Question

In Java, suppose we have a function with the parameter double a. Does it work if I pass an integer as argument? (I mean, is there an implicit conversion?) And in the opposite case: if I have e.g. an integer as parameter, and I pass a double?

Unluckily, I am not able to compile my code at the moment, and I would like to check this assert.
Thank you for your attention.

Answer 1

See JLS – Section # 5.3 for details on Method Invocation Conversion.

Method invocation contexts allow the use of one of the following:

- an identity conversion (§5.1.1)
- a widening primitive conversion (§5.1.2)
- a widening reference conversion (§5.1.5)
- a boxing conversion (§5.1.7) optionally followed by widening reference conversion
- an unboxing conversion (§5.1.8) optionally followed by a widening primitive conversion.

So, your first invocation(int to double) will work fine according to rule # 2.

But the second invocation(double to int) will give Compiler Error, according to the statement quoted further in the same section: –

If the type of the expression cannot be converted to the type of the
parameter by a conversion permitted in a method invocation context,
then a compile-time error occurs.