[英]Changing the Traffic Lights with If or Switch Statements
我很想为我的Java编程入门课程编程交通信号灯仿真。 当我运行该applet时,即使我还没有单击任何JButton,所有三个指示灯仍然点亮。 当我这样做时,小程序确实会像做某事一样暂时变空白,如果我按GO,则汽车确实会移动。 我想知道是否需要重置图形类中的颜色,还是使用switch语句(我不确定如何做)并以一种颜色开始,如我在其他示例中所看到的那样。 我的代码中是否有任何不正确的东西妨碍我获得想要的结果? 任何帮助将不胜感激。 谢谢。
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
/**
* Class TrafficLights - At the click of a button, change the traffic lights
*
* @author Mickey Mouse
* @version JDK 8
* @course CSCI 1130-01
* @date 10-2-15
*/
public class TrafficLights extends JApplet implements ActionListener {
private JButton WAIT, STOP, GO;
private boolean clickWAIT = false;
private boolean clickSTOP = false;
private boolean clickGO = false;
private int carX = 200;
/**
* Called by the browser or applet viewer to inform this JApplet that it
* has been loaded into the system. It is always called before the first
* time that the start method is called.
*/
public void init()
{
setLayout( new FlowLayout()); // changes the layout from BorderLayout to FlowLayout
WAIT = new JButton ("WAIT"); //adds WAIT label to button
WAIT.setForeground(Color.yellow); //changes the label to yellow
//adds the WAIT JButton to the screen
add (WAIT);
WAIT.addActionListener(this);
GO = new JButton ("GO"); //adds GO label to button
GO.setForeground(Color.green); //changes the label to green
//adds the button to the screen
add (GO);
GO.addActionListener(this);
STOP = new JButton ("STOP"); //adds STOP label to button
STOP.setForeground(Color.red); //changes the label to red
//adds STOP JButton to screen
add (STOP);
STOP.addActionListener(this);
}
/**
* Called by the browser or applet viewer to inform this JApplet that it
* should start its execution. It is called after the init method and
* each time the JApplet is revisited in a Web page.
*/
public void start()
{
// provide any code requred to run each time
// web page is visited
}
/**
* Called by the browser or applet viewer to inform this JApplet that
* it should stop its execution. It is called when the Web page that
* contains this JApplet has been replaced by another page, and also
* just before the JApplet is to be destroyed.
*/
public void stop()
{
// provide any code that needs to be run when page
// is replaced by another page or before JApplet is destroyed
}
/**
* Paint method for applet.
*
* @param g the Graphics object for this applet
*/
public void paint(Graphics g)
{
super.paint(g);
//declares and retrieves the images from their file locations
Image img = getImage(getDocumentBase(), "stoplights.png");
Image img2 = getImage(getDocumentBase(), "car.jpg");
g.drawImage( img, 50, 100, 300, 350, 0, 0, 5000, 5000, this ); //draws and resizes the stoplights image
g.drawImage( img2, carX, 400, 1000, 1000, 0, 0, 5000, 5000, this); //draws and resizes the car image
//draw and fill an oval red for the STOP stoplight when STOP is pressed
if (clickSTOP == true);
{
g.drawOval(63, 112, 30, 30);
g.setColor(Color.red);
g.fillOval(63, 112, 30, 30);
clickSTOP = false;
}
//draw and fill an oval yellow for the WAIT stoplight when WAIT is pressed
if (clickWAIT == true);
{
g.setColor(Color.black);
g.drawOval(63, 148, 30, 30);
g.setColor(Color.orange);
g.fillOval(63, 148, 30, 30);
clickWAIT = false;
}
//draw and fill an oval green for the GO stoplight when GO is pressed
if (clickGO == true);
{
g.setColor(Color.black);
g.drawOval(63, 184, 30, 30);
g.setColor(Color.green);
g.fillOval(63, 184, 30, 30);
clickGO = false;
}
}
public void actionPerformed(ActionEvent event)
{
/*
* Links the JButtons and the graphic sequences to display the lights
*
*/
if(event.getSource() == GO) //display green if GO is clicked
{
clickGO = true;
carX -=15;
repaint();
}
if (event.getSource() == WAIT) //display yellow if WAIT is clicked
{
clickWAIT = true;
repaint();
}
if (event.getSource() == STOP) //display red if STOP is clicked
{
clickSTOP = true;
repaint();
}
}
/**
当我运行该applet时,即使我还没有单击任何JButton,所有三个指示灯仍然点亮
这是因为你有一个;
在每个if
语句之后,这基本上使逻辑短路,因此无论变量的状态如何,始终执行其后的代码...
if (clickSTOP == true);
因此,相反,您应该使用更像
if (clickSTOP == true)
{
g.setColor(Color.red);
g.fillOval(63, 112, 30, 30);
clickSTOP = false;
}
您还可以从paint
方法内部修改程序的状态,通常不建议这样做,因为paint
应该这样做,就可以绘制当前状态。
更改状态的更好位置是在ActionListener
。
您应该拥有一个状态变量,而不是拥有三个通常描述同一件事的状态变量,因此状态只能是go
或wait
或stop
,而不能是所有这三个状态的组合。
同样,您可以使用ButtonGroup
和JToggleButton
或JRadioButton
,这将允许按钮携带一定数量的有关状态的信息,因为一次只能选择一个按钮。
看一下如何使用ButtonGroup组件以及如何使用按钮,复选框和单选按钮以获取更多详细信息。
当我这样做时,小程序确实会像做某事一样暂时变成空白
这可能是由于您是从paint
方法中加载图像而导致的,但通常,应避免覆盖此类顶级容器的paint
。
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