In Java, the HashMap class allows you to store key-value pairs where each key is unique. By default, HashMap allows storing any type of object as a value, including custom objects. This allows you to create a collection of custom objects and easily retrieve them using a specific key.

To use custom objects as values in a HashMap, you need to follow these steps:

Step 1: Create a Custom Object class

First, create a custom class that represents the object you want to store in the HashMap. Here is an example of a Person class with properties for name and age:

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

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

    // Getters and setters

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

Step 2: Create and Populate the HashMap

Next, create an instance of the HashMap class and populate it with custom objects. Here’s an example that creates a HashMap with String keys and Person objects as values:

import java.util.HashMap;

public class Main {
    public static void main(String[] args) {
        HashMap<String, Person> personMap = new HashMap<>();

        Person john = new Person("John Doe", 30);
        Person jane = new Person("Jane Smith", 25);

        personMap.put("John", john);
        personMap.put("Jane", jane);
    }
}

Step 3: Retrieve Objects from the HashMap

You can retrieve custom objects from the HashMap using the specified keys. Here’s an example that retrieves the Person object using the key "John":

Person retrievedPerson = personMap.get("John");
System.out.println(retrievedPerson.getName()); // Output: John Doe
System.out.println(retrievedPerson.getAge()); // Output: 30

Conclusion

Using custom objects as values in a HashMap allows you to organize and retrieve data effectively. By providing unique keys, you can easily access the objects stored in the HashMap. This feature enhances the flexibility and functionality of the HashMap class in Java.

For more details, refer to the official Java documentation on HashMap.

#java #hashmap