1. Button b1;
2. void setup(){
     size(200,200);
     b1=new Button(10,20,40,50);
   }
3. void draw(){
    b1.display();
   }
4. class AllButton{
   int x,y,l,b; 
5. AllButton(int xp,int yp, int la, int br){
       x=xp;
     y=yp;
     l=la;
     b=br;
    }
    
     void display(){
      rect(x,y,b,l);
     }
   }
6. class Button extends AllButton{
   Button(int xp, int yp, int la, int br){
     super(xp,yp,la, br);
   }
   void display(){
   super.display();
   }
   }
   
That's what I've tried with super... I don't understand what this "super" should help me. I've to write exaxtly as much as before.. I still must have a display-method in the Button-class and I still must have a Button constructor..

What's my fault?

thanks for your help.. :D

First question: visibly, you solved it yourself, you can have a constructor in the parent class.
Second question: the idea is that you can have a different constructor, but you still need to build the base class.
In general, the extending class is supposed to do more than the base class...
Let say you want it to add color but your buttons always has the same size:

1. class Button extends AllButton {
2.   color baseColor;
3.   Button(int xp, int yp, color c) {
4.     super(xp, yp, 50, 20);
5.     baseColor = c;
6.   }
7.   void display() {
8.     fill(baseColor);
9.     super.display();
10.   }
11. }

When a method just calls super.sameMethod(), you can just omit to (re)define it, Java will just take the one from the super class.