CODEWITHSUNDEEP
javadictionary
marxin
marxin

Reputation: 3922

Is it possible to modify item in Map without removing?

I have ConcurrentMap<Integer, MyObj> in my program. Can I modify MyObj if I know a key? Without deleting and putting a new MyObj?

Upvotes: 0

Views: 134

Answers (3)

Fermin Silva
Fermin Silva

Reputation: 3377

Not only that, but if you keep the original reference to the object, you can still modify it.

MyObject o = new MyObject();
myMap.put("key", o);

o.setName("foo");
myMap.get("key").getName(); //will return "foo"
myMap.get("key").setName("bar");
myMap.get("key").getName(); //will return "bar"

o = null; //this applies only for your local reference, not for the map
myMap.get("key").getName(); //will STILL return "bar"

Upvotes: 3

Craig Wohlfeil
Craig Wohlfeil

Reputation: 647

Yes you can. The map simply holds a reference to the object. The object can change without having to update the map.

Map<Integer, MyObj> myMap = new ConcurrentMap<Integer, MyObj>();
myMap.put(1, new MyObj());
MyObj obj = myMap.get(1);
obj.setFoo("Foo");

Upvotes: 0

Matt Ball
Matt Ball

Reputation: 359816

It depends on your definition of "modify." If you want to mutate something internal to MyObj, and that object is mutable, you certainly can do this.

ConcurrentMap<Integer, MyObj> map = /* snip */;
map.get(someKey).callMutatorMethod();

If you want to replace the object with an entirely new instance, you can just call Map#put(), which will overwrite the existing mapped value, if such a value exists.

Upvotes: 4

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