JAVA中HashMap（哈希表）的使用(List)方法

来源：中国IT实验室作者：佚名出处：巧巧读书 2008-06-13 进入讨论组

关键词：
java

当hashMap的key是多个字段，且想得到多个value时，可能将key和 value分别做成List
　　

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import java.util.Map;

//inquiry result
List fromDetailList = instHdDao.retrieveInstInfoByView(sysOwnerCd, fromCd, instruct);

    // Initial Value
    Integer dtTotalTruck = 0;
    Integer dtTotalQuantity = 0;

Map hm = new HashMap();

    Iterator it = fromDetailList.iterator();
    while(it.hasNext()){
        MeInstHd meInstHd = (MeInstHd)it.next();

        List arr1 = new ArrayList();
        List arr2 = new ArrayList();
        List arr3 = new ArrayList();

String carrierCd = meInstHd.getCarrCd().trim();

arr1.add(carrierCd); // put keyValue to Arr1

        if(hm.containsKey(arr1)){
            // carrierCd is exist in hm
            arr3 = (ArrayList)hm.get(arr1); // 通过Key arr1取得arr1的Value arr2.List arr3中有２列值，他们分别是dtTotalQuantity 和dtTotalTruck

            dtTotalQuantity = (Integer)arr3.get(0) ;
            dtTotalQuantity += meInstHd.sumInstructQty();
            dtTotalTruck = (Integer)arr3.get(1) ;
            dtTotalTruck += 1;

arr2.add(dtTotalQuantity);
arr2.add(dtTotalTruck);

            hm.put(arr1, arr2); // creat hashMap hm.
        }
        else{
            // carrierCd is not exist in hm
            arr2.add(meInstHd.sumInstructQty()); //put value to arr2
            arr2.add(1); // dtTotalTruck initial value is "1"

            hm.put(arr1,arr2); // 其中arr1是key,arr2是value，可以通过get(arr1)来取得其value
        }
    }