INSTÂNCIA EM JAVA

class Retangulo{
    public int width, height;

    public int areaTotal(){
        return width * height;
    }
    public boolean isQuadrado(){
        if(width==height)
            return true;
        return false;
    }
}

public class Main {

    public static void main(String args[]){
        Retangulo r1 = new Retangulo();
        Retangulo r2;

        r2 = r1;
        r1.width = 1000;

        int i1 = 10;
        int i2 = i1;
        i2 = 20;

        //System.out.println(r1.width);
        //System.out.println(r2.width);

        System.out.println(i1);
        System.out.println(i2);
    }

}