JDK 1.5 Characteristics Example 1 - Generics

Special note: Although Sun named the new version of JDK by Chinese habit 5.0, although the new version of the new version is so much, I still have to call new versions as JDK 1.5.

Generics is the most important feature of JDK 1.5, mainly to process Collection.

Detailed generics tutorial: http://java.sun.com/j2se/1.5/pdf/generics-tutorial.pdf.

The following code is debugged in JDK 1.5.

Code Example 1. Demo.java

Package maoxiang.examples.jdk15.generics;

Import java.util.arraylist;

Import java.util.collection;

Import java.util.hashmap;

Import java.util.linkedList;

Import java.util.list;

Import java.util.map;

/ **

* @Author Mao Xiang

*

* Demonstrate how to use the generics feature. The code comes from the generics tutorial:

* http://java.sun.com/j2se/1.5/pdf/generics-tutorial.pdf

*

* Generics is similar to Templates in C .

* the difference:

* 1.

* 2.

* /

Public class demo {

Public static void main (String [] args) {

}

/ **

* The simplest usage

* /

Public void test1 () {

// previous usage

// list myintlist = new linkedList (); // 1

//myintlist.add(new integer (0)); // 2

// integer x = (integer) MyintList.ITerator (). Next (); // 3 requires forced conversion

// 1.5 usage

List Myintlist = new linkedList (); // 1 '

Myintlist.add (new integer (0)); // 2 '

Integer x = MyintList.iterator (). Next (); // 3 '

}

/ **

* Usage of anonymous characters

* /

Public void test2 () {

List list = new arraylist ();

// Print a collection by anonymous character

Wildcards (List);

Wildcards1 ();

/ *

* If Wildcards2 is defined as Wildcards2 (List Shapes)

* The following call error

* /

Wildcards2 (List);

}

Public void Wildcards (Collection c) ​​{

// previous usage

// Iterator i = C.Itemrator ();

// for (int K = 0; k

//

Log (i.next ());

//}

//1.5 usage

// Collection C

For (Object E: C) {

Log (e);

}

}

Public void wildcards1 () {

// Collection C = new arraylist ();

//c.add (new object ()); // compile time error

// The above is a wrong usage, because the type of C cannot be determined, the add, but Get can. The correct usage is as follows: arraylist c = new arraylist ();

C.Add ("test");

List List = C;

LOG (C.Get (0));

}

Public Void Wildcards2 (List Shapes) {

// list Shapes Definition can only accept list shapes, or you cannot accept list

For (Shape S: Shapes) {

s.draw ();

}

// The following means is wrong, because the parameters are declared as Extends Shpape, and the Rectangle is not a SHAPE subclass, which belongs to unsecurity calls.

//shapes.add(0, new rectangle ());

Map alldrivers = new hashmap ();

Census.addRegistry (alldrivers);

// The following is allowed, because Drivers are clearly defined.

List Drivers = New ArrayList ();

Census.add (drivers);

}

/ **

* Generic Methods usage

*

* /

Public void test3 () {

/ / Suitable for various types of functions

Object [] OA = New Object [100];

Collection