如何在JFrame上绘制文本并用Java清除? [英] How to drawing a text on JFrame and clearing in java?

问题描述

我想在键盘上按'h'时使用drawString方法在JFrame上绘制文本，而在键盘上按'c'时清除文本，这是我的代码，可以用于绘制，但是我不知道不知道该如何工作.

I want to draw a text on the JFrame using drawString method when I press 'h' on the keyboard and clear the text when I press 'c' on the keyboard this is my code, it is working for drawing but I don't know how to work for clear.

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class test extends JPanel implements KeyListener {

char help,clear;
    public test() {
        super();
        setFocusable(true);
        this.addKeyListener(this);
    }

    //********************************************************************
       public void paintComponent(Graphics g) {
      repaint();
         g.setColor(Color.red);
         g.drawString("press 'H' for help ",150,50);

    if(help=='h'){
         g.drawString("one",150,100);
        }//end id help

if(clear=='c'){
                 g.drawString("",150,100);
        }//end id clear
    }

 //******************keyyyyyyy******************************************

     public void keyPressed(KeyEvent e) {

    if(e.getKeyChar()=='h'){
        help='h';
    }
if(e.getKeyChar()=='c'){
        clear='c';
    }
    }
     public void keyReleased(KeyEvent e) {
    }
 public void keyTyped(KeyEvent e) {
     }
    //********************************************************************
    public static void main(String[] args) {
        test panel=new test();
         JFrame frame = new JFrame("java lover");
       frame.add(panel);
       frame.setSize(400,400);
              frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    }
}

感谢您的帮助.

推荐答案

g.drawString("",150,100);

与擦除"先前的图形相反，它什么也没画.

That would draw nothing, as opposed to 'erasing' the previous drawing.

public void paintComponent(Graphics g) {
  repaint();

那将导致无限循环.应该是:

That would cause an infinite loop. It should be:

 public void paintComponent(Graphics g) {
  super.paintComponent(g); // paint the BACKGROUND and borders

这样做，原始字符串将被删除.

Doing it this way, the original string will be erased.

一般提示:对于Swing，通常在基于AWT的较低级别的 KeyListener 上使用键绑定.有关如何使用键绑定的详细信息，请参见如何使用键绑定.

As a general tip: For Swing, typically use key bindings over the AWT based, lower level, KeyListener. See How to Use Key Bindings for details on how to use them.

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