获取字符串中不相同的字符重新组成字符串!!

package test;
import java.awt.*;
import java.awt.event.*;import javax.swing.*;
public class TestString implements ActionListener {
private static String s1;
private static String s2;
// private static StringBuffer s3=null;
JLabel label1,label2;
JTextField text1,text2;
JButton jb;
public TestString(){
label1=new JLabel("please insert into");
label2=new JLabel("Get The Result:");
text1=new JTextField(10);
text2=new JTextField(10);
jb=new JButton("Take It");
jb.addActionListener(this);
JFrame f=new JFrame("Only one Test");
Container contentPane=f.getContentPane();
contentPane.setLayout(new FlowLayout());
f.add(label1);
f.add(text1);
f.add(label2);
f.add(text2);
f.add(jb);
f.pack();
f.show();
//f.setSize(400, 200);
//f.setVisible(true);
f.addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent e){
System.exit(0);
}
});
}
public String setString(){
return s1=text1.getText();
}
public String getString(){
char a[]=new char[s1.length()];
int s=s1.length();
for(int i=0;i<s;i++)
{
a[i]=s1.charAt(1);
s1=s1.substring(2);
}
for(int i=0;i<s;i++)
{
String str=null;
if(s2.indexOf(a[i])<0){
str=String.valueOf(a[i]).toString();
s2.concat(str);
}
}
return s2;
}
/**
 * @param args
 */
public static void main(String[] args) {
new TestString();
// TODO 自动生成方法存根 }
public void actionPerformed(ActionEvent e) {
if(e.getSource()==jb){
setString();
text2.setText(getString());
}
// TODO 自动生成方法存根

}}
有异常不知道是什么意思,高手解决:
Exception in thread "AWT-EventQueue-0" java.lang.StringIndexOutOfBoundsException: String index out of range: 1
at java.lang.String.charAt(Unknown Source)
at test.TestString.getString(TestString.java:46)
at test.TestString.actionPerformed(TestString.java:70)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(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.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(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)