CODEWITHSUNDEEP
kotlin
Mahabub
Mahabub

Reputation: 531

Java 8 lambda to kotlin lambda

public class Main {
    static class Account {
        private Long id;
        private String name;
        private Book book;

        public Account(Long id, String name, Book book) {
            this.id = id;
            this.name = name;
            this.book = book;
        }

        public String getName() {
            return name;
        }
    }
    public static void main(String[] args) {
        List<Account> data1 = new ArrayList<>();
        data1.add(new Account(1L,"name",null));
        List<String> collect = data1.stream().map(account -> account.getName()).collect(Collectors.toList());

        System.out.println(collect);
    }
}

In the above code I am trying to convert the following line

List<String> collect = data1.stream().map(account -> account.getName()).collect(Collectors.toList());

into kotlin code. Kotlin online editor gives me the following code

 val collect = data1.stream().map({ account-> account.getName() }).collect(Collectors.toList())
    println(collect)

which gives compilation error when i try to run it.

how to fix this???

or what is the kotlin way to get list of string from list of Account Object

Upvotes: 5

Views: 2265

Answers (2)

Jayson Minard
Jayson Minard

Reputation: 85946

As @JBNizet says, don't use streams at all, if you are converting to Kotlin then convert all the way:

List<String> collect = data1.stream().map(account -> account.getName()).collect(Collectors.toList());

to 

val collect = data1.map { it.name } // already is a list, and use property `name`

and in other cases you will find that other collection types can become lists simply with toList() or to a set as toSet() and so on. And everything in Streams has an equivalent in Kotlin runtime already.

There is no need for Java 8 Streams at all with Kotlin, they are more verbose and add no value.

For more replacements to avoid Streams, read: What Java 8 Stream.collect equivalents are available in the standard Kotlin library?

You should read the following as well:

And maybe this is a duplicate of: How can I call collect(Collectors.toList()) on a Java 8 Stream in Kotlin?

Upvotes: 1

JB Nizet
JB Nizet

Reputation: 691685

Kotlin collections don't have a stream() method.

As mentioned in https://youtrack.jetbrains.com/issue/KT-5175, you can use

(data1 as java.util.Collection<Account>).stream()...

or you can use one of the native Kotlin alternatives that don't use streams, listed in the answers to this question:

val list = data1.map { it.name }

Upvotes: 12

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