How to make List.contains(Object) work when you write your own .equals func

Question

I have a list of objcts of a class defined by me. I want to use the List.contains(String name) function to tell me if it contains an object of that name. I have overriden the .equals function as shown in [1]. I then use the code at [2] to to test it, with a bit of debugger output as shown in [3]. It is not working, my overriden method is not getting called by List.contains(String name).
Can anyone tell me how to get this to work?
[1]     @Override public boolean equals(Object esId) {
        if(esId.getClass().isAssignableFrom(String.class)) {
            System.out.println("object name " + this.eslimId + " compare to " + esId + " = " + this.eslimId.equals(esId));
            return this.eslimId.equals(esId);
        } else {
            System.out.println("wrong class");
            return super.equals(esId);
    }[2] graphics.getProcedures() returns private List<ProcedureGraphicSet> procedures;
System.out.println( " graphics.getProcedures().get(0).equals(\"ESLIM_009\")= " + graphics.getProcedures().get(0).equals("ESLIM_009"));
System.out.println( " graphics.getProcedures().contains(\"ESLIM_009\")= " + graphics.getProcedures().contains("ESLIM_009"));[3]
object name ESLIM_009 compare to ESLIM_009 = true
graphics.getProcedures().get(0).equals("ESLIM_009")= true
graphics.getProcedures().contains("ESLIM_009")= false

Answer 1

This is a gross violation of the contract for the equals method, and you are basically getting bitten by that. The equals method must be symmetric, meaning this must hold for all objects A and B:
A.equals(B) == B.equals(A)This does not hold for your equals method because for any string A and custom object B:
A.equals(B) == falseAnd, apparently, the List.contains() method is choosing to compare objects that way.
You must iterate through the list and check the names yourself, or use some sort of functional package which provides a List.contains() type method which takes a Predicate object of some sort.
Edited by: jtahlborn on Feb 11, 2008 11:03 AM
Edited by: jtahlborn on Feb 11, 2008 11:03 AM