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;
    }
}

No reason to guess what Integer class has. Take a look at the source code yourself kickjava.com/src/java/lang/Integer.java.htm — CoolBeans
– CoolBeans, Commented Feb 14, 2011 at 4:50
One exception would be Void which doesn't have a public constructor (or a value inside) — Peter Lawrey
– Peter Lawrey, Commented Feb 14, 2011 at 8:56

Steven Schlansker · Accepted Answer · 2011-02-14 04:48:43Z

6

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.

answered Feb 14, 2011 at 4:48

Steven Schlansker

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1 Comment

muddybruin Over a year ago

yep it's basically identical, except they used "value" instead of "a". See lines 38, and 83-85

Tom Hawtin - tackline · Accepted Answer · 2011-02-14 04:48:00Z

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".

answered Feb 14, 2011 at 4:48

Tom Hawtin - tackline

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Tom Hawtin - tackline Over a year ago

@ranjanarr Depends upon implementation. It's in the src.zip for the usual Oracle JDKs. The exact code has changed between updates.

Aravind Yarram · Accepted Answer · 2011-02-14 04:46:47Z

1

That means auto boxing is in place.

answered Feb 14, 2011 at 4:46

Aravind Yarram

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CoolBeans Over a year ago

@rananarr - Take a look at my comment.

Matthew Flaschen · Accepted Answer · 2011-02-14 04:59:15Z

0

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;

answered Feb 14, 2011 at 4:59

Matthew Flaschen

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