通过添加/减去相应的值来合并地图

时间:2012-02-18 09:53:48

标签: java map addition subtraction

我一直想知道几天,对我的问题可能是最不凌乱的方法。我有一组10枚枚举类型,例如{ZERO,ONE,TWO,THREE,FIVE,SIX,SEVEN,EIGHT,NINE}我将这些枚举用作地图中的键

Map<MyEnumType, Integer> myMap;

然后我生成100个左右的这些地图,使用相同的键但值不同。将所有这些地图添加到一个地图中的最佳做法是什么?我的意思是将我生成的100张地图的所有值加起来。

2 个答案:

答案 0 :(得分:4)

迭代枚举值,并为每个枚举值迭代映射(反之亦然):

Map<MyEnumType, Integer> sumMap = new EnumMap<MyEnumType, Integer>(MyEnumType.class);
for (MyEnumType e : MyEnumType.values()) {
    int sum = 0;
    for (Map<MyEnumType, Integer> map : maps) {
        sum += map.get(e); // you might want a null check here
    }
    sumMap.put(e, sum);
}

答案 1 :(得分:1)

其他选项是创建特定于用于求和整数的类,而不是覆盖先前的值。以下是匿名类如何完成的示例:

public class MapSummer {

    private final Map<MyEnumType, Integer> sumMap = new HashMap<MyEnumType, Integer>() {
        @Override
        public Integer put(MyEnumType key, Integer value) {
            return super.put(key, get(key) + value);
        }

        @Override
        public Integer get(Object key) {
            return super.get(key) != null ? super.get(key) : 0;
        }
    };

    public Map<MyEnumType, Integer> sum(List<Map<MyEnumType, Integer>> mapList) {
        for (Map<MyEnumType, Integer> map : mapList) {
            sumMap.putAll(map);
        }
        return sumMap;
    }

}

enum MyEnumType {
    ONE, TWO, THREE, FOUR;
}

单元测试:

public class MapSummerTest {

    private final MapSummer summer = new MapSummer();

    @Test
    public void shouldSumValuesInMap() {
        final Map<MyEnumType, Integer> map1 = new HashMap<MyEnumType, Integer>() {{
            put(ONE, 1);
            put(TWO, 2);
        }};

        final Map<MyEnumType, Integer> map2 = new HashMap<MyEnumType, Integer>() {{
            put(TWO, 2);
            put(THREE, 3);
        }};

        final Map<MyEnumType, Integer> sumMap = summer.sum(Arrays.asList(map1, map2));

        assertThat(sumMap.get(ONE), equalTo(1));
        assertThat(sumMap.get(TWO), equalTo(4));
        assertThat(sumMap.get(THREE), equalTo(3));
        assertThat(sumMap.get(FOUR), equalTo(0));
    }
}