Why I am able to pass a bigger array into a smaller array in Java?

Question

This might be a silly question but does a Java array accept more than its size? If yes then why do we need ArrayList? I thought that arrays had a fixed size that can't be increased at runtime. Here is my test code:

public class ArraySizeDemo {
    int[] anArray = new int[5];

    public int[] getAnArray() {
        return anArray;
    }

    public void setAnArray(int[] anArray) {
        this.anArray = anArray;
    }
}

public class ArrayDemo {
    public static void main(String[] args) {
        ArraySizeDemo ar = new ArraySizeDemo();

        int arr[] = {0,1,2,3,4,5,6,7,8,9};
        int testarray[] = new int[10];
        ar.setAnArray(arr); // it should give an error here since I am trying to 
        // assign an array of 10 to an array of 5
        testarray = ar.getAnArray();
        for (int i = 0; i < arr.length; i++)
            System.out.println(testarray[i]);
    }
}

Answer 1

The assignment

this.anArray = anArray;

doesn't copy the elements of anArray to this.anArray.

It changes the value of the this.anArray variable to refer to the same array referenced by anArray. Therefore, before the assignment this.anArray refers to an array of length 5, and after the assignment it refers to a different array object of length 10.

If instead of this assignment you attempted to copy elements of the source array to the (smaller) target array, an exception would have been thrown, since the length of an array cannot be changed, so the elements of an array of length 10 cannot fit in an array of length 5.

Answer 2

You are changing the reference of this.anArray doing this.anArray = anArray;.

After that assignment, this.anArray is a reference pointing to another array, the one of ten elements.