Java Trie节点布尔值与布尔值

Question

I'm creating trie node class, which contains field with logical type and I don't know what will be better use boolean or Boolean.

I know that one instance of Boolean takes 16 Bytes and 4 bytes takes it reference in 32-bit VM. But Boolean have constants Boolean.TRUE and Boolean.FALSE, what can be used for space optimization. So application wiil takes 4*N+32 Bytes, where N is number of nodes, yes?

As far, as I know boolean value takes 4 bytes (in array it optimize to 1 byte per element) in 32-bit VM too)

However I can use code like this

boolean EOW = Boolean.TRUE;

but how many space it will take and how many time wiil take autboxing/inboxing?

So what will be better to use to optimize space usage and time? And could you answer me how many space it tales on 64-bit VM?

Answer 1

Just use the primitive type boolean with true and false . Primitive types take less memory, work with better performance and are null-safe.

Answer 2

Instead of this:

boolean EOW = Boolean.TRUE;

Just write this:

boolean EOW = true;

There is no reason to use Boolean.TRUE , it will be auto-unboxed to the primitive value true anyway, it's more efficient and less verbose to use the value true directly.

Only use wrapper classes such as Boolean when you have a good reason to do so - otherwise, use primitive types such as boolean . One reason to use a wrapper is when you need to store values in a collection (such as an ArrayList ) - collection classes can only hold objects and not primitive values, so you'll have to use the wrapper class in that case.

Using Boolean objects is never more efficient than using boolean primitive values.

Note that primitive values are just values , not objects. If you use the value true ten times in your code, there will not be ten duplicate objects in memory.

Answer 3

I expect the exact code, that you pasted, to be optimized to boolean EOW = true; , so it shouldn't be unboxed at all, but if there's no such an optimization, then you'll haven't any memory affected, because you use the static field, which will be initialized only once. Nevertheless, you still will lose one operation on imlicit running method booleanValue() , which will just return stored value. Actually, I don't have any idea, why you would want to have such an expression.