最简单两行代码的有关问题，求救求救！关于replaceAll

最简单两行代码的问题，求救求救！！！关于replaceAll
public   class   T
{

public   static   void   main(String[]   args)
{
String   st= "sssss ";
st.replaceAll( "s ", "$ ");
}

}


Exception   in   thread   "main "   java.lang.StringIndexOutOfBoundsException:   String   index   out   of   range:   1
at   java.lang.String.charAt(Unknown   Source)
at   java.util.regex.Matcher.appendReplacement(Unknown   Source)
at   java.util.regex.Matcher.replaceAll(Unknown   Source)
at   java.lang.String.replaceAll(Unknown   Source)
at   T.main(T.java:7)


[解决办法]
st.replaceAll( "s ", "\\$ ");
[解决办法]
改成
st.replaceAll( "s ", "\\$ ");

[解决办法]
public class T
{

public static void main(String[] args)
{
String st= "sssss ";
System.out.print(st.replaceAll( "s ", "\\$ "));
}

}