“公共抽象类SampleAdapter”是什么意思 <T extends Adapter> 扩展ViewGroup”？

Question

I am not getting meaning by

public abstract class  SampleAdapter <T extends Adapter> extends ViewGroup

What does it do? In general we perform normal inheritance, but here something extended form. can any body suggest me?

thanks

Answer 1

This declares a class SampleAdapter that:

• has public visibility
• is abstract ; it cannot be instantiated directly; it must be be used as a base class.
• is generic ; it must be parameterised by some type T that is a sub-class of Adapter .
• inherits from ViewGroup .

Answer 2

T extends Adapter :

The class SampleAdapter takes a class parameter T that should extend Adapter

example :

ArrayList A = new ArrayList<String>();

String is parameter for ArrayList.

SampleAdapter A = new SampleAdapter<parameterClass> ();

parameterClass is parameter for SampleAdapter (which is T) and it must extend Adapter :

public class parameterClass extends Adapter{//must extend Adapter

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As for abstract , it says that class SampleAdapter is a class that can't be instantiated directly but rather must be extended by another class.

Answer 3

The thing inside the < > section is associated a concept called "generics". It's a feature introduced in Java from Java 5 and forward. You can read more here .

Answer 4

abstract is referring to a class that can't be instantiated directly, usually because of some methods that need to be implemented in an extending class.

You'll have to implement those abstract methods in the subclass, otherwise your code won't compile.

Answer 5

abstract means that the SampleAdapter class cannot have any objects, <T extends Adapter> means, that the SampleAdapter class is used as a container for objects of any class, that extends Adapter . Hope this helps.