[英]Java JOptionPane Dialog NullPointerException
下面的代码运行完美,但是如果在对话框上单击“ x”或“取消”,则会引发NullPointerException
。 我正在尝试调用方法TestMessage
并返回到同一对话框。
import javax.swing.JOptionPane;
public class Alpha {
public void TestMessage() {
Object [] tM1={"Option 1","Option 2","Option 3"};
String mA2 = (String) JOptionPane.showInputDialog(null,"This is a test Message",null, JOptionPane.QUESTION_MESSAGE, null,tM1,tM1[0]);
if (mA2.equals("Option 1")) {JOptionPane.showMessageDialog(null,"You chose Option 1");}
if (mA2.equals("Option 2")) {JOptionPane.showMessageDialog(null,"You chose Option 2");}
if (mA2.equals("Option 3")) {JOptionPane.showMessageDialog(null,"You chose Option 3");}
}
public static void main (String [] args) {
Alpha A1=new Alpha();
A1.TestMessage();
}
}
错误信息:
java.lang.NullPointerException
at Alpha.TestMessage(Alpha.java:11)
at Alpha.main(Alpha.java:20)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at edu.rice.cs.drjava.model.compiler.JavacCompiler.runCommand(JavacCompiler.java:272)
如果您按“取消”或“ X”,则showInputDialog
返回null
,以便检查if (mA2.equals("Option 1")
访问null
指针。只需在之前检查mA2 != null
。
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