Java如何制作可以通过单击按钮绘制的形状

Question

im creating a 2d world which has a player that is in a rectangle shape and what im trying to do is when the player press space button it draws a block depending on his direction the problem is it only sets for one block and plus it deletes it after repaiting now i know my mistake is in paint method. what i wanna know how to make it draws the block everytime i press space without removing after repainting and can be set for multiple times i know i should use loop but i dont know exactly i should write it

private static final long serialVersionUID = -1401667790158007207L;
int playerx = 450;
int playery = 450;
int playerDirection = 0;      //north = 0, west = 1, south = 2, east = 3
boolean setBlock;

public platform(){
    super("2D game");

    JPanel panel = new JPanel();
    panel.setBackground(Color.white);

    addKeyListener(this);
    this.setContentPane(panel);
}

public void paint(Graphics g){
    super.paint(g);
    Graphics2D g2 = (Graphics2D)g;

    Rectangle player = new Rectangle(playerx, playery, 50, 50);
    g2.fill(player);

    if(setBlock){

        if(playerDirection == 0){

            g2.fillRect(playerx, playery - 50, 50, 50);
        }else if(playerDirection == 1){

            g2.fillRect(playerx + 50, playery, 50, 50);
        }else if(playerDirection == 2){

            g2.fillRect(playerx, playery + 50, 50, 50);
        }else if(playerDirection == 3){

            g2.fillRect(playerx - 50, playery, 50, 50);
        }

        setBlock = false;
    }
}

public void keyPressed(KeyEvent e) {

    if(e.getKeyCode() == KeyEvent.VK_UP){

        playerDirection = 0;
        playery -=50;
        repaint();
    }
    if(e.getKeyCode() == KeyEvent.VK_DOWN){

        playerDirection = 2;
        playery +=50;
        repaint();
    }
    if(e.getKeyCode() == KeyEvent.VK_RIGHT){

        playerDirection = 1;
        playerx += 50;
        repaint();
    }
    if(e.getKeyCode() == KeyEvent.VK_LEFT){

        playerDirection = 3;
        playerx -=50;
        repaint();
    }
    if(e.getKeyCode() == KeyEvent.VK_SPACE){

        setBlock = true;
    }
}

public void keyReleased(KeyEvent e) {


}

public void keyTyped(KeyEvent e) {


}

}

Answer 1

You need to store your Blocks in a List. And add a new one when pressing Space Key. Then you can easily draw all of them in a for loop. Also remove that setBlock boolean because it makes no sense.

...
// introduce this class to hold a block
class Block{
    public int x;
    public int y;
    public Block(int _x, int _y){
        x = _x;
        y = _y;
    }
}
...
// boolean setBlock;  // remove this boolean
ArrayList<Block> blocks = new ArrayList<Block>();  // list of all blocks

public platform(){...}

public void paint(Graphics g){
    ...    
    // if(setBlock){  // remove this boolean

        if(playerDirection == 0){
            g2.fillRect(playerx, playery, 50, 50);
        }else if(playerDirection == 1){
            g2.fillRect(playerx, playery, 50, 50);
        }else if(playerDirection == 2){
            g2.fillRect(playerx, playery, 50, 50);
        }else if(playerDirection == 3){
            g2.fillRect(playerx, playery, 50, 50);
        }
        // draw the blocks
        for(Block b : blocks)
            g2.fillRect(b.x, b.y, 50, 50);

        // setBlock = false; // remove this boolean
    //}  // remove this boolean
}

public void keyPressed(KeyEvent e) {
    ...
    if(e.getKeyCode() == KeyEvent.VK_SPACE){
        // setBlock = true;  // remove this boolean
        // add a new block
        blocks.add(new Block(playerx, playery));
        repaint();
    }
}
...