无法在另一个班级中创建打印Methord并将其称为主班级

|| 我在名为tree的类中创建了此方法：

public void printTree(Graphics g, int x, int y) {
MediaTracker mt = new MediaTracker(this);
tree = getImage(getCodeBase(), \"tree.png\");
mt.addImage(tree, 0);
g.drawImage(tree, x, y, this);

我尝试在主要的paint方法中使用它：

Tree tree = new Tree();
    tree.printTree(g, 60, 50);

我没有收到任何错误，但是当我运行应用程序时出现了以下错误：

    Exception in thread \"AWT-EventQueue-1\" java.lang.NullPointerException
at java.applet.Applet.getCodeBase(Unknown Source)
at Tree.printTree(Tree.java:12)
at Main.paint(Main.java:146)
at Main.update(Main.java:187)
at sun.awt.RepaintArea.updateComponent(Unknown Source)
at sun.awt.RepaintArea.paint(Unknown Source)
at sun.awt.windows.WComponentPeer.handleEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$000(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$2.run(Unknown Source)
at java.awt.EventQueue$2.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(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)

如果有人可以帮助我，我将非常高兴。

已邀请:

3 个回复

赐黄

Applet在AppletContext中运行是否由appletviewer提供或浏览器页面。如果您运行从主要方法或加载小程序小程序进入应用程序没有AppletContext和getCodeBase 将返回null。在这种情况下，您可以使用备用/其他图像加载方法。参考使用另一种方法将图片导入小程序。