[Java] HashMap簡易使用方法及如何排序 @ 自由手記

宣告：前面KeyType, 後面ValueType

1 2	`HashMap<String, Integer> hashMap =` `new` `HashMap<String, Integer>();`

放入新元素

1	`hashMap.put(Key,Value);`

得到特定Key的Value：若無此Key回傳null

1	`hashMap.get(Key);`

更新特定Key,Value：以加一為例

1	`hashMap.put(Key, hashMap.get(Key)+1);`

輸出

1

2

3

for(KetType Key: hashMap.keySet()){
    System.out.println(Key, hashMap.get(Key));
}

排序後輸出（以降冪為例)：利用ArrayList

    List<map.entry<String, Integer>> list = new ArrayList<map.entry>(hashMap.entrySet());
        Collections.sort(list,new Comparator<map.entry<String, Integer>>() {
            @Override
            public int compare(Map.Entry<String, Integer> entry1, Map.Entry<String, Integer> entry2) {
                return (entry2.getValue()-entry1.getValue());
            }
        });
        for (Map.Entry<String, Integer> entry:list){
            System.out.println(entry.getKey()+" : "+hashMap.get(entry.getKey()));
        }