Try this code,you may got the expected answer,
String str="a b c";
boolean a1 = true ;
StringBuilder strbu = new StringBuilder();
for(int i=0 ; i<str.length();i++)
{
Character b = str.charAt(i);
if(b.equals(' ') && a1 == true )
{
a1 = false;
strbu = strbu.append("AA");
}
else
{
strbu = strbu.append(b);
}
}
Log.e("str","string:"+strbu.toString());
solved android change first blank to “AA”