How to automatically generate equals() and hashCode() methods using Records class in Java 14

How to automatically generate equals() and hashCode() methods using Records class in Java 14

In Java programming, we often need to write equals() and hashCode() methods for our classes. These two methods are very important when dealing with equality and hash codes of objects. To simplify this process, Java 14 introduces a new Records class. The Records class provides a simplified way to write equals() and hashCode() methods, and the implementation of these two methods can be automatically generated based on the member variables of the class. This article will introduce how to use the Records class in Java 14 to automatically generate equals() and hashCode() methods.

First, let's look at a simple example. Suppose we have a class named Person, which has two member variables: name and age. We want to be able to compare two Person objects for equality and the hash codes that generated them.

Before Java 14, we had to manually write the equals() and hashCode() methods, as shown below:

public 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 boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null || getClass() != obj.getClass()) {
            return false;
        }
        Person person = (Person) obj;
        return age == person.age && Objects.equals(name, person.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, age);
    }
}

The above code implements the equals() and hashCode() of the Person class method, but requires manually writing logic to compare member variables for equality and generate hash codes.

Now, let's use the Records class to simplify this process. We can directly use the Records keyword to define a class and specify its member variables. Then, the Records class will automatically generate implementations of the equals() and hashCode() methods for us. In this case, we can use the following code to define the Person class:

public record Person(String name, int age) {}

Yes, it’s that simple! With just one line of code, we define a Records class and automatically get the implementation of the equals() and hashCode() methods.

Now, let’s verify it:

public class Main {
    public static void main(String[] args) {
        Person person1 = new Person("Alice", 25);
        Person person2 = new Person("Alice", 25);
        Person person3 = new Person("Bob", 30);
        
        System.out.println(person1.equals(person2)); // 输出：true
        System.out.println(person1.equals(person3)); // 输出：false
        
        System.out.println(person1.hashCode()); // 输出：2035395
        System.out.println(person2.hashCode()); // 输出：2035395
        System.out.println(person3.hashCode()); // 输出：66181377
    }
}

As we can see, by using the Records class, we can easily compare two Person objects for equality and generate their Hash code. The equals() method of the Person class will automatically compare the equality of the two member variables name and age, and the hashCode() method will automatically generate a hash code based on name and age.

In addition, the Records class also provides a constructor, which we can use to instantiate objects and access their values ​​through member variables. For example, we can access the name and age of a Person object through person.name and person.age.

To summarize, using the Records class in Java 14 to automatically generate the equals() and hashCode() methods is a very simple and convenient way. We only need to define a Records class with one line of code, and then we can easily compare objects for equality and generate hash codes. This automatically generated method greatly simplifies code writing and improves development efficiency. Because of this, the Records class has become a very useful feature in Java 14.

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