Pass by reference? I think not!

Question

As I understand it, Java code automatically passes everything by reference. The code that I've written seems not to do this though.
     String benefitID = new String();
     String allBenID = new String();
          try
               benefitInfoDAO.selectIDs(awardCode, i, benefitID, allBenID);
          catch (CMSException e)
               throw e;
          }The strings benefitId and allBenID are assigned values in the selectIDs method. However, when execution returns to the calling method, their values are "". What's going on?

Answer 1

You forget that Strings are immutable objects, and when you pass the String into that other method, you are actually passing THAT String object into that method, here is an example.
class Bob()
Bob()
String myString = "Hello";
doSomething(myString);
System.out.println(myString); //Still prints out "Hello"
public void doSomething(String inString)
System.out.println(inString); //Prints out "Hello"
inString = "Bye!";
System.out.println(inString); //Prints out "Bye!"
Why is this? This is because Java passes everything as pointers, and not as C++ "References". Strings are also special, because they are immutable objects, there is no real way to manipulate a String object's memory once it's created. You can however do this to achieve the result you were looking for:
class Bob()
Bob()
StringBuffer myString = new StringBuffer("Hello");
doSomething(myString);
System.out.println(myString.toString()); //Now it prints out "Bye!"
public void doSomething(StringBuffer inString) //inString is a NEW pointer, you can change where it's pointing, but it will not change where myString in pointing!
System.out.println(inString.toString()); //Prints out "Hello"
inString.setLength(0);
inString.append("Bye!");
System.out.println(inString.toString()); //Prints out "Bye!"
}