when doing OOP cannot output a String in if else

when i was doing a if else statement on the get methods I cannot output a check String in int length and want to set Gh to "AAAAA" the code is

public String getGh(){
        int length = Gh.length();
        if (length == 0){
            Gh="AAAAA";
        }else{
            Gh= null;
        }
    return this.Gh;
}
public String ShowGh() {
    return ("Title: "+this.Gh);

output is nothink, please help