How to create Immutable Class and Object in Java. Writing or creating immutable classes in Java is becoming popular day by day, because. Immutable. objects offers several benefits over conventional mutable object, especially while. Java application. This Java String split example describes how Java String is split into multiple Java String objects. Immutable object not only guarantees safe. In fact JDK. itself contains several immutable classes like String, Integer and other wrapper. For those, who doesnt know what is immutable class or object. Immutable objects are those, whose state can not be changed once created e. String, once. created can not be modified e. Java Software Development and ObjectOriented Programming Paradigms A er learning the contents of this chapter, the reader would be able to understand. Java Interface are great ways to define abstraction in Java. By using interface in java you can write flexible and maintainable code which can adapt future. All modification in. String result in new object, seewhy String is immutable in Java. In this Java programming tutorial, we will learn, how to. Java or how to make a class immutable. By the way making. I also suggest reading. Java Concurrency in Practice. Immutable object. What is immutable class in Java. As said earlier, Immutable classes are those class, whose object can not be modified. String and String. Jumbo Solitaire Game. Buffer. Since. String is immutable class, any change on existing string object will result in. String, creating substring from String. What Is Object In Java With Example Program' title='What Is Object In Java With Example Program' />While in case of mutable object like String. Buffer, any. modification is done on object itself and no new objects are created. Some times. this immutability of String can also cause security hole, and that the reason why password should be stored on char. String. How to write immutable class in Java. Despite of few disadvantages, Immutable object still offers several. What Is Object In Java With Example Program' title='What Is Object In Java With Example Program' />Java code. Java 1. State of immutable object can not be modified after construction, any. All fields of Immutable class should be final. Object must be properly constructed i. Object should be final in order to restrict sub class for altering. By the way, you can still create immutable object by violating few rules. String has its hashcode in non final field. No matter how many times you calculate it. This. required a deep knowledge of Java memory model, and can create subtle race conditions if not. In next section we will see simple example of writing. Java. By the way, if your Immutable class has lots of optional and mandatory fields, then you can also use Builder design pattern to make a class Immutable in Java. Immutable Class Example in Java. Here is complete code example of writing immutable class in Java. We have. followed simplest approach and all rules for making a class immutable. Inheritance and Polymorphism. Contacts     privatefinal. String name    privatefinal. String mobile    public. ContactsString name, String mobile         this. Stringget. Name        return name        public. Stringget. Mobile        return mobile    This Java class is immutable, because its state can not be changed once. You can see that all of its fields are final. This is one of the most. Java, where all fields of class also. String in above case. Some time you may need to write. Date, despite. storing Date into final field it can be modifiedinternally, if. In order to preserve immutability in. Java best practice. Java, which includes mutable member. Immutable. Reminder    privatefinal. Date reminding. Date    public. Immutable. Reminder Date reminding. Date.         ifreminding. Date. get. Time lt System. Time. Millis            thrownew. Illegal. Argument. ExceptionCan not. Date                this. Date new. Datereminding. Date. get. Time        public. Dateget. Reminding. Date         return Date reminding. Date. clone    In above example of creating immutable class, Date is a mutable object. If get. Reminding. Date returns. actual Date object than despite reminding. Date being final variable, internals of. Date can be modified by client code. By returning clone or copy of. Date, we avoid that danger and preserves immutability of. Benefits of Immutable Classes in Java. As I said earlier Immutable classes offers several benefits, here are few. Immutable objects are by default thread safe, can be shared. Immutable object simplifies development, because its easier to share. Immutable object boost performance of Java application by reducing synchronization in code. Another important benefit of Immutable objects is reusability, you can cache Immutable object and reuse them, much like String literals and Integers. You can use static factory methods to provide methods like value. Of, which can return an existing Immutable object from cache, instead of creating a new one. Apart from above advantages, immutable object has disadvantage of. Since immutable object can not be reused and they are. String being a prime example, which can create lot of. Immutable object adds lot of. Thats all on how to write immutable class in Java. Java which involves mutable fields. Dont. forget to read more about concurrency benefit offered by Immutable object in. Java book recommended to Java programmers, Concurrency Practice in Java. Further Reading. Java Fundamentals, Part 1 and 2 Java Concurrency in Practice. Applying Concurrency and Multi threading to Common Java Patterns. Related Java programming concepts and tutorials. How do I copy an object in Java Basic Object Copying in Java. Let us Assume an object obj. Numbers Guessing Game Javascript more. Obj. 1 and contained. Obj. 2. shallow copying shallow copying creates a new instance of the same class and copies all the fields to the new instance and returns it. Object class provides a clone method and provides support for the shallow copying. Deep copying A deep copy occurs when an object is copied along with the objects to which it refers. Below image shows obj. Not only has obj. We can use Java Object Serialization to make a deep copy. Unfortunately, this approach has some problems toodetailed examples. Possible Problems clone is tricky to implement correctly. Its better to use Defensive copying, copy constructorsas egaga reply or static factory methods. If you have an object, that you know has a public clone method, but you dont know the type of the object at compile time, then you have problem. Java has an interface called Cloneable. In practice, we should implement this interface if we want to make an object Cloneable. Object. clone is protected, so we must override it with a public method in order for it to be accessible. Another problem arises when we try deep copying of a complex object. Assume that the clone method of all member object variables also does deep copy, this is too risky of an assumption. You must control the code in all classes. For example org. apache. Serialization. Utils will have method for Deep clone using serializationSource. If we need to clone Bean then there are couple of utility methods in org. Source. clone. Bean will Clone a bean based on the available property getters and setters, even if the bean class itself does not implement Cloneable. Properties will Copy property values from the origin bean to the destination bean for all cases where the property names are the same.