自动打包与解包：

泛型：

上栗子：

TestMap1.java:

package com.zhj.www;
import java.util.*;public class TestMap {public static void main(String[] args) {Map m1 = new HashMap();Map m2 = new TreeMap();//m1.put("one", new Integer(1));m1.put("one", 1);     //auto-boxing//m1.put("two", new Integer(2));m1.put("two", 2);	//auto-boxing//m1.put("three",new Integer(3));m1.put("three", 3);//auto-boxing//m2.put("A",new Integer(1));m2.put("A", 1);//auto-boxing 基础类型的变量转化为对象//m2.put("B", new Integer(2));m2.put("B", 2);System.out.println(m1.size());//m1.size()=3System.out.println(m1.containsKey("one"));//System.out.println(m2.containsValue(new Integer(1)));System.out.println(m2.containsValue(1));if(m1.containsKey("two")) {//int i = ((Integer)m1.get("two")).intValue();int  i =(Integer)m1.get("two");//自动解包为IntegerSystem.out.println(i);}Map m3 = new HashMap(m1);m3.putAll(m2);System.out.println(m3);}
}

TestMap2.java:

package com.zhj.www;
import java.util.*;
/*相比于TestMap.java，我们开始使用泛型*/
public class TestMap2 {public static void main(String[] args) {Map<String, Integer> m1 =new HashMap<String,Integer>();Map<String, Integer> m2 =new HashMap<String,Integer>();m1.put("one", 1);     //auto-boxingm1.put("two", 2);	//auto-boxingm1.put("three", 3);//auto-boxingm2.put("A", 1);//auto-boxing 基础类型的变量转化为对象m2.put("B", 2);System.out.println(m1.size());//m1.size()=3System.out.println(m1.containsKey("one"));System.out.println(m2.containsValue(1));if(m1.containsKey("two")) {int i = m1.get("two");System.out.println(i);}Map<String, Integer> m3 = new HashMap<String,Integer>();m3.putAll(m2);System.out.println(m3);}
}

TestArgsWords.java:

package com.zhj.www;import java.util.*;public class TestArgsWords {private static final Integer ONE = new Integer(1);public static void main(String[] args) {//Map m = new HashMap();/*泛型*/Map<String, Integer> m =new HashMap<String,Integer>();for(int i = 0;i<args.length;i++) {Integer fred =(Integer) m.get(args[i]);//get 方法：返回key对应的value，如果不存在，则返回null.//m.put(args[i], (fred == null ? ONE: new Integer (fred.intValue()+1)));m.put(args[i], (fred == null ? ONE:fred+1));//自动打包}System.out.println(m.size()+"distinct words detected:");System.out.println(m);//put方法 ：将指定的key与value关联起来。}}