的NullPointerException在libgdx（Java）的重疊

Question

我做一個簡單的Java遊戲，因爲我的一部分，它性學習的，當我運行它，我得到一個：

Exception in thread "LWJGL Application" java.lang.NullPointerException at com.mattihase.floatingpoint.GameScreen.generalUpdate(GameScreen.java:65) at com.mattihase.floatingpoint.GameScreen.render(GameScreen.java:42) at com.badlogic.gdx.Game.render(Game.java:46) at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:207) at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:114)

這是一般更新線就在談論和它下面的直線：

if(pc.bounds.overlaps(gary.Rbounds)) 
    //where i test a bunch of booleans to see what the dialog returned should be 
    //yes, i know i'm probably doing the ifs it unoptimized but i couldn't get it to 
    //work the other way. 
    //the pc.bounds stuff is there to make it follow the player character around the 
    //world as the camera already does this. 
     { 
     if(pc.onquest = false){ 
      if(pc.finishquest = false){ 
      Assets.font.draw(batch, gary.Gdio, pc.bounds.x - 250, pc.bounds.y - 190); 
      pc.onquest = true; 
      } 
     } 
     if(pc.onquest = true){ 
      if(pc.finishquest = false){ 
      Assets.font.draw(batch, gary.GDdio, pc.bounds.x - 250, pc.bounds.y - 190); 
      } 
      } 
     if(pc.haspoints = true){ 
      pc.finishquest = true; 
     } 
     if(pc.finishquest = true); 
     Assets.font.draw(batch, gary.GCdio, pc.bounds.x - 250, pc.bounds.y - 190); 
     pc.onquest = false; 
     pc.award = true; 
    }` 

和這些都爲playercharacter和NPC（稱爲PC（類playerCharacter）和加里類（CLA SS Rectoid）分別） 玩家角色

public Sprite image; 
public Rectangle bounds; 
public int score; 
public String scoreprint; 
public boolean onquest; 
public boolean finishquest; 
public boolean haspoints; 
public boolean award; 

public PlayerCharacter(){ 
    onquest = false; 
    haspoints = false; 
    finishquest = false; 
    award = false; 
    score = 0; 
    image = Assets.s_pc; 
    bounds = new Rectangle(256-16, 192-16, 16, 16); 
    scoreprint = score + "";` 

和加里 '公共雪碧銳美; public Rectangle Rbounds; public String Gdio; public String GDdio; public String GCdio;

public Rectoid() 
{ 
    Rimage = Assets.s_rectoid; 
    Rbounds = new Rectangle(1024, 64, 64, 32); 
    Gdio = "the diolog"; 
    GDdio = "the diolog"; 
    GCdio = "the diolog";` 

Ç

Answer 1

在Java中，檢查平等對象的引用或基本類型，你必須使用==運營商。在if(pc.onquest = false){這樣的行中，您將false指定爲onquest，而不是檢查其值。 代碼編譯的原因是因爲在Java中，賦值返回賦值。 例如上一句：

int zero = 0; 
if (zero == 0){} //its true 
if (zero = 0){} //compile error, becouse 'zero = 0' returns '0', the asigned value 

什麼在你的代碼的情況是，您使用的布爾變量。

if(pc.bounds.overlaps(gary.Rbounds)) 
    { 
    if(pc.onquest = false){ // HERE YOU ARE DOING TWO THINGS: assing false to 
          // onquest and return false. The following code is never execute 
     if(pc.finishquest = false){ // SAME HERE 
     Assets.font.draw(batch, gary.Gdio, pc.bounds.x - 250, pc.bounds.y - 190); 
     pc.onquest = true; 
     } 
    } 
    if(pc.onquest = true){// SAME HERE 
     if(pc.finishquest = false){// SAME HERE 
     Assets.font.draw(batch, gary.GDdio, pc.bounds.x - 250, pc.bounds.y - 190); 
     } 
     } 
    if(pc.haspoints = true){// SAME HERE 
     pc.finishquest = true; 
    } 
    if(pc.finishquest = true);// SAME HERE 
    Assets.font.draw(batch, gary.GCdio, pc.bounds.x - 250, pc.bounds.y - 190); 
    pc.onquest = false; 
    pc.award = true; 
}` 

此外，檢查一個布爾值只是用它，沒有把它比作真或假，並利用!運營商。

只是簡單的使用if(!pc.onquest){如果你想檢查是否禁用了onquest。

關於NullPointerEception，可能gary變量爲null。檢查你之前是否創建過它。它應該是這樣的：

Rectoid gary = new Rectoid();