Generics and BiPredicate with incorrect return type

Question

While following a course for

Java 8

we're now onto the topic of

Generics

and

Lambda expressions

. We've been asked to make the following method

Generic

and not

String

only:

public static String betterString(String s1,String s2,IBetterString bs){

    if(bs.isBetter(s1, s2)){

        return s1;

    }else{

        return s2;

    }

}

What I made of this so far is the following:

public static <T> betterEllement(T s1, T s2, BiPredicate<T, T> bi) {

    if (bi.test(s1, s2)) {

        return s1;

    } else {

        return s2;

    }

}

But it appears that my

Return type

according to Intellij is incorrect. I don't really understand why that is, because I defined

<T>

as a return type for this method. Sorry if this is a stupid question, I'm just a beginner and would like to understand why it's not correct.

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Answer 1

Because you return nothing using your method. <T> define it's a generic Type which is not known yet. That doesnt mean that you return it. You need to add another T which is the generic Type return value.

Its

public static <T> T betterEllement(T s1, T s2, BiPredicate<T, T> bi) {
    if (bi.test(s1, s2)) {
        return s1;
    } else {
        return s2;
    }
}

<T> can also be used if you know the return value but want to define generic arguments.

public static <T> String getStringTest(T test) { 
  if (test.getClass().isInstance(WhatEver.class)) { ....} 
  return "test"; 
}

You can see it perfectly using a generic Class.

class TestGeneric<T> {
    public T betterElement(T s1) { /** .. **/ return null; }
}

Generics and BiPredicate with incorrect return type

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