Wrapper class in java is it a class with primitive data type as member?

Question

I want to know how Integer class works: Consider

Integer number=2;

Does this mean, "Integer" class has a constructor like mentioned below and it stores the int value in it? Please explain.

class Integer
{
    int a;

    public Integer (int a)
    {
        this.a=a;
    }
}

Answer 1

Pretty close. Check out the source code for Integer (apparently from Harmony so the Sun/Oracle JVM may be a bit different). Autoboxing conversions (when you assign a primitive to a wrapper class) use the equivalent of valueOf, which caches "common" integers and creates new ones for the rest.

Answer 2

javac generates code to call Integer.valueOf(int) which may or may not construct a new Integer or just reuse an existing one. In the JLS this is covered by "boxing conversions".