TextView textView = (TextView) findViewById(R.id.textView) is Upcasting or Downcasting?

Question

I am totally confused as to below code does upcast or downcast. If so how?

Is TextView a super class, I presume its a sub-type of View.

TextView textView = (TextView) findViewById(R.id.textView);

With buildgrade 3.0, you do not need cast this view. But TextView is a subview of View — Brian Hoang, Dec 31 '18 at 07:33
Textview is a subview of view and view itself extends object. Take a look at this: https://developer.android.com/reference/android/widget/TextView — Umair, Dec 31 '18 at 07:35

Mohammadreza Khatami · Accepted Answer · 2018-12-31T11:46:38.750

In short, It's down casting.

This line :

findViewById(R.id.textView);

Will return a view, But what kind of view it is ? (Button,List, TextView, ..) Look at this example :

public abstract class Car{
    public abstract void power();
}

public class BMW extends Car{
    public void power(){
        System.out.println(2200);
    }
}

public class Benz extends Car{
    public void power(){
        System.out.println(2100);
    }
}

Creating an object of above classes (BMW,Benz)

BMW bmw = new BMW();
Benz benz = new Benz();

public class CarFactory{

    public void create(Car car){
        if(car instanceof Benz)
            Benz benz = (Benz) car;
        else 
            BMW bmw = (BMW) car ;
    }
}

Both of them (Benz, BMW) are explicit cast, like TextView.

I hope this helps you

score 1 · Answer 2 · answered Dec 31 '18 at 07:35

1

its called DownCasting. you can understand deeply here

answered Dec 31 '18 at 07:35

Mayur Dabhi

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score 1 · Answer 3 · answered Dec 31 '18 at 07:36

TextView textView = (TextView) findViewById(R.id.textView);

The code you have mentioned is downcasting. Because findViewByID returns a View Object and TextView is a child of a View class. When casting from parent to child is called Down Casting While castinrg from child to Parent is called Upcasting.

Note: When you casting up, you normally do not need to cast cause of implicit casting.

TextView textView = (TextView) findViewById(R.id.textView) is Upcasting or Downcasting?

3 Answers3