Java Applet 通过用户输入绘制形状

Question

这就是我想做的。有一个文本字段，用户输入他想要的内容。例如“矩形”或“矩形”、“圆形”或“圆形”之类的。然后用户按下按钮。之后该程序绘制用户在下面写下的形状。我无法使用“绘画”功能本身。不知怎的，情况变得更糟了。所以我使用了“paintRec”等。但我认为根据OOP，这不是真的。所以请告诉我解决这个问题的合法方法。那里有很多错误的编码。这是肯定的。告诉我如何才能做到这一点。我哪里做错了。谢谢。

public class extends Applet implements ActionListener{
TextField tf;
Button draw;

public void init(){
    tf = new TextField(10);
    draw = new Button("Draw");
    draw.addActionListener(this);
    add(tf);
    add(draw);
}

public void actionPerformed(ActionEvent e) {
    String shape = tf.getText();
    if (shape.equals("rectangle") || shape.equals("RECTANGLE"))
    {
        paintRec(null);
    }
    if (shape.equals("circle") || shape.equals("CIRCLE"))
    {
        paintCirc(null);
    }
}

public void paintRec(Graphics g){
    g.drawRect(30,30,50,60);
}
public void paintCirc(Graphics g){
    g.drawOval(30, 30, 50, 60);
}
}

Answer 1

问题出在这里:

public void actionPerformed(ActionEvent e) {
  String shape = tf.getText();
  if (shape.equals("rectangle") || shape.equals("RECTANGLE"))
  {
    paintRec(null);//passing null value to a method which has Graphics class instance and using it for drawing
  }
  if (shape.equals("circle") || shape.equals("CIRCLE"))
  {
      paintCirc(null);//same here
  }
}

更好的方法是始终使用paint()方法并调用repaint()方法。使用下面的代码:

import java.applet.Applet;
import java.awt.event.*;
import java.awt.*;

/*
<applet code = "Demo.class" width = 400 height = 200> </applet>
*/

public class Demo extends Applet implements ActionListener{
  TextField tf;
  Button draw;
  String shape = "rectangle";//drawing rectangle by default

  public void init(){
    tf = new TextField(10);
    draw = new Button("Draw");
    draw.addActionListener(this);
    add(tf);
    add(draw);
  }

  public void actionPerformed(ActionEvent e) {
    shape = tf.getText();
    repaint();
  }

  public void paint(Graphics g){
    super.paint(g);
    if (shape.equals("rectangle") || shape.equals("RECTANGLE"))
    {
      g.drawRect(30,30,50,60);
    }
    if (shape.equals("circle") || shape.equals("CIRCLE"))
    {
      g.drawOval(30, 30, 50, 60);
    }
    else
    {
      //notify to enter the correct input
    }
  }
}