Where are int values and Integer Objects created?

Question

When we initialize some integer values like

int a = 10; 

or

Integer b = new Integer(20);
Integer b = 30;

where are those objects created in memory?

Is there any concept like Integer-Pool like we have String-Pool for String?

Answer 1

Most JVMs (even 64-bit ones) use 32-bit references. (Newer JVMs uses 32-bit references for heaps up to almost 32 GB) The reference is on the stack or in a CPU register and is not usually counted. The Integer is allocated on the heap.

Integer i = new Integer(1); // creates a new object every time.
Integer j = 1; // use a cached value.

Integer a; will allocate memory in stack to hold the reference value and initialized with null

new creates instance in heap memory

Answer 2

Objects created with new keyword are stored on heap.

Variables (references to those objects) and primitive types like int are stored on program's stack.

Integer is not a special class in Java. You can use arithmetic operators with it, it's immutable and you can even use == for equality testing (in the range of -128 to 127 since those values are already cached).

Is there any concept like Integer-Pool like we have String-Pool for String?

Open the code of java.lang.Integer and look at the valueOf method. It's obvious that they indeed use an Integer pool.

public static Integer valueOf(int i) {
    assert IntegerCache.high >= 127;
    if (i >= IntegerCache.low && i <= IntegerCache.high)
        return IntegerCache.cache[i + (-IntegerCache.low)];
    return new Integer(i);
}

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