Parent p=new Child() parent and child object reference in java

Parent p=new Child() ?

• By using parent reference, we can call only methods available in parent class and we can't call child specific methods.
• we can use parent reference to hold any child class object.

class Parent {
    int duplicateVariable = 10;
    String parentString = "parent string value";

    Parent() {
        System.out.println("parent Constructor");
    }

    public void duplicate_method() {
        System.out.println("duplicate method in Parent class");
    }

    public void parentMethod() {
        System.out.println("Parent method");
    }
}

class Child extends Parent {
    int duplicateVariable = 20;
    String childString = "child string value";

    Child() {
        System.out.println("child Constructor");
    }

    public void duplicate_method() {
        System.out.println("duplicate method in child class");
    }

    public void childMethod() {
        System.out.println("child method");
    }
}

public class ParentChildProgram {
    public static void main(String[] args) {
    Parent parentObj = new Child();
    System.out.println("Value=" + parentObj.duplicateVariable);// variable in parent class invoked
    parentObj.duplicate_method();// duplicate method in child class is invoked
    parentObj.parentMethod();
    System.out.println(parentObj.parentString);
  }
}

Output:

Parent p=new Child()

If we use parent reference to call specific child class specific methods we will get compile time error like below:

Parent P = new Child() compile time error
Child c=new Child() ?

By using child reference we can call both parent and class methods.
We can use child reference to hold only for that particular child class object only.

class Parent {
    int duplicateVariable = 10;
    String parentString = "parent string value";

    Parent() {
        System.out.println("parent Constructor");
    }

    public void duplicate_method() {
        System.out.println("duplicate method in Parent class");
    }

    public void parentMethod() {
        System.out.println("Parent method");
    }
}
class Child extends Parent {
    int duplicateVariable = 20;
    String childString = "child string value";

    Child() {
        System.out.println("child Constructor");
    }

    public void duplicate_method() {
        System.out.println("duplicate method in child class");
    }

    public void childMethod() {
        System.out.println("child method");
    }
}
public class ParentChildProgram {
    public static void main(String[] args) {
    Child childObj = new Child();
    System.out.println("Value=" + childObj.duplicateVariable);// variable in child class invoked
    childObj.duplicate_method();// duplicate method in child class is invoked
    childObj.parentMethod();
    childObj.childMethod();
    System.out.println(childObj.parentString);
    System.out.println(childObj.childString);
  }
}

Output:
Child c=new Child()
Please comment below to feedback or ask questions.