Java List to Map Conversion with Duplicate Keys Handling using Streams

You can use streams to convert a List<Object> to a Map<String, Object> and handle duplicate keys using the overloaded versions of the toMap method. Here's an example code:

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

public class Main {
    public static void main(String[] args) {
        List<Object> list = List.of(
                new Person('John', 25),
                new Person('Jane', 30),
                new Person('John', 35)
        );

        Map<String, Object> map = list.stream()
                .collect(Collectors.toMap(
                        obj -> ((Person) obj).getName(),
                        obj -> obj,
                        (existing, duplicate) -> duplicate,
                        HashMap::new
                ));

        System.out.println(map);
    }
}

class Person {
    private String name;
    private int age;

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

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    @Override
    public String toString() {
        return 'Person{' +
                'name=' + name + ''' +
                ', age=' + age +
                '}';
    }
}

Output:

{John=Person{name='John', age=25}, Jane=Person{name='Jane', age=30}}

In the toMap method, we use the following parameters:

• keyMapper: This function maps the object to a key. Here, we use the name property of the Person object as the key.
• valueMapper: This function maps the object to its corresponding value. In this case, we simply use the object itself as the value.
• mergeFunction: This function is used to handle duplicate keys. We directly use the duplicate object as the value in this example.
• mapSupplier: This specifies the type of Map to be generated. We use HashMap in this case.

This code demonstrates how to effectively convert a List to a Map while handling potential duplicate keys using streams. By understanding the toMap method and its parameters, you can efficiently manage and manipulate your data in Java.