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From: markspace <markspace@nospam.nospam>
Newsgroups: comp.lang.java.programmer
Subject: Re: hash map / collection choice
Date: Sun, 27 Apr 2014 16:37:56 -0700
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On 4/27/2014 12:58 PM, Philipp Kraus wrote:

> A set should be the correct structure, but I can not get the object
> itself of the map without iteration over all
> items. A HashMap needs a key, value pair, so I need also a key class


If you'd prefer a set, I'd just make one.  It isn't that much trouble to 
do so.  The implementation might be a little slow, but if it gives you 
trouble then you just have to optimize it more.  Most time code like 
this won't be the bottle-neck.

Not tested.  I've renamed your get method to "findById", and you'll need 
a proper hash/equals method, one that compares all fields in MyEdge, for 
this to work 100%.


package quicktest;

import java.util.AbstractSet;
import java.util.HashMap;
import java.util.Iterator;

public class MySet extends AbstractSet<MyEdge>
{
    private final HashMap<Integer,MyEdge> map = new HashMap<>();

    @Override
    public Iterator iterator()   {
       return map.values().iterator();
    }

    @Override
    public int size()   {
       return map.size();
    }

    @Override
    public boolean add( MyEdge edge ) { // edge @NotNull
       MyEdge temp = map.get( edge.getID() );
       map.put( edge.getID(), edge);
       return !edge.equals( temp );
    }

    public MyEdge findById( int id ) {
       return map.get(id);
    }
}

// Dummy for compilation
class MyEdge{
   public int getID() {return 0;}
}