Java syntax with greater than/less than: <> are they class specific?

Question

I've been doing an Android tutorial and encountered a class with the following:

public class ImageAndTextAdapter extends ArrayAdapter<String> {

Is the <String> a form of inheritance by type? Or is it some other Java syntax that I should know about?

The class is:

android.widget.ArrayAdapter<String>

Answer 1

This is called generics . The class within < and > is a type parameter .

This is easiest explained by an example:

An ArrayList can store items. If you specify a type parameter like this: ArrayList<String> then this array list will store items of String type only, (in other words, it will store String s only)!

Similarly, the ArrayAdapter is "parameterized" by a type as well. The ArrayAdapter probably holds a value, and this value will be of the type specified between < and > , which in your case is String .

Useful links:

• Official trail on Generics (a good starting point)

Answer 2

That's Java Generics .

It's like C++ templates.

It says that the ArrayAdapter is backed by an array of Strings. It's mostly useful so when you get/add objects, it's type-safe and you don't have to perform any casting.

Answer 3

This is part of Generics which was introduced in Java1.5, Sometimes you don't know what type of object you can pass or get, so you can pass a generic type of object "?" . In this particular instance, you are passing ArrayAdapter object which contains String objects. you can read more http://en.wikipedia.org/wiki/Generics_in_Java

Answer 4

This is a Java generic class.

http://download.oracle.com/javase/tutorial/java/generics/index.html