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Another bizarre consequence of this philosophy becomes evident when we consider equality. Java has a built-in equality operator ==. However, if we write

Complex u = Complex(2,3);
Complex v = Complex(2,3);
System.out.println(u==v);  // Standard way to print.
we'll see the answer false. Surely this violates the principle of least astonishment, a principle which, according to [Plum], should be obeyed by language designers, and which is broken
... when a ``natural'' or ``abbreviated'' language construction leads the user to induce a model of underlying action different from what is actually performed by the machine.

That == can indeed mislead is also pointed out by Lemay and Perkins [Lemay and Perkins]. Java has a built-in object type String for storing sequences of characters. If you use == to compare two strings:

String a = "a string";
String b = "a string";
System.out.println( a==b );
you get the answer false, even if they contain the same characters. To circumvent this, it is suggested that the method equals, should be defined especially with the String type:
System.out.println( a.equals(b) );

Jocelyn Ireson-Paine
Mon Jan 12 14:15:07 GMT 1998