在 Java 中移動 GObject 的問題

Question

我有一個矩形 GObject 我想在屏幕上跟隨鼠標。 如果移動它，它當前會留下一條黑線，因為程序不會刪除任何先前的矩形。 代碼如下

// TODO: comment this program

import acm.graphics.*;     // GOval, GRect, etc.
import acm.program.*;      // GraphicsProgram
import acm.util.*;         // RandomGenerator
import java.awt.*;         // Color
import java.awt.event.*;   // MouseEvent

public class Breakout extends BreakoutProgram {

    public void run() {

        // Set the canvas size.  In your code, remember to ALWAYS use getWidth()
        // and getHeight() to get the screen dimensions, not these constants!
        setCanvasSize(CANVAS_WIDTH, CANVAS_HEIGHT);
        
        // TODO: finish this program
        brickBuilder();


    }
    
    //This method creates the bricks in the program. It will also set the color for the bricks. 
    //Input: The constants for brick columns,brick width,brick separation, brick y offset, brick height,brick columns and brick rows
    //Output: The brick display
    private void brickBuilder() {
        int i=0;//i will count columns
        int j=-1;//j will count rows, set to -1 or the color display will break as well as y-coordinate
        while(j<(NBRICK_ROWS-1)) {
            j++;
            i-=i;//i must reset or while loop will only execute once for columns
            double x_coordinate = getWidth()/2-(NBRICK_COLUMNS*BRICK_WIDTH+((NBRICK_COLUMNS-1)*BRICK_SEP))/2;
            double y_coordinate = BRICK_Y_OFFSET;
            y_coordinate +=j*(BRICK_HEIGHT+BRICK_SEP);
            while(i<NBRICK_COLUMNS) {
                i++;
                x_coordinate +=(BRICK_WIDTH+BRICK_SEP);
                GRect brickWall = new GRect(x_coordinate,y_coordinate,BRICK_WIDTH,BRICK_HEIGHT);
                brickWall.setFilled(true);
                switch((j+1)%10) {//switch will set the color, uses remainder to decide color of brick
                case 1:
                    brickWall.setFillColor(Color.RED);
                    break;
                case 2:
                    brickWall.setFillColor(Color.RED);
                    break;
                case 3:
                    brickWall.setFillColor(Color.ORANGE);
                    break;
                case 4:
                    brickWall.setFillColor(Color.ORANGE);
                    break;
                case 5:
                    brickWall.setFillColor(Color.YELLOW);
                    break;
                case 6:
                    brickWall.setFillColor(Color.YELLOW);
                    break;
                case 7:
                    brickWall.setFillColor(Color.GREEN);
                    break;
                case 8:
                    brickWall.setFillColor(Color.GREEN);
                    break;
                case 9:
                    brickWall.setFillColor(Color.CYAN);
                    break;
                case 0:
                    brickWall.setFillColor(Color.CYAN);
                    break;
                }
                add(brickWall);
                }
        
}
        }
    
    public void mouseMoved(MouseEvent e) {
        GRect paddle = new GRect(e.getX(), getHeight()-PADDLE_Y_OFFSET, PADDLE_WIDTH, PADDLE_HEIGHT);
        paddle.setFilled(true);
        add(paddle);

    }
    
    public void init() {
        addMouseListeners();
        
    }
}

我哪里錯了？ 據我所知，問題在於 mousemoved 和 init 類。

Answer 1

我想到了。 必須將鼠標監聽器添加到 mouseMoved 方法中，並且必須為鼠標監聽器本身創建另一個方法。

// TODO: comment this program

import acm.graphics.*;     // GOval, GRect, etc.
import acm.program.*;      // GraphicsProgram
import acm.util.*;         // RandomGenerator
import java.awt.*;         // Color
import java.awt.event.*;   // MouseEvent

public class Breakout extends BreakoutProgram {
    private GRect paddle;
    
    public void run() {
        // Set the window's title bar text
        setTitle("CS 106A Breakout");

        // Set the canvas size.  In your code, remember to ALWAYS use getWidth()
        // and getHeight() to get the screen dimensions, not these constants!
        setCanvasSize(CANVAS_WIDTH, CANVAS_HEIGHT);
        
        // TODO: finish this program
        brickBuilder();
        buildPaddle();


    }
    
    
    
    //This method creates the bricks in the program. It will also set the color for the bricks. 
    //Input: The constants for brick columns,brick width,brick separation, brick y offset, brick height,brick columns and brick rows
    //Output: The brick display
    private void brickBuilder() {
        int i=0;//i will count columns
        int j=-1;//j will count rows, set to -1 or the color display will break as well as y-coordinate
        while(j<(NBRICK_ROWS-1)) {
            j++;
            i-=i;//i must reset or while loop will only execute once for columns
            double x_coordinate = getWidth()/2-(NBRICK_COLUMNS*BRICK_WIDTH+((NBRICK_COLUMNS-1)*BRICK_SEP))/2;
            double y_coordinate = BRICK_Y_OFFSET;
            y_coordinate +=j*(BRICK_HEIGHT+BRICK_SEP);
            while(i<NBRICK_COLUMNS) {
                i++;
                x_coordinate +=(BRICK_WIDTH+BRICK_SEP);
                GRect brickWall = new GRect(x_coordinate,y_coordinate,BRICK_WIDTH,BRICK_HEIGHT);
                brickWall.setFilled(true);
                switch((j+1)%10) {//switch will set the color, uses remainder to decide color of brick
                case 1:
                    brickWall.setFillColor(Color.RED);
                    break;
                case 2:
                    brickWall.setFillColor(Color.RED);
                    break;
                case 3:
                    brickWall.setFillColor(Color.ORANGE);
                    break;
                case 4:
                    brickWall.setFillColor(Color.ORANGE);
                    break;
                case 5:
                    brickWall.setFillColor(Color.YELLOW);
                    break;
                case 6:
                    brickWall.setFillColor(Color.YELLOW);
                    break;
                case 7:
                    brickWall.setFillColor(Color.GREEN);
                    break;
                case 8:
                    brickWall.setFillColor(Color.GREEN);
                    break;
                case 9:
                    brickWall.setFillColor(Color.CYAN);
                    break;
                case 0:
                    brickWall.setFillColor(Color.CYAN);
                    break;
                }
                add(brickWall);
                }
        
}
        }

    private void buildPaddle() {
    paddle = new GRect(0, getHeight()-PADDLE_Y_OFFSET, PADDLE_WIDTH, PADDLE_HEIGHT);
    paddle.setFilled(true);
    add(paddle);
    addMouseListeners();
    }
    
    public void mouseMoved(MouseEvent e) {
       paddle.setLocation(e.getX(), getHeight()-PADDLE_Y_OFFSET);
    }
    
    
    
}

我看了https://github.com/NatashaTheRobot/Stanford-CS-106A ，因為我完全被難住了，並學習了新的 setLocation 方法。