Question

所以这个程序的目的是创建一个椭圆和一个按钮，当你点击它时，椭圆会改变颜色。颜色的顺序应该是红色，然后是绿色，然后是蓝色。我该如何创建这个循环？我是否使用for循环？这是我没有循环的代码：

public class ButtonButton implements java.awt.event.ActionListener{

   private NscWindow win;
   private NscEllipse oval;

   public ButtonButton() {
     win = new NscWindow();
     win.setTitle("ButtonButton");
     oval = new NscEllipse(100, 70, 200, 150);
     oval.setFilled(true);
     oval.setBackground(java.awt.Color.blue);

     javax.swing.JButton btn;
     btn = new javax.swing.JButton("click me");
     win.add(oval);
     btn.setSize(170, 35);
     btn.setLocation(110, 10);
     win.add(btn);
     win.repaint();
     btn.addActionListener(this);

  }
   public void actionPerformed(java.awt.event.ActionEvent e) {
     win.setTitle("Thanks, I needed that");
     javax.swing.JButton btn;
     btn = (javax.swing.JButton)e.getSource();
     btn.setText("Thanks, I needed that");
     oval.setBackground(java.awt.Color.green);
     win.repaint();
  }

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

Answer 1

为了循环每个，做这样的事情：

 public void actionPerformed(java.awt.event.ActionEvent e) {
     win.setTitle("Thanks, I needed that");
     javax.swing.JButton btn;
     btn = (javax.swing.JButton)e.getSource();
     btn.setText("Thanks, I needed that");

     if (oval.getBackground().equals(java.awt.Color.red))
         oval.setBackground(java.awt.Color.green);
     else if (oval.getBackground().equals(java.awt.Color.green))
         oval.setBackground(java.awt.Color.blue);
     else if (oval.getBackground().equals(java.awt.Color.blue))
         oval.setBackground(java.awt.Color.red);
     win.repaint();
}

Answer 2

首先创建一个颜色数组......

public static final Color COLORS[] = new Color[]{Color.RED, Color.GREEN, Color.BLUE};

提供某种价值来追踪你最喜欢的颜色......

private int colorIndex = -1;

添加一种方便的方法来改变颜色......

public void applyNextColor() {
    colorIndex++;
    if (colorIndex >= COLORS.length) {
        colorIndex = 0;
    }
    oval.setBackground(COLORS[colorIndex]);
}

然后在构造函数中初始化初始颜色......

public ButtonButton() {
    win = new NscWindow();
    win.setTitle("ButtonButton");
    oval = new NscEllipse(100, 70, 200, 150);
    oval.setFilled(true);
    nextColor();

    //...
}

然后在你的动作监听器中，只需应用下一个颜色......

public void actionPerformed(java.awt.event.ActionEvent e) {
    win.setTitle("Thanks, I needed that");
    // This is a NullPointerException waiting to happen...
    //javax.swing.JButton btn;
    btn = (javax.swing.JButton)e.getSource();
    btn.setText("Thanks, I needed that");
    applyNextColor();
    win.repaint();
}

您可以使用enum和/或模块化数学执行相同的操作，但这样可以保持简单;）

如何更新点击处理程序，使其循环显示三种颜色：红色，绿色和蓝色？

2 个答案: