Java overriding methods when creating new instance of a class

Question

This might be simple for seasoned java developers but I just cant seem to figure it out. I read a post from here. The code was

View v = new View(this) {     @Override     protected void onDraw(Canvas canvas) {         System.out.println("large view on draw called");         super.onDraw(canvas);     } }; 

It was an Android question. Here the user creates an instance of a view and overrides a method in a single line. Is there a name for this kind of coding?

My second doubt is, he overrides a protected method from another package. Isn't protected mean package private. I know this will work as I tried it out but I just couldn't figure out why it worked. So why is this code working?

I did try to google this and search in SO before asking but couldn't figure out an answer.

Answer 1

protected means (roughly) "available to sub-classes". (See this table.) Since the new View(this) { ... } creates a subclass, it is possible to override the method within it.

In this case it doesn't matter that you're in a different package. (See the protected line and second column in this table.) The fact that the method is in a subclass is sufficient to "get access" to a protected method.

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Potential follow-up question: What sense does it make, if I can't call the method anyway?

All methods in Java are virtual. This means that whenever the View class performs a seemingly internal call to the onDraw method, this call will be dispatched to the overridden method.

Answer 2

That is not exactly a kind of coding. That is a Java anonymous class. It is very common in Android and in general with event listeners and that kind of stuff.

For more details you can read this link (probably not the best one):

The anonymous inner classes is very useful in some situation. For example consider a situation where you need to create the instance of an object without creating subclass of a class and also performing additional tasks such as method overloading.

About your second question, the keyword protected means that the method is only available to subclasses, so it is possible to override the method.