Question

I want to have a Map object to contain specific value types.

Map<String,Object> foo = new HashMap<String,Object>();
foo.put("1",new Integer(1));
foo.put("2", new String("hello"):
for (Map.Entry<Integer, Integer> entry : foo.entrySet()) {
    if(entry.getValue() instanceof String) {
    //do something
    }
   else if(entry.getValue() instanceof Double) {
       //throw Exception
    }
}

You can see what i am trying to accomplish. I need specific Value types in my Map object so i don’t have to put lots of if/else statements. How do i accomplish this ?

Answer 1

If you don’t like the idea of having multiple maps, you can use the nice OOP feature called overriding.
see Override Methods for more information.

I would probably use composition pattern to wrap the value types and then define a interface for the action depending of the value types.

public abstract class ValueType {

    public abstract void valueSpecificAction(); 
}

public class DoubleValueType extends ValueType {

    private Double value;

    public DoubleValueType(Double value) {
            this.value = value;
    }

    public void valueSpecificAction() {
        //do double specific actions
    }
}

public class StringValueType extends ValueType {

    private String value;


    public void valueSpecificAction() {
        //do string specific actions


     }   
}

You can then add the objects of type ValueType in the maps.

Map<String,ValueType> foo = new HashMap<String,ValueType>();
foo.put("key1", new DoubleValueType(42.0));

later you can get the value, which has the type ValueType with the public method valueSpecificAction() which do the stuff depending on the specific type.