使用地图确定键的数据类型-Java

Question

I have a method with a map as a passed in parameter. The key for the map will either be a Long or an Integer data type.

I am using the method map.containsKey() to check to see if a number being randomly generated as primitive type int is contained in the passed in map.

The problem occurs when the map's key is of type Long and map.containsKey() evaluates to false. Even if the map contains that int key value in Long form.

However if I try and cast the int to a long, the map expecteing an Integer will now have the same error.

I was wondering if there is a way to get the data type of a Map's key and then cast the generated number to that type so I can then use the map.containsKey() method?

I understand and wish I could just use a long as the key value for both maps, however that is not within the requirements of the assignment.

Appreciate any help.

Here is the code and the fields I am using

private TreeMap<Integer, LabClass> classes;
private HashMap<Long, Member> members;

public long generateUniqueNumber(AbstractMap map, int low, int high)
{
    Random rand = new Random();
    int number = OUT_OF_BOUNDS;
    int max = high - low + 1;

    if (map.size() < max)
    {
        do {
            number = rand.nextInt(max) + low;
        } while (map.containsKey(number) );
    }

    return number;
}

Answer 1

Just use Long as the key type and then there would be no need for casting. (Maybe you have a reason for not using Long as the key)

Answer 2

You can get a data type from an Object by using .getClass() and check if it is an integer or a long.

Unless you are doing something very big and you are trying to conserve data, you should cast all the integers to longs when adding them to the map. Remember, an integer can be a long, but a long can not be an integer unless the long is within the integer's max size.

Answer 3

The easiest solution would be to change your while statement:

while (map.containsKey(number) || map.containsKey((long) number))

Since the keys might be Integers or might be Longs, you might as well check if either type of key is present.

Update: The contract for the containsKey method states that it may throw a ClassCastException "if the key is of an inappropriate type for this map." So my answer is not viable.

Answer 4

for (Long key : map.keySet()) {
     // check if int i == (int) (long) key;
}