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package myintergertest; /** * * @author Engineering */ public class Main { /** * @param args the command line arguments */ public static void main(String[] args) { //this one does not increment Integer n = new Integer(0); System.out.println("n=" + n); Increment(n); System.out.println("n=" + n); Increment(n); System.out.println("n=" + n); Increment(n); System.out.println("n=" + n); Increment(n); //this one will increment MyIntegerObj myInt = new MyIntegerObj(1); Increment(myInt); System.out.println("myint = " + myInt.get()); Increment(myInt); System.out.println("myint = " + myInt.get()); Increment(myInt); System.out.println("myint = " + myInt.get()); } public static void Increment(Integer n) { //NO. this doesn't work because a new reference is being assigned //and references are passed by value in java n++; } public static void Increment(MyIntegerObj n) { //this works because we're still operating on the same object //no new reference was assigned to n here. n.plusplus(); //I didn't know how to implement a ++ operator... } } The result for all of those is n=0. Integer n is an object and therefore passed by reference, so why isn't the increment reflected back in the caller method (main)? I expected output to be n=0 n=1 n=2 etc... UPDATE: Notice I updated the code example above. If I'm understanding correctly, Jon Skeet answered the question of why myInt would increment and why n does not. It is because n is getting a new reference assigned in the Increment method. But myInt does NOT get assigned a new reference since it's calling a member function. Does that sound like I understand correctly lol ?

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