Java 为什么玩家会倍增？

下面的示例代码分为两个类：World和Driver 世界级：

public class World {

    private char[][] world2D;
    private int characterRow;
    private int characterColumn;
    private int score;
    private int collision = 0;

    public World(int width, int height){
        world2D = new char[width][height];
        characterColumn = 0;
        characterRow = 0;

        for(int i = 0; i < world2D.length; i++){
            for(int j = 0; j < world2D[i].length; j++){
                world2D[i][j] = '-';
            }
        }

        world2D[characterRow][characterColumn] = 'P';
    }

    public void moveUp(){
        world2D[characterRow][characterColumn] = '-';
        if (characterRow > 0){
            characterRow -= 1;
        }
        world2D[characterRow][characterColumn] = 'P';
        score ++;
    }

    public void moveDown(){
        world2D[characterRow][characterColumn] = '-';
        if (characterRow < world2D.length){
            characterRow += 1;
        }
        world2D[characterRow][characterColumn] = 'P';
        score ++;
    }

    public void moveRight(){
        world2D[characterRow][characterColumn] = '-';
        if (characterColumn < (world2D[characterRow].length - 1)){
            characterColumn += 1;
        }
        world2D[characterRow][characterColumn] = 'P';
        score ++;
    }

    public void moveLeft(){
        world2D[characterRow][characterColumn] = '-';
        if (characterColumn > 0){
            characterColumn -= 1;
        }
        world2D[characterRow][characterColumn] = 'P';
        score ++;
    }
    public int getScore(){
        return score;
    }

    public void displayWorld(){
        for(int i = 0; i < world2D.length; i++){
            for(int j = 0; j < world2D[i].length; j++){
                System.out.print(world2D[i][j]);
            }
            System.out.println();
        }       
    }
    public int getCollision(){
        return collision;
    }

    public int getCharacterRow(){
        return characterRow;
    }

    public void addRock(){
        int lastRow = world2D.length - 1;
        int width = world2D[lastRow].length - 1;
        int rockPosition = (int) (Math.random()*width);
        if (world2D[lastRow][rockPosition] != 'P'){
            world2D[lastRow][rockPosition] = '@';
        }
        if (world2D[lastRow][rockPosition] == 'P'){
            collision = 1;
        }

    }
    public void shiftWorldUp(){
        for(int row = 0; row < world2D.length - 2; row++){
            world2D[row] = world2D[row + 1];
            }
        //world2D[characterRow][characterColumn] = 'P';
    }

}

当我尝试执行代码时，会出现一个奇怪的错误，数组的多个部分都用“p”字符填充，如下所示：

How tall should the world be?: 6
How wide should the world be?: 6
To move type 'up', 'down', 'left' or 'right
P-----
------
------
------
------
------
Next move?: 
down
------
P-----
------
------
------
@-----
Next move?: 
down
P-----
------
P-----
P-----
P-----
@---@-
Next move?: 

---

我找不到这个虫子。这是一个有趣的，所以我希望有人能帮我找到它

当你执行shiftWorldUp时，你不会擦除p？我如何在shiftWorldUp方法中执行该操作？当世界向上移动时，玩家会发生什么情况？带有@符号或“rock”的行应该向上移动到下一行，最下面一行应该填充另一个“rock”

How tall should the world be?: 6
How wide should the world be?: 6
To move type 'up', 'down', 'left' or 'right
P-----
------
------
------
------
------
Next move?: 
down
------
P-----
------
------
------
@-----
Next move?: 
down
P-----
------
P-----
P-----
P-----
@---@-
Next move?: