JButton accessible for several Panels - class

Question

I'm new at Java Programming and have "beginner Question".
I already tried to find wether someone already had the same problem, but I couldn't find any posts which were on my low level.
My Problem:
I have 2 JPanels in one of them, (let's call it Panel1) I implements a JTextField (field1) and a JButton (button1). on Panel2 I want to draw something, depending on what the using tipped in the first JTextField.
My Problem is I want Panel2 to "see" that button1 (in Panel1) , which I don't manage to do.
Can anyone give me a hint, a Youtube Video or something like that, where I can see a nice example where someone handles such a Problem?
Greetings Ventura
P.S I had an idea to pass values to Panel2 where it should draw those things I want, here my code up so far (I hope I post it correctly): Here Panel1:
public class Panel1 extends JPanel
{
public JButton button = new JButton("OK");
public JTextField field1 = new JTextField(5);
public String name;int b;
public Panel1()
{
setBackground(Color.WHITE);
add(field1);
add(button);
ButtonListener listener = new ButtonListener(field1);
button.addActionListener(listener);
}
public Dimension getPreferredSize()
{
return new Dimension(400,400);
}
}
Here the ButtonListener :
class ButtonListener implements ActionListener
{
Graphics g;
//Graphics2D g2 = (Graphics2D) g;
public Panel2 pan2 = new Panel2();
public String name;
public JTextField field1 = new JTextField();
int b;
public ButtonListener(JTextField field1)
{this.field1 = field1;}
public void actionPerformed(ActionEvent e)
{
String op = e.getActionCommand();
if(op.equals("OK"))
{
name = field1.getText();
try
{
b = Integer.parseInt(name);
JOptionPane.showMessageDialog(null,"Ihre Zahl = "+b);
pan2.setvalue(b,g);
}
catch(NumberFormatException ex) {JOptionPane.showMessageDialog(null,"Please enter real numbers!");}
}
}
}
And finally Panel2 where I'd like to draw things based on the Input given in Panel1 (for example: I type in 10 and he draws me a Rectangle with width 10 or something like that)
public class Panel2 extends JPanel
{
Graphics g;
Graphics2D g2 = (Graphics2D) g;
public int b;
public Panel2()
{
setBackground(Color.YELLOW);
}
public void paintComponent(Graphics g)
{
Graphics2D g2 = (Graphics2D) g;
super.paintComponent(g);
g2.setColor(Color.RED);
g2.fillRect(200, 200, 50, 50);
Paint2(g);
}
public void Paint2(Graphics g)
{
this.g = g;
Graphics2D g2 = (Graphics2D) g;
//super.paintComponent(g);
System.out.println("TEST2");
g2.setColor(Color.BLUE);
//System.out.println("TEST3");
g2.fillRect(10 , 10, 40, 40);
}
public void setvalue(int b, Graphics g)
{
this.b = b;
this.g = g;
Graphics2D g2 = (Graphics2D) g;
g2.setColor(Color.CYAN);
g2.fillRect(0, 0, 40, 40);
System.out.println("B ist gleich = "+b);
//Paint2(g2);
}
public Dimension getPreferredSize()
{
return new Dimension(400,400);
}
I'm sorry if it is a little cumbersome to read.
My basic Problem I get in this code is the NullpointerException in Panel2 when I want to call the Method
setvalue(int b, Graphics g)
g2.setColor(Color.Cyan)
Greetings Patrick

Answer 1

I did a redesign to most of Panel1 and a little bit to Panel2.
I'm going to start with Panel2 because it's simpler. Here is the new code:
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JPanel;
public class Panel2 extends JPanel {
Graphics g;
Graphics2D g2;
public int b;
public Panel2() {
setBackground(Color.YELLOW);
b = 50;
}
#Override
public void paintComponent(Graphics g) {
g2 = (Graphics2D) g;
super.paintComponent(g);
g2.setColor(Color.RED);
g2.fillRect(200, 200, 50, 50);
g2.setColor(Color.BLUE);
g2.fillRect(10, 10, 40, 40);
g2.setColor(Color.CYAN);
g2.fillRect(b, b, 40, 40);
}
public void setValue(int b) {
this.b = b;
System.out.println("B ist gleich = " + b);
repaint();
}
#Override
public Dimension getPreferredSize() {
return new Dimension(400, 400);
}
}
The biggest change that I made to Panel2 is that I made g2 a class variable that all the methods can use. Instead of making the methods take a Graphics variable each time, I just made it so that they can use the one from the class. I also didn't make a new Graphics2D variable "equal" anything each time the method was called because there was no need for that. The only place I updated it in was the paintComponent() method so that I could update it once for the whole class.
Next up is Panel1. Here is the code:
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;
public class Panel1 extends JPanel {
public JButton button = new JButton("OK");
public JTextField field1 = new JTextField(5);
public String name;
int b;
private Panel2 pan2;
public Panel1() {
setBackground(Color.WHITE);
add(field1);
add(button);
ActionListener listener = new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
String op = e.getActionCommand();
if (op.equals("OK")) {
name = field1.getText();
try {
b = Integer.parseInt(name);
pan2.setValue(b);
JOptionPane.showMessageDialog(null, "Ihre Zahl = " + b);
} catch (NumberFormatException ex) {
JOptionPane.showMessageDialog(null, "Please enter real numbers!");
}
}
}
};
button.addActionListener(listener);
}
public void setSecondPanel(Panel2 panel) {
pan2 = panel;
}
#Override
public Dimension getPreferredSize() {
return new Dimension(400, 400);
}
public static void main(String[] args) {
JFrame frame = new JFrame();
Panel1 pan1 = new Panel1();
Panel2 pan2 = new Panel2();
pan1.setSecondPanel(pan2);
frame.setSize(pan1.getPreferredSize().width + pan2.getPreferredSize().width, pan1.getPreferredSize().height);
frame.add(pan2, BorderLayout.EAST);
frame.add(pan1, BorderLayout.WEST);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
First of all, notice how I didn't create a ButtonListener. Because you're only using it once, there's no need to create a new class for it (it's also less code).
In the main() method, I made it so that it adds both panels to the opposite sides so that they won't overlap each other or anything.
Finally, I created a setSecondPanel method in the Panel1 class so that the class would have a Panel2 variable to work with at any time.