How to create an immutable class in Java?

Properties of immutable class objects cannot be modified after initialization. For example, String is an immutable class in Java. We can create an immutable class according to the following given rules.

• Declare the class as final-The class should be declared as final to prevent extension.

• Declare each field as final-Each field should be declared as final to prevent modification after initialization.

• Create getter methods for each field.−Create a public getter method for each field. Fields should be private.

• Each field has no setter method.−Do not create public setter methods for any fields.

• Create a parameterized constructor-Such a constructor will be used to initialize the properties once.

In the following example, we create an immutable class Employee.

Example

public　class　Tester　{
　　　public　static　void　main(String[]　args)　{
　　　　　　Employee　e　=　new　Employee(30,　"Robert");
　　　　　　System.out.println("Name:　"　+　e.getName()　+",　Age:　"　+　e.getAge());
　　　}
}
final　class　Employee　{
　　　final　int　age;
　　　final　String　name;
　　　Employee(int　age,　String　name)　{
　　　　　　this.age　=　age;
　　　　　　this.name　=　name;
　　　}
　　　public　int　getAge()　{
　　　　　　return　age;
　　　}
　　　public　String　getName()　{
　　　　　　return　name;
　　　}
}

Output Result

Name:　Robert,　Age:　30