我无法确定为什么我的代码会得到nullPointer异常.我正在尝试使用Java和Clojure的组合编写一个swing应用程序.我有一个Clojure函数,该函数在我的JPanel子类中调用一个函数,而且我遇到了很多让我发疯的异常.

我已尽可能简化了我的代码,但仍然遇到这些错误.

(defn draw-state
  "Draws the current state."
  [state display]
  (do-swing (.drawBlocks display)))

这是整个JPanel子类,尽管我认为唯一相关的部分是drawBlocks函数(该函数最终将替换blocks数组)：

public class TDisplay extends JPanel {


private Block[] blocks = new Block[1]; 

/**
 * Create the panel.
 */
public TDisplay() {
    setBorder(new BevelBorder(BevelBorder.LOWERED, null, null, null, null));
    setBackground(Color.WHITE);
    setLayout(new FlowLayout(FlowLayout.CENTER, 5, 5));
    blocks[0] = new Block(3, 4, 0);
}

public void paintComponent(Graphics g) {
    super.paintComponent(g);
    for (Block b : blocks) {
        if (b == null) continue;

        switch (b.colour) {
        case 0:
            g.setColor(Color.WHITE);
            break;
        case 1:
            g.setColor(Color.BLACK);
            break;
        }                               
        g.fillRect(b.x * Block.SIZE, b.y * Block.SIZE, Block.SIZE, Block.SIZE);
    }                
}

public void drawBlocks() {
    System.out.println("Hello world");
}

}

和堆栈跟踪：

Exception in thread "AWT-EventQueue-0" java.lang.RuntimeException: java.lang.NullPointerException
at clojure.lang.AFn.run(AFn.java:28)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
Caused by: java.lang.NullPointerException
at clojure.lang.Reflector.invokeNoArgInstanceMember(Reflector.java:263)
at core$draw_state$fn__401.invoke(core.clj:43)
at clojure.lang.AFn.run(AFn.java:24)
... 8 more

我觉得我确实缺少一些明显的东西,感谢您的帮助.

谢谢！

解决方法:

调用draw-state的代码怎么样？是否有可能传入null进行显示？