Java中方法重载中的Varargs

You can either

Widen

or

Box

but you cannot do both, unless you are

boxingand widening

to

Object

(An int to Integer(Boxing) and then Integer to
Object(Widening) is legal, since every class is a subclass of

Object

, so it
is possible for

Integer

to be passed to

Object

parameter)

Similarly an

int

to

Number

is also legal (int -> Integer -> Number) Since
Number is the super class of

Integer

it is possible.

Let’s see this in your example: -

public static void test(Integer...i)public static void test(Float...f)

There are some rules that are followed when selecting which overloaded method
to select, when Boxing, Widening, and Var-args are combined: -

1. Primitive widening uses the

   smallest

   method argument possible
2. Wrapper type cannot be widened to another Wrapper type
3. You can Box from int to Integer and widen to Object but no to Long
4. Widening beats Boxing, Boxing beats Var-args.
5. You can Box and then Widen (An

   int

   can become

   Object

   via

   Integer

   )
6. You cannot Widen and then Box (An

   int

   cannot become

   Long

   )
7. You cannot combine var-args, with either widening or boxing

So, based on the above given rules: -

When you pass two integers to above functions,

• according to rule 3, it will have to be first

  Widened

  and then

  Boxed

  to fit into a

  Long

  , which is illegal according to rule 5 (You cannot Widen and then Box).
• So, it is Boxed to store in

  Integer

  var-args.

But in first case, where you have methods with

var-args

of primitive types:

public static void test(int...i)public static void test(float...f)

Then

test(1, 2)

can invoke both the methods (Since neither of them is more
suitable for

rule 1

to apply) : -

• In first case it will be

  var-args

• In second case, it will be Widening and then Var-args (which is allowed)

Now, when you have methods with exactly one int and one flost: -

public static void test(int i)public static void test(float f)

Then on invoking using

test(1)

, rule 1 is followed, and smallest possible
widening (i.e. the

int

where no widening is needed at all) is chosen. So 1st
method will be invoked.

For more information, you can refer to

JLS - Method InvocationConversion