Java - 未存儲值的對象數組（範圍？）

Question

我試圖獲取要渲染爲遊戲畫面的對象數組。我環顧四周，發現了其他人提出的類似問題，但我似乎無法將他們得到的答案應用到我的程序中。

該問題似乎發生在嵌套的for-loops中。在試圖解決這個問題時，我在那些for循環的第一行中得到了Java NullPointerExceptions。

package com.frfanizz.agility; 

import com.badlogic.gdx.Gdx; 
import com.badlogic.gdx.Input.Keys; 
import com.badlogic.gdx.Screen; 
import com.badlogic.gdx.graphics.GL30; 
import com.badlogic.gdx.graphics.OrthographicCamera; 
import com.badlogic.gdx.graphics.g2d.SpriteBatch; 

public class GameScreen implements Screen { 

AgilityGame game; 
OrthographicCamera camera; 

SpriteBatch batch; 
Hero hero; 
Spark[] sparkArray; 
int totalSparks; 

public GameScreen(AgilityGame game) { 
    this.game = game; 
    camera = new OrthographicCamera(); 
    camera.setToOrtho(true, 1920, 1080); 

    batch = new SpriteBatch(); 

    hero = new Hero(60,540); 

    //Variables to set spark array 
    int screenX = 1400; 
    int screenY = 1200; 
    int numOfRow = 11; 
    int numOfCol = 8; 
    float spacingRow = screenY/(numOfRow + 1); 
    float spacingCol = screenX/(numOfCol + 1); 
    int totalSparks = numOfRow*numOfCol; 
    //Spark array 
    Spark[] sparkArray = new Spark[totalSparks]; 
    //setting bounds for sparks 
    int index = 0; 
    for (int i=0;i<numOfCol;i++) { 
     for (int j=0; j<numOfRow;j++) { 
      //sparkArray[index] = new Spark(); 
      sparkArray[index].bounds.x = (float) (60 + spacingCol + ((i)*spacingCol)); 
      sparkArray[index].bounds.y = (float) (spacingRow + ((j-0.5)*spacingRow)); 
      index++; 
     } 
    } 

} 

@Override 
public void render(float delta) { 

    Gdx.gl.glClearColor(1F, 1F, 1F, 1F); 
    Gdx.gl.glClear(GL30.GL_COLOR_BUFFER_BIT); 
    camera.update(); 
    generalUpdate(); 

    batch.setProjectionMatrix(camera.combined); 

    batch.begin(); 

     //Rendering code 
     batch.draw(Assets.spriteBackground, 0, 0); 
     batch.draw(hero.image,hero.bounds.x,hero.bounds.y); 

     for (int i=0; i<totalSparks; i++) { 
      batch.draw(sparkArray[i].image,sparkArray[i].bounds.x,sparkArray[i].bounds.y); 
     } 

    batch.end(); 

} 

//Other gamescreen methods 

} 

的類英雄和星火如下：

package com.frfanizz.agility; 

import com.badlogic.gdx.graphics.g2d.Sprite; 
import com.badlogic.gdx.math.Rectangle; 

public class Hero { 

public Sprite image; 
public Rectangle bounds; 

public Hero(int spawnX, int spawnY) { 
    image = Assets.spriteHero; 
    image.flip(false, true); 
    bounds = new Rectangle(spawnX - 16, spawnY - 16, 32, 32); 
} 
} 

和：

package com.frfanizz.agility; 

import com.badlogic.gdx.graphics.g2d.Sprite; 
import com.badlogic.gdx.math.Rectangle; 

public class Spark { 

public Sprite image; 
public Rectangle bounds; 

public Spark() { 
    image = Assets.spriteSpark; 
    image.flip(false, true); 
    bounds = new Rectangle(); 
    bounds.height = 32; 
    bounds.width = 32; 
} 
} 

在for循環中，我已經印刷sparkArray的價值，所以我想我有值的問題，而不是我已閱讀答案的其他問題的參考。 （這裏是我（失敗）引用的問題： Java. Array of objects， Java NullPointerException with objects in array）提前

謝謝！

Answer 1

取消對該行

//sparkArray[index] = new Spark(); 

你的星火對象的數組包含空值，直到你把星火的情況下進去。

考慮使用Spark的二維數組，如果它適合您正在做的事情。

int numOfRow = 11; 
int numOfCol = 8; 
Spark[][] sparkArray = new Spark[numOfRow][numOfCol]; 
//setting bounds for sparks 
for (int row=0; row<numOfRow; row++) { 
    for (int col=0; col<numOfCol; col++) { 
     sparkArray[row][col] = new Spark(); 
     sparkArray[row][col].bounds.x = 1.23; // example of usage 
    } 
}