Design an Immutable class that has an java.util.Date member

Upasana | May 19, 2019 | 1 min read | 2,273 views | Multithreading and Concurrency

In previous article we learned about immutable classes and their usecases

Design an Immutable class that has an java.util.Date member

As we know that java.util.Date is not immutable, we need to make a defensive copy of java.util.Date field while returning a reference to this instance variable.

Let’s create a hypothetical person class that has name and dob as the only two members.

Immutbale Person Class

import java.util.Date;

class Person {
    private String name;
    private Date dob;

    public Person(String name, Date dob) {
        this.name = name;
        this.dob = new Date(dob.getTime()); (1)
    }

    public String getName() {
        return name;
    }

    public Date getDob() {
        return new Date(dob.getTime()); (2)
    }
}

1	We are creating a new copy of Date field otherwise reference to dob field may leak
2	We are returning defensive copy of Date field instead of directly returning the reference of instance variable.