What does (TextView) (Button) do?

Question

This should be an easy question for someone who knows how it works.

TextView myText = (TextView) findViewById(R.id.myText);
Button btn = (Button) findViewById(R.id.button);

What does the (Textview)/(Button) do, what is it?

Is it equivalent to

TextView myText = new TextView(findViewById(R.id.myText));
Button btn = new Button(findViewById(R.id.button));

Also, I might be mistaken, but this is in the java language not only in android?

Thanks

Note: Im not asking what a textview or a button is, im asking is this a type of instantiation, casting, etc.

TextView myText = (TextView) findViewById(R.id.myText); is just intialization of textview. TextView myText = new TextView(activitycontext). you initialize your textview or button the one in closed braces `(TextView)` is casting to textview — Raghunandan, Jun 13 '13 at 14:52
If you want, post a reply so I can accept this as an answer. — problemo, Jun 13 '13 at 15:00

score 0 · Answer 1 · answered Jun 13 '13 at 14:52

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Well, the (Type) like (Button) or (TextView) is called a cast. You can easily find any information about casts in any language on Google.

answered Jun 13 '13 at 14:52

Quentin DOMMERC

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I know what casting is, I'm just not sure what putting it in that context actually does. – problemo Jun 13 '13 at 14:57
It's a cast, It just tells the system the view you're getting is a kind of what you're casting it. ;) – Quentin DOMMERC Jun 13 '13 at 15:08
:) Thanks! Somerandomstufftofillthelengthrequirement – problemo Jun 13 '13 at 17:31

score 0 · Answer 2 · answered Jun 13 '13 at 14:55

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Android is a platform, Java is the language used to write Android applications. So

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

is a cast (View -> TextView) in java and no, it isn't equivalent to use a constructor.

answered Jun 13 '13 at 14:55

spacifici

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score 0 · Answer 3 · answered Jun 13 '13 at 14:57

View.findViewById()

Returns View type, this View type could be TextView, Button or something else. By doing cast (Which is what () means), you are telling runtime that returned View is of type whatever in those braces.

TextView and Button are subclasses of View type.

Raghunandan · Accepted Answer · 2013-06-13T15:04:46.510

You are initializing textview

     TextView myText = (TextView) findViewById(R.id.myText);
     // the one in the braces is casting to textview

public final View findViewById (int id)

You can findViewById of the current view hierarchy set to the activity.

Look for a child view with the given id. If this view has the given id, return this view.

If you want to do it programatically

     TextView myText = new TextView(ActivityName.this);

If you do as above you need to add it to the root view

If you have LinearLayout as root view

     setContenView(R.layout.mylayout);
     LinearLayout ll = (LinearLayout) findViewById(R.id.linearlayout);   
     ll.addView(myText);

or

     setContentView(myText);

What does (TextView) (Button) do?

4 Answers4