java中的包装类是一个原始数据类型为成员的类吗？

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" .

Answer 3

这意味着自动拳击到位。

Answer 4

You can always find the latest OpenJDK Integer class here :

The relevant field is (from line 645):

/**
 * The value of the {@code Integer}.
 *
 * @serial
 */
private final int value;