References

As you work with objects, it is important that you understand references. A reference is an address that indicates where an object's variables and methods are stored.

When we assign objects to variables or pass them to methods as parameters, we aren't actually passing the object itself or its copy – we are passing references to the objects themselves in memory.

To better understand how references work, let's illustrate this with an example.

Following is an example:

Create a new class called Rectangle, as follows:

public class Rectangle {

    int width;
    int height;

    public Rectangle(int width, int height){
        this.width = width;
        this.height = height;
    }

    public static void main(String[] args){
        Rectangle r1, r2;

        r1 = new Rectangle(100, 200);
        r2 = r1;

        r1.height = 300;
        r1.width = 400;
        System.out.println("r1: width= " + r1.width + ", height= " + r1.height);
        System.out.println("r2: width= " + r2.width...