indexof它所查出来的是你给的母字符中某一个字符的下标位置,
以下引用自java1.6api文档：
Returns the index within this string of the first occurrence of the specified
character. If a character with value ch occurs in the character
sequence represented by this String object, then the index (in
Unicode code units) of the first such occurrence is returned.
还是举个例子吧
这里用这个方法定义一个验证输入字符为数字的方法：
public void KeyTyped(KeyEvent e){
String key="-0123456789.*";
if(key.indexOf(e.getKeyChar())<0)//如果getKeyChar返回的字符是是数字，那么indexOf返回的必然是这个数字在字符串"-0123456789.*"的下标
//如果返回值小于0 ，则输入字符不是数字，然后调用consume（）销毁该输入即可
e.consume();//销毁输入的非法字符
}
