From: Josh Cheek <josh.cheek@...>
Date: 2010-02-14T13:25:38+09:00
Subject: Re: Why no ++ and --?

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I thought it might be interesting to see how Java handles this, since it has
both primitives and wrappers.

Outputs
primative1 = 6 , primative2 = 5
immutable1 = 6, immutable2 = 5
mutable1 = 4, mutable2 = 4



public class IntWrapper {
  public static void main(String[] args) {
    // Java does not support references to primitive types, so primative2 =
primative1 creates a new int
    // with the same value as primative1. Then when we incrememnt
primative1, primative2's value does not change
    int primative1 = 5;
    int primative2 = primative1;
    primative1++;
    System.out.println( "primative1 = " + primative1 + " , primative2 = " +
primative2 );

    // because Integer is immutable, immutable1 and immutable2 end up
pointing to different objects
    // and they have different values. This contradicts the C / C++ model,
as well as the general object model
    Integer immutable1 = new Integer(5);
    Integer immutable2 = immutable1;
    immutable1++;
    System.out.println( "immutable1 = " + immutable1 + ", immutable2 = " +
immutable2 );

    // an example of how mutable objects behave, that shows the difference,
in this case,
    // the object is mutable, so mutable1 and mutable2 both point to the
same object
    // and when it is updated, they both reflect this change
    // using a method .increment() because java does not support operator
overloading.
    IntWrapper mutable1 = new IntWrapper(3);
    IntWrapper mutable2 = mutable1;
    mutable1.increment();
    System.out.println( "mutable1 = " + mutable1 + ", mutable2 = " +
mutable2 );
  }

  public int num;
  public IntWrapper( int num ) { this.num = num; }
  public void increment() { num++; }
  public String toString() { return Integer.toString(num); }
}


Ruby avoids the criticism of contradicting the C/C++ model, and general
object model because it's immutable classes don't implement self-modifying
methods like ++, every method returns a new object.

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