How to Create an Immutable Class

Posted in: How to Create an Immutable Class

To create an immutable class following steps should be followed:

1. Create a final class.
2. Set the values of properties using constructor only.
3. Make the properties of the class final and private
4. Do not provide any setters for these properties.
5. If the instance fields include references to mutable objects, don't allow those objects to be changed:
1. Don't provide methods that modify the mutable objects.
2. Don't share references to the mutable objects. Never store references to external, mutable objects passed to the constructor; if necessary, create copies, and store references to the copies. Similarly, create copies of your internal mutable objects when necessary to avoid returning the originals in your methods.

Example :

import java.util.Date;
	public final class BrokenPerson
	{
		private final String firstName;
		private final String lastName;
		private final Date dob;

		public BrokenPerson( String firstName,
		  String lastName, Date dob)
		{
			this.firstName = firstName;
			this.lastName = lastName;
			this.dob = dob;
		}

		public String getFirstName()
		{
			return this.firstName;
		}
		public String getLastName()
		{
			return this.lastName;
		}
		public Date getDOB()
		{
			return this.dob;
		}
	}