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Suppose I have an object ClassRoom, in the ClassRoom there are many Student objects (50 objects) with more than 20 properties, many Teacher objects (10 objects) with more then 20. ClassRoom also has some other properties like classNo, seatCapacity, etc.

Is it good to pass a object of ClassRoom object as an argument to a method. Suppose I need only 3-4 properties of ClassRoom and 1-2 properties of each Students. If it is bad, what is the cost of passing a heavy object.

Mark Rotteveel
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ParagFlume
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    There are no costs associated with the weight of an object. Object is never the value of a variable (or method argument), it is the _reference_ to the object. – Marko Topolnik Jul 30 '15 at 08:30
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    Passing object is just a memory pointing that does not cost. – Naveen Ramawat Jul 30 '15 at 08:34
  • [Here](http://stackoverflow.com/a/40523/5132172) is a more detailed / comprehensible answer from SO. It explains how arguments are passed in methods: (Not as trivial as you may think) –  Jul 30 '15 at 08:36

4 Answers4

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In Java you are passing a reference to object. And there's no cost difference when you pass a String instance or a complex class instance, like your ClassRoom class.

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Forget about the memory, that's negligible. The answer is depends . Just pass based on your business logic instead of thinking about memory and yes JVM deals it better.

If you don't want the other method modifying the fields of your object, then don't pass the object. Just pass the required properties. If not, then its better to pass the object reference and use the values from it instead of adding those many parameters in method signature.

Suresh Atta
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There is no difference.The object is in a heap memory, and you're just using the reference to the object in stack memory.

Sean Zhang
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I think that the JVM manages it for you, so you won't feel any performance problems, plus you're not passing the whole object by value, but you pass the object reference by value (kind of copy of a pointer). Hope it helps.

Felix Av
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