How can I expand arguments in Java?

Question

The following Python snippet does exactly what I mean:

def function(a, b, c):
    print("%i :: %s :: %f" % (a,b,c))

a = 1
b = "abc"
c = 1.0

function(a, b, c)

list = [a, b, c]

# This is what I am searching for in Java
function(*(list))

So I have one list-like structure and I don't know how many arguments it has, but I know that it has the right number of arguments with the right type and format. And I want to pass them to a method. So I have to "expand" those arguments. Does anybody know how to do so in Java?

Answer 1

Java doesn't have this facility, since as a statically, strongly-typed language it's uncommon for a method to take a collection of values of uniform type that could all be stored in some composite object (array, list, etc.). Python doesn't have this problem because everything is dynamically-typed. You can do this in Java by defining a helper method that takes a single object in holding all the parameters, then expands them out in a call to the real method.

Hope this helps!

Answer 2

You could declare optional parameters with Object... such that you can pass an arbitrary number of arguments and then cast each of them to the required type:

public void method1(String p1, Integer p2) {
}

public void method2(Object... params) {
    method1((String)params[0], (Integer)params[1];
}

You can call method2 as:

method2("abc", 1);

Of course, this example is a bit redundant, because you could directly call method1, but that's not what I wanted to illustrate. :)

Answer 3

You can't. In Java, method parameters are checked at compile time, and since the content of the array is only defined at runtime, this check would be impossible.

Your closest solution is to have a method taking an array as a parameter, and eventually expanding the arguments to place a call to the targeted method.