getX()方法调用的时候报错NullPointerException，怎么办啊~

Question

本帖最后由 betterglobe 于 2009-12-29 23:28:42 编辑

Answer 1

界面布局代码在这里
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createSequentialGroup()
                        .addComponent(startLeft, javax.swing.GroupLayout.PREFERRED_SIZE, 90, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                        .addComponent(stopLeft, javax.swing.GroupLayout.PREFERRED_SIZE, 88, javax.swing.GroupLayout.PREFERRED_SIZE))
                    .addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createSequentialGroup()
                        .addComponent(startRight, javax.swing.GroupLayout.PREFERRED_SIZE, 63, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addGap(2, 2, 2)
                        .addComponent(stopRight)
                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                        .addComponent(clearAll, javax.swing.GroupLayout.DEFAULT_SIZE, 71, Short.MAX_VALUE))
                    .addComponent(jPanel2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                    .addComponent(jPanel2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(startLeft)
                    .addComponent(stopLeft)
                    .addComponent(startRight)
                    .addComponent(stopRight)
                    .addComponent(clearAll))
                .addContainerGap())
        );

Answer 2

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at DrawThread.<init>(DrawThread.java:21)
        at RandomLines.<init>(RandomLines.java:200)
        at RandomLines$6.run(RandomLines.java:192)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:235)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:603)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:286)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:201)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:191)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:186)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:178)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:139)

Answer 3

public class NullPointerException
extends RuntimeException
当应用程序试图在需要对象的地方使用 null 时，抛出该异常。这种情况包括： 调用 null 对象的实例方法。 
访问或修改 null 对象的字段。 
将 null 作为一个数组，获得其长度。 
将 null 作为一个数组，访问或修改其时间片。 
将 null 作为 Throwable 值抛出。 
应用程序应该抛出该类的实例，指示其他对 null 对象的非法使用。 
根据提示你的行数去看呗