How to open multiple windows with Processing?

I’m trying to create two windows with Processing. Before you mark this as a duplicate, as there are other questions similar to this, I have a specific error and I can’t find a solution. When I try to add(s) I get the error The method add(Component) in the type Container is not applicable for the arguments (evolution_simulator.SecondApplet)

I’m not sure how to fix this, and any help would be appreciated. Here is the code:

import javax.swing.*;

PFrame f;

void setup() {
    size(320, 240);
    f = new PFrame();
}

void draw() {

}

public class PFrame extends JFrame {

    SecondApplet s;

    public PFrame() {
        setBounds(100,100,400,300);
        s = new SecondApplet();
        add(s);  // error occurs here
        s.init();
        show();
    }
}

public class SecondApplet extends PApplet {

    public void setup() {
        size(400, 300);
        noLoop();
    }

    public void draw() {

    }
}

Answer

The reason for the error message is because the add() function is expecting a Component, and PApplet is not a Component. This is because PApplet no longer extends Applet as of Processing 3, so old code that uses it as a Component will no longer work.

Instead, you can create a class that extends PApplet for your second window, and then call PApplet.runSketch() using that second PApplet as a parameter:

void setup() {
  size(100, 100);

  String[] args = {"TwoFrameTest"};
  SecondApplet sa = new SecondApplet();
  PApplet.runSketch(args, sa);
}

void draw() {
  background(0);
  ellipse(50, 50, 10, 10);
}     

public class SecondApplet extends PApplet {

  public void settings() {
    size(200, 100);
  }
  public void draw() {
    background(255);
    fill(0);
    ellipse(100, 50, 10, 10);
  }
}