CODEWITHSUNDEEP
javapolymorphismpolymorphic-associations
KyelJmD
KyelJmD

Reputation: 4732

Polymorphism Assignment Statement

I have question regarding polymorphism about its assignment statement, for Example this is The Super class

   public class Person {

            private String firstName;
            private String middleInitial;
            private String lastName;
            private int age;

            public Person(String firstName,String middleInitial , String lastName , int age){
                setFirstName(firstName);
                setMiddleInitial(middleInitial);
                setLastName(lastName);
                setAge(age);
            }

            public void setFirstName(String firstName){
                this.firstName = firstName;
            }

            public String getFirstName(){
                return firstName;
            }

            public void setMiddleInitial(String middleInitial){
                this.middleInitial = middleInitial;
            }

            public String getMiddleInitial(){
                return middleInitial;
            }

            public void setLastName(String lastName){
                this.lastName = lastName;
            }

            public String getLastName(){
                return lastName;
            }

            public void setAge(int age){
                this.age = age;
            }

            public int getAge(){
                return age;
            }

            public String toString(){
                return String.format("First Name: "+getFirstName()+"\nMiddle Initial: "+getMiddleInitial()+
                                        "\nLast Name: "+getLastName()+"\nAge: "+getAge());
            }
    }

And this is The Derived Class

 public class Employee extends Person{

        private Contact contact;

        public Employee(String firstName,String middleInitial , String lastName , int age, Contact contact){
            super(firstName,middleInitial,lastName,age);
            this.contact = contact;
        }
public String toString(){
        return String.format(super.toString()+contact.toString());
    }
}

Now my question is what's the Difference Between these assignment statements ?? and what are the difference ? I know Employee is a Person but I want to know what's the difference between these two:

 Person employee1 = new Employee();
    Employee employee2 = new Employee();

and This

 Employee employeeKyle = new Employee();
    Person employeeKyel2 = employeeKyle;

I am kinda having a hard time about these .

Upvotes: 0

Views: 1682

Answers (3)

Guillaume
Guillaume

Reputation: 22822

In your second example, you only have one object, with two pointers to it. If you modify employeeKyle, then employeeKyle2 will be modified as well (they are the same object). The fact that you refers to employeeKyle2 as a Person and not an Employee is only helpful for the methods you're allowed to use on that reference. Under the hood, it's still pointing to the same Employee object, so if you later cast employeeKyle2 as an Employee, it will work and not throw a cast exception.

In the first example, you create two different objects, that's the only difference. They are two Employee objects under the hood, but you can only use Person methods on employee2.

Upvotes: 1

Dave Newton
Dave Newton

Reputation: 160191

The first one creates an Employee that is referenced as a Person, and an Employee referenced as an Employee. employee1 has only Person methods, while employee2 has both Person and Employee methods.

The second one creates an Employee and then creates a Person reference to the same Employee. Only methods defined in the Person class will be available to the employeeKyel2 instance, while employeeKyle will have all the Employee methods.

Upvotes: 1

leo
leo

Reputation: 1117

In the first one you have 2 OBJECTS, both are of the type Employee, and you have 2 different references to them, one being a Person reference and the other being an Employee reference.

In the second case, you have 1 OBJECT with 2 REFERENCES pointing to it, being one a Person and another an Employee.

The object is always of the type you've instantiated it with the new keyword (in this case, the object is always an employee). You can, however, have different types of references pointing to the actual object (the references can be either of the type of the object or of one of its superclasses).

Upvotes: 2

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