record.md

Record

Java 14 introduce a new keyword record to bring Kotlin data class like feature in Java.

Before Java 14, a simple POJO for storing data could like this.

class Person {

    private String name;
    private int age;

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

    public int getAge() {
        return age;
    }

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

    public String getName() {
        return name;
    }

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

    @Override
    public int hashCode() {
        int hash = 7;
        hash = 97 * hash + this.age;
        hash = 97 * hash + Objects.hashCode(this.name);
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final Person other = (Person) obj;
        if (this.age != other.age) {
            return false;
        }
        if (!Objects.equals(this.name, other.name)) {
            return false;
        }
        return true;
    }

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

}

The Person class consists of constructor, fields, getters, setter, equals, hashCodes and toString method.

Use record in Java 14, it can be simplified as.

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

You can add an alternative constructor, or add additional checking to the default constructor.

public record RecordPerson( String name, int age) {
	public RecordPerson{
		if(age <= 0) {
			throw new IllegalArgumentException(
                "The age of a person must be positive");
		}
	}
	public RecordPerson(String name){
		this(name, 20);
	}
}

You can access the name and age like this.

RecordPerson person14 = new RecordPerson("Person in Java 14", 15);

System.out.println("Person in Java 14:\n" + person14);

System.out.println("Person'name in Java 14:\n" + person14.name());
System.out.println("Person'age in Java 14:\n" + person14.age());

Test the equals method.

RecordPerson person14Copy = new RecordPerson(person14.name(), person14.age());
System.out.println("Person.equals in Java 14:\n" + person14Copy.equals(person14));

You should use an extra --enable-preview parameter to compile and run this application.

There are some limitations in a record class.

• A record class can not extend other classes.
• And it can not be inherited by other classes.
• And all fields in a record imply final, that means once a record is instantiated, all fields can not be changed.

Use javap to decompile the RecordPerson.class file.

#javap  com.example.demo.RecordPerson
Compiled from "RecordPerson.java"
public final class com.example.demo.RecordPerson extends java.lang.Record {
  public com.example.demo.RecordPerson(java.lang.String, int);
  public com.example.demo.RecordPerson(java.lang.String);
  public java.lang.String toString();
  public final int hashCode();
  public final boolean equals(java.lang.Object);
  public java.lang.String name();
  public int age();
}
   

As you see it is declared as final and extends java.lang.Record.

A record class is useful to transfer data between layers in multi-layered enterprise applications, aka it a good match with the DTO(Data Transfer Object) pattern.