generaltype.java

java 的好东西,,开发的基本语言语法教程

import java.util.ArrayList;
import java.util.List;

public class GeneralType {
	public static void main(String[] args) {
		List<String> list = new ArrayList<String>();
		list.add("1");
		list.add("2");
		list.add("3");
		for (String str : list) {
			System.out.println(str);
		}
		
		//变量的泛型声明和方法的参数的泛型声明有很大差别!!
		List<Number> list2 = new ArrayList<Number>();
		list2.add(new Integer(1));
		list2.add(new Long(655));
		list2.add(new Double(234.44));
		prt1(list2);
		prt2(list2);
		
		List<Integer> list3 = new ArrayList<Integer>();
		list3.add(new Integer(1));
		list3.add(9);
//		prt1(list3);  //compile error
		prt2(list3);
	}
	//number类型
	private static void prt1(List<Number> list) {
		for (Number n : list) {
			System.out.println(n);
		}
	}
	//number 和子类 类型
	private static void prt2(List<? extends Number> list) {
		for (Number n : list) {
			System.out.println(n);
		}
	}
	
}