为什么我不断收到显示java.lang.NullPointerException

Question

我不断收到这个代码显示java.lang.NullPointerException：

private void render(){ 
    BufferStrategy bs = this.getBufferStrategy(); 
    if(bs == null){ 
     this.createBufferStrategy(3); 
    } 

    Graphics g = bs.getDrawGraphics(); 

    g.dispose(); 
    bs.show(); 
} 

谁能告诉我在做什么错？

Answer 1

你应该试试这个：

private void render(){ 
    BufferStrategy bs = this.getBufferStrategy(); 
    if(bs == null){ 
     this.createBufferStrategy(3); 
     bs = this.getBufferStrategy(); // reassign bs 
    } 

    Graphics g = bs.getDrawGraphics(); 

    g.dispose(); 
    bs.show(); 
} 

Answer 2

即使你打电话this.createBufferStrategy(3);您bs变量保持未分配。

你需要创建后读回：

if(bs == null){ 
    this.createBufferStrategy(3); 
    bs = this.getBufferStrategy(); 
} 

它是增加一个检查，以确保的createBufferStrategy通话后，你得到一个非空一个好主意：

this.createBufferStrategy(3); 
bs = this.getBufferStrategy(); 
if (bs == null) throw new IllegalStateException("Buffered structure is not created."); 

Answer 3

您忘记将新的BufferStrategy指定为null以指定给变量bs。将其更改为

if (bs == null) { 
    bs = this.createBufferStrategy(3); // in case it returns BufferStrategy. 
    bs = this.getBufferStrategy(); // otherwise 
} 

Answer 4

owww我很愚蠢的我忘了回应该是这样

private void render(){ 
    BufferStrategy bs = this.getBufferStrategy(); 
    if(bs == null){ 
     this.createBufferStrategy(3); 
     return; 
    } 

    Graphics g = bs.getDrawGraphics(); 

    g.dispose(); 
    bs.show(); 
}