ITEC 120 2012fall dbraffitt ibarland

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lect08b
Memory diagrams, continued
aliasing and mutation; pass-by-value

What `equals` means: If you don't do anything to say otherwise, your own classes have a equals (inherited from java.lang.Object) which just does the same thing == does (?!):

// Inside class java.lang.Object, deep in the bowels of Java: public boolean equals(Object that) { return this == that; }

If you want equals to do something smarter, you have to write it yourself (“overriding the version inherited from Object”). That's what class String does, which is why equals works for Strings.

We will draw pictures for the following:

  int n = 7;
  int k = n;
  
  Song s1 = new Song(...);
  Song s2 = s1;
  Song s3 = new Song(...);

  assigning( n, s2 );

  static void assigning( int z, Song lalala ) {
    lalala.artist = "Justin Bieber";  // I am *not* assigning to a local variable!  Others referring to object can see changes.
    z = z+1;                          // assigning to my local variable -- nobody else can see changes.
    lalala = new Song(...)            // assigning to my local variable -- nobody else can see changes.
    }

home—info—lects—labs—exams—hws
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Object120 + its docs—java.lang docs—java.util docs

©2012, Ian Barland, Radford University Last modified 2012.Oct.17 (Wed)

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