A preliminary study of Java generics

1. The understanding of the generic type

A high-level use of Java is the generic class, many basic frameworks will be built with generics, such as Gson ... Generics is really a good thing, but it is a sea of hundreds of rivers ... So as an Android developer it's more necessary to master this stuff.

Generics can be designed to return different types for a shared feature

Generics can be said to be a kind of constraint, can also be said to be a type of accommodation, extension ... I'm not saying it, it's purely personal understanding.

Constraint: Refers to the generic type if there is a specific type, then this is a constraint on the generic class, only to this specific type of work, ignoring all classes

Extension: The generic type that refers to is not a specific class type, but T, so it works for all class types.

2. The distinction of generic interfaces, generic classes, and generic methods

1, generic interface: In fact, and the normal interface is no different, is more than a generic, can be designed as a multi-purpose template interface, declared as follows:

/** *
 class Generator
 * @author ZHONGWR
 * *
 @param <T> * * Public
interface Generator<t> { Public
	T Next ();
}

2, generic class: And ordinary classes are no different, that is, more than a generic, can be designed for multi-purpose, a bit like a combination of classes: the declaration is as follows:

/** *
 Class Builder
 * * 
 @author ZHONGWR * * @param <T> * * Public
class basicgeneratorimp< T> implements generator<t> {
	private class<t> type;

	Public Basicgeneratorimp (class<t> type) {
		this.type = type;
	}

}

This is a generic class declaration that receives a class. class type.

3, generic methods: Needless to say, are routines, and the use of common methods is no different, is more than one generic parameter, the generic return value, so when the argument must give a definite type, otherwise the generic method has no meaning;

/**
	 * Generic method, used to create a class: A generic method is independent of a class and does not matter with the generic class entity class 
	 * ZHONGWR PM 9:08:13 
	 * generator<t> *
	public static <T> generator<t> Create (class<t> type) {return
		new basicgeneratorimp<t> ( type);
	

Universal generic method, so if you can, try to use the sea-na-Chuan generic method.

Next, use the Java programming idea: Finally, the demo of Java Engineering

Generic interface

/** *
 class Generator
 * @author ZHONGWR
 * *
 @param <T> * * Public
interface Generator<t> { Public
	T Next ();
}

/** *
 Class Builder
 * * 
 @author ZHONGWR
 * *
 @param <T>
* * public class Basicgeneratorimp<t> implements generator<t> {
	private class<t> type;

	Public Basicgeneratorimp (class<t> type) {
		this.type = type;
	}

	Public T Next () {
		try {return
			type.newinstance ();
		} catch (Exception e) {
			e.printstacktrace ();
			throw new RuntimeException ();
		}

	/**
	 * Generic method, used to create a class: A generic method is independent of a class and does not matter with the generic class entity class 
	 * ZHONGWR PM 9:08:13 
	 * generator<t> *
	public static <T> generator<t> Create (class<t> type) {return
		new basicgeneratorimp<t> ( type);
	}

Package type.coffee;

/** *
 Making Coffee class * * 
 @author Administrator */public
abstract class Coffee {
	private static int counter = 0;
	Private final Long id = counter++;

	Public String toString () {return
		getclass (). Getsimplename () + "" + ID;
	}
}

Import Type.coffee.Americano;
Import Type.coffee.Coffee;

/** *
 Test entrance * * 
 @author ZHONGWR * * @param <T> * * Public
class Maintest { Public
	static void Main (string[] args) {
		
		//Use generic methods to create generic class
		System.out.println ("className =" + Basicgeneratorimp.create (Americano.class). Next ());
	}

demo:http://download.csdn.net/detail/zhongwn/9651107