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How to create the immutable class in Java?
An immutable class object's properties cannot be modified after initialization. For example String is an immutable class in Java. We can create a immutable class by following the given rules below.
Make class final − class should be final so that it cannot be extended.
Make each field final − Each field should be final so that they cannot be modified after initialization.
Create getter method for each field. − Create a public getter method for each field. fields should be private.
No setter method for each field. − Do not create a public setter method for any of the field.
Create a parametrized constructor − Such a constructor will be used to initialize properties once.
In following example, we've created a 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
Name: Robert, Age: 30
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