Java Immutable Class

An Immutable Class is one whose state can not be changed once created. There are provided rules to create a class immutable in Java. An immutable classes are those classes whose values are not changed.

There are certain guidelines given below :

1. Do not allow subclasses to override methods for Immutable Classes.
2. Special attention when having mutable instance variables for Immutable Classes.
3. Class is declared final so it cannot be extended.
4. Do not provide setter methods for Immutable Classes.
5. Class members name and date are private so cannot be accessed outside of class.
6. Does not contain any setter methods so outer class cannot change the class members.
7. Make all fields final and private for Immutable Classes.
8. Getter Method returns the copy of class members.
9. Class members are initialized using the constructor.

List of Immutable Classes in Java :

S.No.	Class Name	Package	S.No.	Class Name	Package
1	String	java.lang	2	Integer	java.lang
3	Byte	java.lang	4	Character	java.lang
5	Short	java.lang	6	Boolean	java.lang
7	Long	java.lang	8	Double	java.lang
9	Float	java.lang	10	StackTraceElement	java.lang
11	BigInteger	java.math	12	BigDecimal	java.math
13	File	java.io	14	Font	java.awt
15	BasicStroke	java.awt	16	Color	java.awt
17	GradientPaint	java.awt	18	LinearGradientPaint	java.awt
19	RadialGradientPaint	java.awt	20	Cursor	java.awt
21	Locale	java.util	22	UUID	java.util
23	Collections	java.util	24	URL	java.net
25	URI	java.net	26	Inet4Address	java.net
27	Inet6Address	java.net	28	InetSocketAddress	java.net

Create Immutable Class

package com.jaladhi.jst; public final class Immutable {
      private String name;
      private int date;
      Immutable(String name, int date) {
            this.name = name;
            this.date = date;
      }
      public String getName() {
            return name;
      }
      public int getDate() {
            return date;
      }
}
package com.jaladhi.jst;
public class ImmutableClass {
      public static void main(String args[]) {
            Immutable obj = new Immutable("Jaladhi Soft Technology", 2020);
            System.out.println("Name: " + obj.getName());
            System.out.println("Date : " + obj.getDate());
      }
}

Name : Jaladhi Soft Technology
Date : 2020

package com.jaladhi.jst;
import java.util.Date;
public final class ImmutableDemo {
      private final Integer intValue;
      private final String stringValue;
      private final Date dateValue;
      private ImmutableClass(Integer intValue, String stringValue, Date dateValue) {
            this.intValue = intValue;
            this.stringValue = stringValue;
            this.dateValue = new Date(date.getTime());
      }
      public static ImmutableDemo createNewInstance(Integer intValue, String stringValue, Date dateValue) {
            return new ImmutableDeo(intValue, stringValue, dateValue);
      }
      public Integer getIntValue() {
            return intValue;
      }
      public String getStringValue() {
            return stringValue;
      }
      public Date getDateValue() {
            return new Date(dateValue.getTime());
      }
      @Override
      public String toString() {
            return intValue +" - "+ stringValue +" - "+ dateValue;
      }
}
public class ImmutableDemoTest {
      public static void main(String[] args) {
            ImmutableDemo id = ImmutableDemo.createNewInstance(1000,"Jaladhi Soft Technology", new Date());
            System.out.println(id);
            tryToChange(id.getIntValue(),id.getStringValue(),im.getDateValue());
            System.out.println(id);
      }
      private static void tryToChange(Integer intValue, String stringValue, Date dateValue) {
            intValue = 10000;
            stringValue = "Jaladhi Soft Technology (JST).";
            dateValue.setDate(30);
      }
}

1000 - Jaladhi Soft Technology - Sat Dec 12 10:00:00 IST 2020
1000 - Jaladhi Soft Technology - Sat Dec 12 10:00:08 IST 2020