java - boolean 值不适用于图形 java

Question

这是我的代码

package javaapplication7;

import java.awt.*;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import javax.swing.*;

import java.awt.Graphics;

import java.awt.Graphics2D;``

import java.util.*;

import java.io.*;

public class JavaApplication7 extends JPanel implements ActionListener{

    JButton j = new JButton();

    boolean drawHello = true;

    boolean drawWorld = false;

   String hello = "Hello";

   String World = "World";


   public JavaApplication7(){

       this.setLayout(new BorderLayout());

        add(j,BorderLayout.NORTH);

    }

    public void actionPerformed(ActionEvent e) {

     boolean drawWorld = true;

      repaint();
}

    protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    if (drawHello)
             g.drawString(hello, 50, 50);

    if (drawWorld)
             g.drawString(World, 70, 70);
}



    public static void main(String[] args) {
        JFrame f = new JFrame("Swing Paint Demo");
        JavaApplication7 j7 = new JavaApplication7();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setSize(250,250);
        f.setVisible(true);
        f.add(j7);
    }

}

Answer 1

我不明白的是您定义了一个 Boolean 然后在 actionPerformed() 中创建了另一个，只需删除 Boolean 如下:

public void actionPerformed(ActionEvent e) {

drawWorld = true;

  repaint();
}

因为你已经在那里创建了它:

public class JavaApplication7 extends JPanel implements ActionListener{

JButton j = new JButton();

boolean drawHello = true;

boolean drawWorld = false; //<------

同时添加

j.addActionListener(this);

像这样:

public JavaApplication7(){

   this.setLayout(new BorderLayout());
   j.addActionListener(this);
   add(j,BorderLayout.NORTH);

}