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javaandroidmemory-management
Laurent
Laurent

Reputation: 1739

Objects memory management in Java on Android

If I have :

How the memory is managed ? all "linked" objects (B,C,D...) are instanciated and put in memory when the object A is instanciated ?

Upvotes: 0

Views: 66

Answers (2)

Dorian Gray
Dorian Gray

Reputation: 2981

The statement List<String> strings = new ArrayList<>(); only allocates heap space for the list itsself, the list only stores references to the object it contains, it doesn't contain the objects themselves.

Note that an ArrayList is using an array as it's internal structure (you might have guessed that), so the constructor is basically allocating an array of an initial size. For creating huge ArrayLists, you should pre-allocate space to be more efficient, e.g. List<String> strings = new ArrayList<>(2000); preallocates space for 2000 String references.

Upvotes: 0

GhostCat
GhostCat

Reputation: 140437

Each time you call new() the memory required for the corresponding object is taken from the heap.

As you most often start by creating an empty list - only the memory required for that thing is requested.

In other words: there is no way to create the "complete" structure in one shot. It makes no difference if you do:

List<List<String>> strings = new ArrayList<>();

or

List<Number> numbers = new ArrayList<>();

The amount of memory that is allocated on the heap is the same for both of these instructions! Because in both cases one new object is created (that ArrayList instance).

Upvotes: 1

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