Java将Map传递给varargs对

Question

Doing something like this with a normal array works:

public class TestVarArgs {
    public static void main(String[] args) {
        int[] array = new int[4];
        for (int i = 0; i < array.length; i++) {
            System.out.println(i);
        }
        testThis(array);
    }
    public static void testThis(int... args) {
        for (int i = 0; i < args.length; i++) {
            System.out.println(i);
        }
    }
}

Now how can I do this with maps?

I want to pass a map to a method that receives varargs of pairs.

Passing a Map to varargs of Entry.Map does not work.

Answer 1

Java varargs are equivalent to arrays, with compiler support that makes arrays behind the scene when calling the method.

If your method takes, say,

void myMethod(Map.Entry<String,String>>... args)

it is the same as

void myMethod(Map.Entry<String,String>>[] args)

so you could call it by inserting a conversion to array, like this:

Map<String,String> myMap = ...
...
myMethod((Entry<String,String>[])myMap.entrySet().toArray(new Map.Entry[myMap.size()]));

Answer 2

You can't pass a Collection to a varargs argument.
I think the easiest way is to create an array of key from the key set.

Map<K, V> aMap ;
Set<K> keySet = aMap.keySet();
K[] keyArray = keySet.toArray(new K[keySet.size()]);

aMethodWithVarargs(keyArray);

Of course, you can do this with the set of Entry.Map

Map<K, V> aMap ;
Set<Entry.Map<K, V>> entrySet = aMap.entrySet();
Entry.Map<K, V>[] entryArray = keySet.toArray(new Entry.Map<K, V>[keySet.size()]);

aMethodWithVarargs(entryArray);