What methods should go into a java.util.Objects class in JDK 7? (original) (raw)

Jason Mehrens jason_mehrens at hotmail.com
Fri Oct 2 22:14:35 UTC 2009

I think a better name would be "defaultToString" since it is the default toString from Object. However, I haven't ever heard anyone else request easier access to the default toString before so I'm not convinced this should go into Objects.

-Joe

One use case is implementing toString for identity maps and collections. The current IdentityHashMap is immune to poison objects except for its toString implementation. http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6579224

Another point of confusion is that the toString does not match what is going on in equals. Take the following code:

public static void main(String[] args) { Map<Integer, Integer> dis = new IdentityHashMap<Integer, Integer>(one()); Map<Integer, Integer> dat = new IdentityHashMap<Integer, Integer>(one());

System.out.println(dis.equals(dat));
System.out.println(dis.toString().equals(dat.toString()));

}

private static Map<Integer, Integer> one() { Integer kv = new Integer(256); return Collections.singletonMap(kv, kv); }

It prints false and then true. If defaultToString was used on the key/value pairs it would print false and then false making it clear why the two maps are not equal. Something to consider if a new reference map or identity map is added to the JDK (jsr166/extra166y).

Jason

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