[英]why is there not a Runtime error when assigning Graphics reference to Graphics2D reference variable in paintComponent method?
[英]Does invoking the drawRect method on a Graphics2D trigger the paintComponent method?
我正在试图找出我的程序的行为,这是我最好的理论,为什么它做它做的事情。 我希望这会使用rand
变量来决定绘制哪个形状,但是看起来paintComponent
方法在计时器点击之间被多次调用,导致许多形状被绘制,我试图理解为什么。
这是代码:
public class TestPane extends JPanel {
private int yPos0;
private int yPos1;
private int boundary0=750;
private ActionEvent ae = null;
private Graphics g0 = null;
private int count=1;
public TestPane(Color foreground){
setForeground(foreground);
this.setBackground(Color.BLUE);
Timer timer = new Timer(3000,new ActionListener(){
@Override
public void actionPerformed(ActionEvent e){
ae = e;
yPos0 =yPos0+50;
repaint();
}
});
timer.start();
}
@Override
public void paintComponent(Graphics g){
g0 = g;
super.paintComponent(g);
createShape(yPos0);
repaint();
}
public void createShape(int ypos0){
//generate random number between 1 and 3 and assign to rand
int rand = (int)((Math.random()*3)+1);
System.out.println(rand);
if(rand==1){
Graphics2D g2d = (Graphics2D) g0.create();
g2d.setColor(Color.RED);
g2d.drawRect(0, ypos0, 200, 50);
}
if(rand==2){
Graphics2D g2d = (Graphics2D) g0.create();
g2d.setColor(Color.GREEN);
g2d.drawRect(0, ypos0, 150, 50);
g2d.drawRect(50, ypos0+50,50,50);
}
}
}
paintComponent
被多次调用的原因是你在该方法中调用repaint
,导致自己被无限地称为ad 。 这不是必需的,因为您已经从Timer
调用repaint
。
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