java Slidepuzzle，切换图标
我们正在使用Eclipse在java中制作一个slidepuzzle。我们在按钮上加了Icon。现在我们想用所谓的“空按钮”的图标来切换我们点击的按钮的Icon
int location =(new Integer(e.getActionCommand())).intValue(); //The buttons are in an Array: "Pieces[]", Location: index
if (Bounds(location,InvisibleButton)) {
//The method Bounds, is one we made to see if the two pieces are next to eachother,
Icon temp; //Temporar ButtonIcon
temp=Knop[location].getIcon();
Pieces[location].setIcon(Piece[InvisibleButton].getIcon());
Pieces[InvisibleButton].setIcon(temp);
InvisibleButton = location;
}
为什么图标不切换位置
错误：
只有当我们点击空工件旁边的工件时，它才会给出一个错误，我们可以点击所有其他工件。代码是有效的，但当我们想要切换图像时，它就会中断。 以下是错误代码：
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at Mozaiq.Schuifpuzzelpaneel.actionPerformed(Schuifpuzzelpaneel.java:93)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2028)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2351)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.java:6382)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3275)
at java.awt.Component.processEvent(Component.java:6147)
at java.awt.Container.processEvent(Container.java:2083)
at java.awt.Component.dispatchEventImpl(Component.java:4744)
at java.awt.Container.dispatchEventImpl(Container.java:2141)
at java.awt.Component.dispatchEvent(Component.java:4572)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4619)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4280)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4210)
at java.awt.Container.dispatchEventImpl(Container.java:2127)
at java.awt.Window.dispatchEventImpl(Window.java:2489)
at java.awt.Component.dispatchEvent(Component.java:4572)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:710)
at java.awt.EventQueue.access$400(EventQueue.java:82)
at java.awt.EventQueue$2.run(EventQueue.java:669)
at java.awt.EventQueue$2.run(EventQueue.java:667)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
at java.awt.EventQueue$3.run(EventQueue.java:683)
at java.awt.EventQueue$3.run(EventQueue.java:681)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:680)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
# 1 楼答案
快速猜测一下：调用repaint（）方法
可能是这样的：
在你工作的最后
# 2 楼答案
所以问题似乎是
Knop[location]不包含对工件对象的引用。也许这是一个更好的方法：错误