Re: .equals(o) and Set membership

From: hiwa (HGA03630_at_nifty.ne.jp)
Date: 12/05/03

  • Next message: hiwa: "Re: .equals(o) and Set membership" 
    Date: 4 Dec 2003 21:38:45 -0800

    Murat Tasan <tasan@eecs.cwru.edu> wrote in message news:<Pine.SOL.4.53.0312041520470.18529@homer>...
    > i have a class, in which i have override the Object.equals(Object o)
    > method... and then i try to make two equal objects (under the new
    > definition) and place them into a HashSet... which should only accept one
    > of them, as in the following code. the class holds two objects (a pair of
    > objects) and if another member of the class contains the same two objects
    > (in either place of the ordered pair), it is considered equal.
    >
    > Integer key1 = new Integer(1);
    > Integer key2 = new Integer(2);
    > HashSet x = new HashSet();
    > // demonstrate that the equals() method works...
    > System.out.println((new MyClass(key1, key2)).equals(new myClass(key2,
    > key1)));
    > System.out.println(x.add(new MyClass(key1, key2)));
    > System.out.println(x.add(new MyClass(key2, key1)));
    >
    >
    > if i'm correct in reading the docs about how Set classes work, the output
    > of this should be:
    >
    > true
    > true
    > false
    >
    > but instead i'm getting:
    >
    > true
    > true
    > true
    >
    > and indeed the Set x has two elements after this code.
    >
    > i thought the Set code checks for membership by applying the .equals()
    > method, which at runtime should bind to my overridden method, no?
    >
    > thanks for any help,
    >
    > murat

    My guess is: your equals() method is not equal to the Object#equals()
    method in its signature. I also made the error in my Java beginner
    days, numerous times may be!

  • Next message: hiwa: "Re: .equals(o) and Set membership"

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