Java Instantiate new Map.Entry-array

Question

I'm having problems casting an object array to a key-value pair array, with generic types for the key and value objects. Here is a minimal example.

public class Main {
    public static void main(String[] args) {
        array = (Map.Entry<Integer, Integer>[]) new Object[1];
    }

    private static Map.Entry<Integer, Integer>[] array;
}

Changing Map.Entry to a class (rather than interface) doesn't do the trick either.

Error trace:

run:
Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.util.Map$Entry;
        at lab2.Main.main(Main.java:13)
Java Result: 1

Why would you think that new Object[1] is type compatibile with Map.Entry<Integer, Integer>[]? Of course a new vanilla Object[] array cannot be cast to something more specific. In the same way that this is not legal either: (String)new Object();. — Kirk Woll
– Kirk Woll, Commented Nov 2, 2010 at 16:51

jjnguy · Accepted Answer · 2010-11-02 17:00:29Z

3

Do you need to have an array? You can do the following with a List:

public static void main(String[] args) {
    array = new ArrayList<Map.Entry<Integer, Integer>>();
}

private static List<Map.Entry<Integer, Integer>> array;

Alternately, you can instantiate the non generic type, and cast to the generic type:

public static void main(String[] args) {
    array = (Map.Entry<Integer, Integer>[])new Map.Entry[1];
}

private static Map.Entry<Integer, Integer>[] array;

However, this will give you warnings, and is generally not preferred.

edited Nov 2, 2010 at 17:00

answered Nov 2, 2010 at 16:54

jjnguy

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