使用和显示来自differentnet类的JLabel

Question

I am a beginner java programmer. I have two classes both in package1. I am trying to use a JLabel from another class in Main , here are the two pieces of code:

package package1;
import package1.*;

import javax.swing.*;

import java.awt.event.*;

public class Main extends JPanel implements ActionListener {
//Event Text
    protected static JLabel eventText;
    public void event1() {
    eventText = event1.event1EventText;
   }
   private static void createAndShowGUI() {
        JFrame frame = new JFrame("Stack Overflow");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Main newContentPane = new Main();
        newContentPane.setOpaque(true);
        frame.setContentPane(newContentPane);
        frame.setSize(1300, 700);
        frame.setVisible(true);
    }
    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();  
            }
        });
    }
}

My second file just makes a JLabel.

package package1;

import javax.swing.*;

public class event1 extends JPanel {
    protected static JLabel event1EventText;
    public static void main(String[] args) {
        event1EventText = new JLabel();
        event1EventText.setText("Some text");
    }
}

I need to use event1EventText in Main . I do not get any error when I run the code but eventText never displays. I just get a empty window.

Answer 1

哦，我认为问题是您没有将main类中的eventText放在方法createAndShowGUI中的框架中。

Answer 2

Try this solution :-

package package1;

import javax.swing.*;

import java.awt.event.*;

public class Main extends JPanel implements ActionListener {
//Event Text
    protected static JLabel eventText;
    public static void event1() {
    eventText = event1.createLabel();
   }
   private static void createAndShowGUI() {
        JFrame frame = new JFrame("Stack Overflow");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        event1();
        Main newContentPane = new Main();
        newContentPane.add(eventText);
        newContentPane.setOpaque(true);
        frame.setContentPane(newContentPane);
        frame.setSize(1300, 700);
        frame.setVisible(true);
    }
    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();  
            }
        });
    }
    @Override
    public void actionPerformed(ActionEvent arg0) {
        // TODO Auto-generated method stub

    }
}


package package1;

import javax.swing.*;

public class event1 extends JPanel {
    protected static JLabel event1EventText;
    protected static JLabel createLabel(){
         event1EventText = new JLabel();
         event1EventText.setText("Some text");
         return event1EventText;
    }
}

Answer 3

Your question is a little vague and the solution might differ based on more context, however, generally, if you have components in another component, you don't want to allow direct access to them, as it's too easy for other parts your program to do things to them that they really shouldn't be doing.

Instead, one approach is to provide setters and getters to change the state of the label indirectly, for example...

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test100 {

    public static void main(String[] args) {
        new Test100();
    }

    public Test100() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                TestPane pane = new TestPane();
                pane.setLabelText("Look, I'm a label on another panel");

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(pane);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private JLabel label;

        public TestPane() {
            setLayout(new GridBagLayout());
            label = new JLabel();
            add(label);
        }

        public void setLabelText(String text) {
            label.setText(text);
        }

    }

}