Passing a String by Reference in Java?

Question

I am used to doing the following in C:

void main() {
    String zText = "";
    fillString(zText);
    printf(zText);
}

void fillString(String zText) {
    zText += "foo";
}

And the output is:

foo

However, in Java, this does not seem to work. I assume because the String object is copied instead of passed by referenced. I thought Strings were objects, which are always passed by reference.

What is going on here?

Answer 1

You have three options:

1. Use a StringBuilder:

   StringBuilder zText = new StringBuilder ();
   void fillString(StringBuilder zText) { zText.append ("foo"); }
   

2. Create a container class and pass an instance of the container to your method:

   public class Container { public String data; }
   void fillString(Container c) { c.data += "foo"; }
   

3. Create an array:

   new String[] zText = new String[1];
   zText[0] = "";
   
   void fillString(String[] zText) { zText[0] += "foo"; }
   

From a performance point of view, the StringBuilder is usually the best option.