将一个List转变为一个Map,并对这样的map进行遍历

将一个List转变为一个Map<Key,List>

这种场景在平常工作中，有很多地方都会用到。这里自己总结一下：

 

 

 

package com.amuse.oneself.test;

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(){

        }

    }

}

 

输出为：

1  :  

<--name1--address1--><--name2--address2--><--name3--address3-->

2  :  

<--name1--address1--><--name2--address2--><--name3--address3-->