实现将一个List转化为Map<Key,List>的样式

   
  
import java.util.ArrayList;   
import java.util.HashMap;   
import java.util.Iterator;   
import java.util.List;   
import java.util.Map;   
import java.util.Set;   
  
/**  
 * 类List4Map.java的实现描述：List4Map.java  
 *   
 * @author ahhqcheng 2012-2-29 下午7:56:11  
 */  
public class List4Map {   
  
    /**  
     * @description 实现将一个List转化为Map<Key,List>的样式  
     * @param 某个对象的List  
     * @return Map<Key,List>  
     */  
    public Map<Integer, List<TestObject>> list4Map(List<TestObject> list) {   
  
        Map<Integer, List<TestObject>> map = new HashMap<Integer, List<TestObject>>();   
  
        if ((list != null) && (list.size() != 0)) {   
            for (TestObject test : list) {   
                // 这一步是关键，也很巧妙吧，哈哈   
                List<TestObject> testList = map.get(test.getId());   
                if (testList == null) {   
                    testList = new ArrayList<TestObject>();   
                }   
                testList.add(test);   
                map.put(test.getId(), testList);   
            }   
        }   
        return map;   
    }   
  
    /**  
     * @description 对Map<key,List>的数据结构进行遍历  
     * @param Map<key,List>  
     * @return void  
     */  
    public void outOfMap(Map<Integer, List<TestObject>> map) {   
        Set<Integer> keySet = map.keySet();   
        for (Iterator<Integer> i = keySet.iterator(); i.hasNext();) {   
            Integer key = i.next();   
            System.out.println(key + "  :  ");   
            List<TestObject> testList = map.get(key);   
            for (TestObject test : testList) {   
                System.out.print("<--" + test.getName() + "--" + test.getAddress() + "-->");   
            }   
            System.out.println();   
        }   
  
    }   
  
    public static void main(String[] args) {   
        List4Map list4Map = new List4Map();   
  
        /**  
         * 构造数据  
         */  
        List<TestObject> list = new ArrayList<TestObject>();   
        TestObject test1 = list4Map.new TestObject(1, "name1", "address1");   
        TestObject test2 = list4Map.new TestObject(1, "name2", "address2");   
        TestObject test3 = list4Map.new TestObject(1, "name3", "address3");   
        TestObject test4 = list4Map.new TestObject(2, "name1", "address1");   
        TestObject test5 = list4Map.new TestObject(2, "name2", "address2");   
        TestObject test6 = list4Map.new TestObject(2, "name3", "address3");   
  
        list.add(test1);   
        list.add(test2);   
        list.add(test3);   
        list.add(test4);   
        list.add(test5);   
        list.add(test6);   
  
        // 装换   
        Map<Integer, List<TestObject>> map = new HashMap<Integer, List<TestObject>>();   
        map = list4Map.list4Map(list);   
  
        // 输出   
        list4Map.outOfMap(map);   
  
    }   
  
    class TestObject {   
  
        private int    id;   
        private String name;   
        private String address;   
  
        public int getId() {   
            return id;   
        }   
  
        public void setId(int id) {   
            this.id = id;   
        }   
  
        public String getName() {   
            return name;   
        }   
  
        public void setName(String name) {   
            this.name = name;   
        }   
  
        public String getAddress() {   
            return address;   
        }   
  
        public void setAddress(String address) {   
            this.address = address;   
        }   
  
        public TestObject(int id, String name, String address){   
            this.id = id;   
            this.name = name;   
            this.address = address;   
        }   
  
        public TestObject(){   
  
        }   
  
    }   
  
}