CODEWITHSUNDEEP
javagenerics
vho
vho

Reputation: 1141

How to call non generic method from a generic one

How to call non generic method from a generic one:

    class Test {
        ...
        public <T> int someFunction1(T someParam) {
            return someFunction2(someParam);
        }

        public int someFunction2(String someParam) {
           return 1;
        }

        public int someFunction2(Integer someParam) {
        return 1;
        }
    }

 Test t = new Test;
t.someFunction1(new String("1"));
t.someFunction1(new Integer(5));

Also is it possible to do this at compile time, rather than at runtime?

Upvotes: 4

Views: 867

Answers (4)

rapha&#235;λ
rapha&#235;λ

Reputation: 6523

The compiler can not determine that someParam in someFunction1 is either a String or an Integer. Something like this will work:

public <T extends String> int someFunction1(T someParam) {
    return someFunction2(someParam);
}

public int someFunction2(String someParam) {
    return 1;
}

If you wanted it to be String/Integer you would need to create some datatype or created overloaded definition of someFunction1 where T is bound to Integer

Or just some "ugly" casts:

public <T> int someFunction1(T someParam) {
    if (someParam instanceof Integer)
        return someFunction2((Integer) someParam);
    else if (someParam instanceof String)
        return someFunction2((String) someParam);
    else throw new IllegalArgumentException("Expected String or Integer")
}

Upvotes: 5

nick zoum
nick zoum

Reputation: 7285

This answer would only work if the the parameter is always a string or a Integer

public <T> int someFunction1(T someParam) {
    try {
        return someFunction2((String) someParam);
    } catch (ClassCastException e) {
        try {
            return someFunction2((int) someParam);
        } catch (ClassCastException ex) {
            return 0;
        }
    }
}

Upvotes: 0

Andy Turner
Andy Turner

Reputation: 140328

The generics don't add anything. You can (and should) remove the type variable from the method without changing behaviour:

public int someFunction1(Object someParam) {

and then apply one of the if/else instanceof chains proposed in the other answers.

Upvotes: 0

Zbynek Vyskovsky - kvr000
Zbynek Vyskovsky - kvr000

Reputation: 18825

You need to check the argument type and according to its type to explicitly cast and call correct method:

public <T> int someFunction1(T someParam) {
    if (someParam instanceof Integer)
        return someFunction2((Integer)someParam);
    else if (someParam instanceof String)
        return someFunction2((String)someParam);
    else
        throw new InvalidArgumentException("Unexepected type: "+someParam.getClass());
}

Upvotes: 4

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