Are Java function parameters always passed-by-value for arrays?

Question

Possible Duplicate:
Is Java “pass-by-reference”?

if we have big byte[] array (like 40Mb) and we want to send it in method

method(array);

will the array be copied? So memory will increase by another 40Mb in Java env => 80Mb, right?

If yes, how can we destroy the 'first' array after calling the method?

See also http://stackoverflow.com/questions/15871825/why-is-an-arraylist-parameter-modified-but-not-a-string-parameter — Raedwald, Apr 30 '14 at 07:39

score 7 · Accepted Answer · answered Dec 14 '12 at 10:57

No, the array will not be copied.

In Java, everything is always passed by value.

Variables of non-primitive types are references to objects. An array is an object, and a variable of an array type is a reference to that array object.

When you call a method that takes a non-primitive type parameter, the reference is passed by value - that means, the reference itself is copied, but not the object it refers to.

score 1 · Answer 2 · answered Dec 14 '12 at 10:55

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No new Object will be created, Just a reference will be copied to function parameter.

answered Dec 14 '12 at 10:55

Subhrajyoti Majumder

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score 1 · Answer 3 · answered Dec 14 '12 at 10:56

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The variable array is actually just a reference to the array object. When you pass array to a function you are just copying the reference not the actual array the the reference refers.

answered Dec 14 '12 at 10:56

codaddict

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score 1 · Answer 4 · answered Dec 14 '12 at 10:57

Java is always pass by value. The value being passed is the value of the variable in the case of a primitive type and the value of the reference held by a variable in the case of an Object.

In this case, an array is an Object and what is passed by value is the reference to that Object. So no, the array will not be copied.

hqt · Answer 5 · 2012-12-14T11:04:14.643

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No, the array will not be copied. In fact, because:

In Java, everything is always passed by value.
Array itself is a object.

So, the result is array' will be copy for method, but the thing it contains: bytes elements DOES NOT copy. so, everything you change for array in the method will affect the original array.

So, memory will not double as you see :)

edited Dec 14 '12 at 11:04

answered Dec 14 '12 at 11:01

hqt

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Just curious, on point 2, does "Array" extend "Object"? :-) – Ravindranath Akila Dec 05 '13 at 07:40
every object in java extends Object ;) – hqt Dec 05 '13 at 12:51
An array of primitives is an Object? – Ravindranath Akila Dec 06 '13 at 03:29
Indeed! http://stackoverflow.com/questions/12806739/is-an-array-a-primitive-type-or-an-object-or-something-else-entirely – Ravindranath Akila Dec 06 '13 at 03:30

Are Java function parameters always passed-by-value for arrays?

5 Answers5