从另一个 JFrame 调用方法

Question

I want to get a JFrame (createFrame) from another JFrame (mainFrame). I created a method in the mainFrame which returns the createFrame, so that I can dispose the createFrame when clicking a button in the createFrame. But I cant call this methode (getCreateFrame) from the second JFrame (createFrame).

MainFrame.java

import frames.SelectFrame;

import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class MainFrame extends JFrame{
    private JPanel mainPanel;
    private JComboBox cbOption;
    private JButton btConfirm;
    private JLabel lbCredit;
    private JFrame createFrame;

    public static void main(String[] args) {
        JFrame mainFrame = new JFrame("");
        mainFrame.setContentPane(new MainFrame().mainPanel);
        mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        mainFrame.pack();
        mainFrame.setVisible(true);
        mainFrame.setBounds(500, 500, 400, 400);
    }

    public MainFrame() {
        btConfirm.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                int option = cbOption.getSelectedIndex();
                System.out.println(option);
                if(option == 0){
                    JFrame createFrame = new SelectFrame();
                    createFrame.setContentPane(new SelectFrame().mainPanel);
                    createFrame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
                    createFrame.pack();
                    createFrame.setVisible(true);
                    createFrame.setBounds(500, 500, 400, 400);
                    System.out.println("Frame created!");
                } else if(option == 1){

                }  else{

                }
            }
        });
    }
    public final JFrame getCreateFrame(){
        return createFrame;
    }
}

CreateFrame.java

package frames;

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.sql.Date;

public class SelectFrame extends JFrame{
    public JPanel mainPanel;
    private JLabel lbCredit;
    private JComboBox cbxCurrency;
    private JButton btConfirm;
    private JButton btExit;

    public SelectFrame() {
        btConfirm.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {

            }
        });

        btExit.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {

            }
        });
    }
}

Answer 1

To answer your question I believe you should take a look at Programming scope .

If you want to access the getCreateFrame() method in your SelectFrame -class you will need to be able to reach the MainFrame -class somehow since this holds the method.

createFrame is a private variable of the MainFrame -class which means it's only accessible within the class. Which is why (as you have done) you need a get-method to retrieve it. Although, when you call the get-method you want to know which object's createFrame you are trying to access. The question is, how will SelectFrame know which method to call?

If you edit your SelectFrame -class alike this:

public class SelectFrame extends JFrame {

    private MainFrame mFrame;

    public SelectFrame(MainFrame frame) {
        mFrame = frame;
    }

}

You can now call the getCreateFrame() from the MainFrame you pass to SelectFrame 's constructor within the SelectFrame class. ( mFrame.getCreateFrame(); )

Note: In the MainFrame -class's constructor you initialize your createFrame in an if -statement which means it will give you null unless option == 0 .

if(option == 0) {
    JFrame createFrame = new SelectFrame(); 
}

Answer 2

Your returned createFrame is null. This is due to the fact that you have introduced an local instance of JFrame createFrame = new SelectFrame(); in the MainFram constructor

public final JFrame getCreateFrame(){
     return createFrame;
}

Answer 3

In your constructor, you are creating a local variable instead of assigning to the instance variable you created.

JFrame createFrame = new SelectFrame();

Should instead have been:

createFrame = new SelectFrame();

Don't create a new variable, assign to the existin one.