Java 8: Convert List to Map

In Java 8, you can use the Collectors.toMap() method to convert a List into a Map. Here is a simple example code:

Assume there is a class Person:

public class Person {
    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    // getters and setters
}

We currently have a List that we want to convert into a Map, with the key being the name and the value being the age.

import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class Main {

    public static void main(String[] args) {
        List<Person> personList = List.of(
                new Person("Alice", 25),
                new Person("Bob", 30),
                new Person("Charlie", 35)
        );

        Map<String, Integer> personMap = personList.stream()
                .collect(Collectors.toMap(Person::getName, Person::getAge));

        System.out.println(personMap);
    }
}

In the code above, we are using personList.stream().collect(Collectors.toMap(Person::getName, Person::getAge)) to convert a List into a Map, where the keys are names and the values are ages.

Please note that if there are duplicate keys in the List, an IllegalStateException exception will be thrown. You can use another overload of Collectors.toMap() method, specifying a merge function to handle duplicate keys.