change the content of array in main()
}

public static void changeRef(int[] arr) {
    // If we change the reference
    arr = new int[2];  // Will not change the array in main()
    arr[0] = 15;
}

public static void main(String[] args) {
    int[] arr = new int[2];
    arr[0] = 4;
    arr[1] = 5;

    changeContent(arr);

    System.out.println(arr[0]);  // Will print 10.. 

    changeRef(arr);

    System.out.println(arr[0]);  // Will still print 10.. 
                                 // Change the reference doesn't reflect change here..
}

In this example, the changeContent method modifies the content of the array by setting the first element to 10. The changes are reflected in the original array in main. This demonstrates that modifying the content of an array passed by reference affects the original array.

On the other hand, the changeRef method assigns a new array to the reference arr. This change is not reflected in the original array in main because the reference itself is not passed by value.

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