Java 泛型举例

kanglecjr

Java 5 之后引入泛型（Genetics）。

使用泛型的入门例子：
package generics;import java.util.*;public class Eg01 {public static void main(String[] args){List<Integer> myIntList = new LinkedList<Integer>(); myIntList.add(new Integer(0));Integer x = myIntList.iterator().next(); // 3System.out.println(x);}}
解释：因为使用泛型语法，// 3  处不必进行Integer类型强制转换。

泛型的简单定义：
package generics.define;public interface List<E> {void add(E x);Iterator<E> iterator();}interface Iterator<E> {E next();boolean hasNext();}

有边界的通配符：
package generics.boundedwildcards;import java.util.*;public class Census{public static void addRegistry(Map<String, ? extends Person> registry){}public static void main(String[] args){Map<String, Driver> allDrivers = new HashMap<String, Driver>();Census.addRegistry(allDrivers);}}class Driver extends Person{}class Person{}
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package generics.boundedwildcards;public abstract class Shape{public abstract void draw(Canvas c);}


package generics.boundedwildcards;public class Circle extends Shape{private int x, y, radius;public void draw(Canvas c){}}
package generics.boundedwildcards;public class Rectangle extends Shape{private int x, y, width, height;public void draw(Canvas c){}}
package generics.boundedwildcards;import java.util.List;public class Canvas {public void draw(Shape s){s.draw(this);}//public void drawAll(List<Shape> shapes){public void drawAll(List<? extends Shape> shapes){for(Shape s : shapes){s.draw(this);}}}