从屏幕Java清除所有图形

Question

I'm working on a small game and I want to set the condition for defeat. If defeat is true, I want all the graphics on the screen to be cleared so I can make way for some output text on the screen.

I would assume there is a conventional way to do this (which I would rather know than having to put in unnecessary code). Thanks in advance!

Here is my code so far:

public void paintComponent(Graphics g){
        if (!defeat){
            super.paintComponent(g);
            square.display(g);
            wall.display(g);
            for (Circle circle: circleArray){

                circle.display(g);
            }

        }else if(defeat){

            g.drawString("You have been defeated", 300, 300);
        }

Answer 1

You should always call super.paintComponent(g); (unless you really know what you are doing).

Put that call outside your if-statement. That call is what "clears the screen". Like this:

public void paintComponent(Graphics g){
    super.paintComponent(g);
    if (!defeat){
        square.display(g);
        wall.display(g);
        for (Circle circle: circleArray){

            circle.display(g);
        }

    }else if(defeat){

        g.drawString("You have been defeated", 300, 300);
    }

Answer 2

"I want all the graphics on the screen to be cleared so I can make way for some output text on the screen" , but you also want the screen to be cleared every frame, so you basically need to always clear it, meaning you should put super.paintComponent(g); outside any if statements.
I'd recommend this code: (I've cleaned it up and moved the frame clear)

public void paintComponent(Graphics g){
    super.paintComponent(g);
    if (defeat){
        g.drawString("You have been defeated", 300, 300);
    } else {
        square.display(g);
        wall.display(g);
        for (Circle circle: circleArray)
            circle.display(g);
    }
}

I'd also recommend changing the variable defeat to defeated and giving the Graphics object a better name, like I use canvas .