CODEWITHSUNDEEP
javalambdajava-8
Naveen Kumar
Naveen Kumar

Reputation: 422

Java 8 predicate generic function is not accepting List of Integers

I have one filter Method using Predicate Interface to filter List on some conditions.

public static <T> List<T> filter(List<T> list,Predicate<T> predicate){
    List<T> result=new ArrayList<T>();
    for(T t:list){
        if(predicate.test(t)){
            result.add(t);
        }
    }
    return result;
}

I have one Integer array List as List arraIntegerList=Arrays.asList(1,2,3,3,4);

While calling above method it is giving compilation error.

System.out.println(filter(arraIntegerList,(int i)->(i>2)));

Why It is giving compilation error while same list with String is working fine.

Upvotes: 2

Views: 2010

Answers (2)

A N M Bazlur Rahman
A N M Bazlur Rahman

Reputation: 2300

The lambda parameter types must exactly match with the method description. Since (int i) doesn't match with the generic method description filter(List<T> list,Predicate<T> predicate) and generics doesn't work with primitives. So you need to provide the parameterized type. 

    System.out.println(filter(arraIntegerList, (Integer i) -> (i > 2)));

And you can let the compiler to infer the type though. In that case you can write - 

    System.out.println(filter(arraIntegerList, i -> (i > 2)));

Upvotes: 0

Eran
Eran

Reputation: 393841

You need to give the List a parameterized type, and the lambda's parameter must match the parameter of the List.

For example, this works :

List<Integer> arraIntegerList=Arrays.asList(1,2,3,3,4);
System.out.println(filter(arraIntegerList,(Integer i)->(i>2)));

Output :

[3, 3, 4]

As Stuart Marks commented, this also works :

List<Integer> arraIntegerList=Arrays.asList(1,2,3,3,4);
System.out.println(filter(arraIntegerList,i->(i>2)));

Upvotes: 4

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