Implementing generic interface in not generic class

Question

I want to implements a generic interface in a class. Consider implementing this generic interface:

public interface Lookup<T>{
  public T find(String name);
}

and this is the not generic class that implement Lookup:

public class IntegerLookup implements Lookup<Integer>{
  private Integer[] values;
  private String[] names;

  public IntegerLookup(String[] names, Integer[] values) {......}
  //now I want to write the implemented method - find

and my question is: how do I need to write this implemented method? I need to override it? yes?

public Object find(String name){...}

will be good? or:

public Integer find(String name){...}

Anywhere T is used in the super type, Integer should be used in the subclass that uses Integer as a type argument for T. — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Jul 10, 2014 at 17:17
@SotiriosDelimanolis but it was written Object not T in the super type... or I am getting wrong? — Yuval Levy
– Yuval Levy, Commented Jul 10, 2014 at 17:18
The super type, Lookup, has declared the method's return type as T. — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Jul 10, 2014 at 17:19
Do you want a utility method that looks up strings but returns a flexible type based on how it's called? — Bohemian
– Bohemian ♦, Commented Jul 14, 2014 at 7:31

Sotirios Delimanolis · Accepted Answer · 2018-04-30 14:53:48Z

3

The syntax here

public class IntegerLookup implements Lookup<Integer>{
//                                           ^

binds the type argument provided, ie. Integer, to the type variable declared by Lookup, ie. T.

So,

public Integer find(String name){...}

This is the same as doing

Lookup<Integer> lookup = ...;
lookup.find("something"); // has a return type of Integer

edited Apr 30, 2018 at 14:53

answered Jul 10, 2014 at 17:33

Sotirios Delimanolis

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Comments

Judge Mental · Accepted Answer · 2014-07-14 06:22:41Z

0

From your comments it sounds like you really want to use Object as the return type. I can't imagine why you would want to do that, but if so, you actually need to implement Lookup< Object >, not Lookup< Integer >.

But don't do that. Use Integer as the return type, since that type is standing in for T in your implementation.

answered Jul 14, 2014 at 6:22

Judge Mental

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