问题：我正在尝试添加使用Java内置图形方法的多个方法。绘制到屏幕的方法使用if语句。
我尝试过的方法：使用方法名称并更改（图形g）中的字符。此外，我试图将我遇到问题的方法放入paint方法块中。
使用的变量：
以下代码打印我的姓名首字母，删除文本字段并绘制图表的x轴和y轴：
public void paint(Graphics g) {
g.drawString("BWD", 450, 490); // Puts my signature in the bottom corner
inputField.setText("");
inputText = ("");
g.drawLine(50, 450, 460, 450);//Paints x-axis
g.drawLine(50, 450, 50, 100);//Paints the y-axis
}
以下代码的方法名称为paint。我试图改变它，但它仍然会返回问题。单击提交按钮时，我希望以下代码绘制到屏幕上：
public void paint (Graphics g)
{
for(int j=0, x=50, y = 100; j< wordLengths.length;j++)
{
if (wordLengths[j] == 1)
{
y = y+15;
g.drawString(wordLengths[j]+ " word of length "+ (j+1), x, y);
}
g.drawString("There are: ", 50, 90);
if (wordLengths[j] > 1)
{
y = y+15;
g.drawString(wordLengths[j]+ " words of length "+ (j+1), x, y);
}
}
}
理想的代码是：
public void paint(Graphics g) {
g.drawString("BWD", 450, 490); // Puts my signature in the bottom corner
inputField.setText("");
inputText = ("");
g.drawLine(50, 450, 460, 450);//Paints x-axis
g.drawLine(50, 450, 50, 100);//Paints the y-axis
for(int j=0, x=50, y = 100; j< wordLengths.length;j++)
{
if (wordLengths[j] == 1)
{
y = y+15;
g.drawString(wordLengths[j]+ " word of length "+ (j+1), x, y);
}
g.drawString("There are: ", 50, 90);
if (wordLengths[j] > 1)
{
y = y+15;
g.drawString(wordLengths[j]+ " words of length "+ (j+1), x, y);
}
}
}
如果需要任何其他信息，请不要犹豫，添加评论，我会非常快速地加入评论！
提前致谢！
Exception in thread "AWT-EventQueue-1" java.lang.NullPointerException
at java_assignment.JavaAppletMain.paint(JavaAppletMain.java:114)
at sun.awt.RepaintArea.paintComponent(RepaintArea.java:264)
at sun.lwawt.LWRepaintArea.paintComponent(LWRepaintArea.java:54)
at sun.awt.RepaintArea.paint(RepaintArea.java:240)
at sun.lwawt.LWComponentPeer.handleJavaPaintEvent(LWComponentPeer.java:1267)
at sun.lwawt.LWComponentPeer.handleEvent(LWComponentPeer.java:1150)
at java.awt.Component.dispatchEventImpl(Component.java:4937)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:735)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:694)
at java.awt.EventQueue$3.run(EventQueue.java:692)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:708)
at java.awt.EventQueue$4.run(EventQueue.java:706)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:705)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91))
Thread [AWT-EventQueue-1] (Suspended (breakpoint at line 112 in JavaAppletMain))
JavaAppletMain.paint(Graphics) line: 112
LWRepaintArea(RepaintArea).paintComponent(Component, Graphics) line: 264
LWRepaintArea.paintComponent(Component, Graphics) line: 54
LWRepaintArea(RepaintArea).paint(Object, boolean) line: 240
LWPanelPeer(LWComponentPeer<T,D>).handleJavaPaintEvent() line: 1267
LWPanelPeer(LWComponentPeer<T,D>).handleEvent(AWTEvent) line: 1150
JavaAppletMain(Component).dispatchEventImpl(AWTEvent) line: 4937
JavaAppletMain(Container).dispatchEventImpl(AWTEvent) line: 2287
JavaAppletMain(Component).dispatchEvent(AWTEvent) line: 4687
EventQueue.dispatchEventImpl(AWTEvent, Object) line: 735
EventQueue.access$200(EventQueue, AWTEvent, Object) line: 103
EventQueue$3.run() line: 694
EventQueue$3.run() line: 692
AccessController.doPrivileged(PrivilegedAction<T>, AccessControlContext) line: not available [native method]
ProtectionDomain$1.doIntersectionPrivilege(PrivilegedAction<T>, AccessControlContext, AccessControlContext) line: 76
ProtectionDomain$1.doIntersectionPrivilege(PrivilegedAction<T>, AccessControlContext) line: 87
EventQueue$4.run() line: 708
EventQueue$4.run() line: 706
AccessController.doPrivileged(PrivilegedAction<T>, AccessControlContext) line: not available [native method]
ProtectionDomain$1.doIntersectionPrivilege(PrivilegedAction<T>, AccessControlContext, AccessControlContext) line: 76
EventQueue.dispatchEvent(AWTEvent) line: 705
EventDispatchThread.pumpOneEventForFilters(int) line: 242
EventDispatchThread.pumpEventsForFilter(int, Conditional, EventFilter) line: 161
EventDispatchThread.pumpEventsForHierarchy(int, Conditional, Component) line: 150
EventDispatchThread.pumpEvents(int, Conditional) line: 146
EventDispatchThread.pumpEvents(Conditional) line: 138
EventDispatchThread.run() line: 91
答案 0 :(得分：3)
您只是在wordLenghts中初始化数组actionPerformed。但是在程序启动时调用paint，并且从未调用actionPerformed来初始化数组。这就是为什么你得到NPE。
您应该在构造函数或init方法中初始化它。
private int[] wordLength;
@Overrde
public void init() {
wordLength = new int[0];
}