Reference parameters? 2

[timmay3141]

I'm learning java with a background in C++. I was writing a method, but was surprised to discover that I couldn't use a reference parameter using C++ syntax. How do you use them? Surely there must be some way. Also, C++ pointer syntax doesn't work. Is it even possible to declare a pointer in java?

 

[dbleyl]

Almost everything in java is passed by reference. You don't do anything special. No pointers.

 

[EBGreen]

In Java all parameters are passed by value. If the parameter is a primitive data type, then the data value of the actual parameter is passed. If the parameter is a reference to an object, then the reference value is passed.

 

[dbleyl]

Whoops - I stand corrected.

http://www-106.ibm.com/developerworks/java/library/j-passbyval/

It is confusing. Pass by reference is not the same as passing the value of a reference.

SomeObject o1 = someObject.instance();
o1.color = Color.GREEN;
change(o1);
change2(o1);
//o1 is still RED.
...
private void change(SomeObject o) {
o.color = Color.RED;
//now o1 color is read.
}

private void change2(SomeObject o) {
o = null;
//doesn't change o1, still RED.
}

 

[EBGreen]

Here are a couple of good explanations as well:

http://java.sun.com/developer/JDCTechTips/2001/tt1009.html

http://javadude.com/articles/passbyvalue.htm

 

[timmay3141]

Thank you, that was very helpful. I'm not sure how I will adjust to life without explicit pointers and references, but I'll find a way .

 

[EBGreen]

There are some workarounds. What specifically were you trying to do?

 

[sedj]

It can be quite simple, just change the way you think ...

public class Test {
   public String setS1(String s) {
      s = s +" hello";
      return s;
   }

   public void doSomething() {
     String s = "abcdef";
     System.err.println(s);
     s = setS1(s);
     System.err.println(s);
   }
}