Question

import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.geom.Point2D;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Line2D;

public class Car {

private int xLeft;
private int yTop;

public Car(int x, int y){
    xLeft =x;
    yTop=y;
}

public void draw(Graphics2D g2){
    Rectangle body = new Rectangle(xLeft, yTop+10, 60, 10);
    Ellipse2D.Double frontTire= new Ellipse2D.Double(xLeft+10, yTop+20, 10,     10);
     Ellipse2D.Double rearTire= new     Ellipse2D.Double(xLeft+40,yTop+20,10,10);
    Point2D.Double r1 = new Point2D.Double(xLeft+10,yTop+10);
    Point2D.Double r2 = new Point2D.Double(xLeft+20,yTop);
    Point2D.Double r3 = new Point2D.Double(xLeft+40,yTop);
    Point2D.Double r4 = new Point2D.Double(xLeft+50,yTop+10);
    Line2D.Double frontWindshield = new  Line2D.Double(r1,r2);
    Line2D.Double roofTop = new  Line2D.Double(r2,r3);
    Line2D.Double rearWindshield = new  Line2D.Double(r3,r4);

    g2.draw(body);
    g2.draw(frontTire);
    g2.draw(rearTire);
    g2.draw(frontWindshield);
    g2.draw(roofTop);
    g2.draw(rearWindshield);
 }
}

import java.awt.Graphics;
import java.awt.Graphics2D;

import javax.swing.JComponent;

public class CarComponent extends  JComponent {
public void paintCompnent(Graphics g){
    Graphics2D g2 = (Graphics2D) g;
    Car car1 = new Car(0,0);
     int x = getWidth()-60;
     int y = getHeight()-30;

     Car car2 = new Car(x,y);
     car1.draw(g2);
     car2.draw(g2);
 }
}

import javax.swing.JFrame;
public class CarViewer {

     public static void main(String[] args) {
    JFrame frame = new JFrame();
    frame.setSize(400,500);
    frame.setTitle("Two Cars");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    CarComponent component = new CarComponent();
    frame.add(component);

    frame.setVisible(true);
    }

 }

我已经看了几个小时的代码，但无法弄清楚出了什么问题。它被复制出教科书。当我跑步时，只显示一个空盒子。它应该显示汽车，一个在左上角，一个在右下角。

Answer 1

方法paintComponent拼写错误，因此它不会覆盖超类方法。因此，只调用绘制空白框的默认方法。

通过@Override注释，有一种方法可以避免这种常见错误。通过将此注释添加到覆盖超类方法或实现接口方法的所有方法，如果您输入方法名称错误，编译器将停止并显示错误，而不是创建难以调试的错误：

@Override
public void paintComponent(Graphics g){
    // code here
}

我的GUI程序有什么问题

1 个答案: