StringIndexOutOfBoundsException

"a/a/a/a/".replaceAll("/","\\")

Why does this generate:

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 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)

[641 byte] By [Nethera] at [2007-11-27 8:40:47]