java - 为什么我不断收到 Java.Lang.NullPointerException

Question

我在此代码上不断收到 Java.Lang.NullPointerException:

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

    Graphics g = bs.getDrawGraphics();

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

有人能告诉我我做错了什么吗？

Answer 1

即使您调用 this.createBufferStrategy(3);，您的 bs 变量仍然未分配。

创建后需要读回它:

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

最好添加一个检查，以确保在调用 createBufferStrategy 之后返回一个非 null:

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