Passing int to a method taking Integer as parameter?

Question

Is it Ok to pass int to a method which is taking Integer as parameter. Here is the code

public class PassingInt 
{
    public static void main(String args[])
    {
        int a = -1;
        passIntToInteger(a);//Is this Ok?
    }

    private static void passIntToInteger(Integer a) 
    {
        System.out.println(a);
    }

}

Yes it works. You could also do passIntToInteger(new Integer(a)); — Pphoenix
– Pphoenix, Commented Jul 9, 2014 at 14:01
@Pphoenix Always use valueOf with the wrappers instead of new. — chrylis -cautiouslyoptimistic-
– chrylis -cautiouslyoptimistic-, Commented Jul 9, 2014 at 14:03
@chrylis: Thank you! Is there a reason to always do so, or is it just standard? :) — Pphoenix
– Pphoenix, Commented Jul 9, 2014 at 14:04
@Pphoenix It is actually a performance improvement (micro optimization). valueOf uses a cache for some "common" values, i.e. -127 to +127 internally - that means no object creation needs to happen for these values. One general piece of advice to the OP is to generally avoid using auto-boxing and wrapped types when possible because it hides things that are happening and can bite back: You can get a NullPointerException when unboxing an Integer wrapper type that is null for example. The equals method also has some quirks when working with longs if I remember correctly. — PermaFrost
– PermaFrost, Commented Jul 9, 2014 at 14:07

peter.petrov · Accepted Answer · 2014-07-09 14:14:52Z

7

Yes, it is OK, it will be auto-boxed.

The reverse is also OK and is called auto unboxing.

More info here:

Autoboxing and Unboxing

edited Jul 9, 2014 at 14:14

answered Jul 9, 2014 at 14:01

peter.petrov

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Comments

Pang · Accepted Answer · 2018-10-12 03:26:25Z

5

Yes, it is.

Why? Because of auto-boxing. Primitives are converted to an object of its corresponding wrapper class. From Java Tutorials:

Autoboxing is the automatic conversion that the Java compiler makes between the primitive types and their corresponding object wrapper classes. For example, converting an int to an Integer, a double to a Double, and so on.

In your case:

primitive type: int -> wrapper class: Integer

edited Oct 12, 2018 at 3:26

Pang

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answered Jul 9, 2014 at 14:03

Christian Tapia

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Comments

FrancescoDS · Accepted Answer · 2014-07-09 14:12:41Z

1

Yes it is possible to do it, and it is possible to do also the opposite (from Integer to int)

answered Jul 9, 2014 at 14:12

FrancescoDS

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Comments

Elliott Frisch · Accepted Answer · 2014-07-09 14:21:45Z

Yes, in your example it would be autoboxed (converted from an int primitive to an Integer object) -

public static void main(String args[]) {
    int a = -1;
    passIntToInteger(a); // <-- Auto Boxing
}

private static void passIntToInteger(Integer a) {
    System.out.println(a);
}

Java also has (auto-)unboxing (converting from an Integer object to an int primitive) -

public static void main(String args[]) {
    Integer a = -1;
    passIntegerToInt(a); // <-- Auto Un-Boxing
}

private static void passIntegerToInt(int a) {
    System.out.println(a);
}

This allows you to use primitives with collections, otherwise List<Integer> could not store int(s) (for example).

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