public class rectangle {
private int w;
private int h;
public rectangle(int wi, int he) { w=wi; h=he;}
public int getWidth() {return w;}
public int getHeight() {return h;}
public void setWidth(int wi) { w= wi;}
public void setHeight(int he) {h=he;}
}

public class carré extends rectangle {
public carré(int cote) { super(cote,cote); }
public void setcote(int cote) {setWidth(cote); setHeight(cote); }
}

et hop fini