【3】Remove the duplicate characters in a string

Question: Design an algorithm and write code to remove the duplicate characters in a string without using any additional buffer. NOTE: One or two additional
variables are fine An extra copy of the array is not.

package CareerCup;

public class RemoveDuplicateChar
{
public RemoveDuplicateChar(){}

public String removeDuplicate(String str)
{
if(str.length()<=1 || str==null) return str;

String strRemove = "";
char ch = str.charAt(0);
strRemove += str.charAt(0);
for(int i=1;i<str.length();i++)
{
if(str.charAt(i)!=ch)
{
strRemove += str.charAt(i);
ch = str.charAt(i);
}
}
return strRemove;
}

public static void main(String[] args)
{
String str = "seeyeeeey";
RemoveDuplicateChar rdc = new RemoveDuplicateChar();
String strRemove = rdc.removeDuplicate(str);
System.out.println("The orignal string:"+str);
System.out.println("The removed string:"+strRemove);
}
}