java8 map 转 map

import java.util.HashMap;
import java.util.Map;

public class MapConversionExample {
    public static void main(String[] args) {
        Map<String, Integer> originalMap = new HashMap<>();
        originalMap.put("one", 1);
        originalMap.put("two", 2);
        originalMap.put("three", 3);

        Map<Integer, String> reversedMap = originalMap.entrySet().stream()
            .collect(HashMap::new, (m, e) -> m.put(e.getValue(), e.getKey()), HashMap::putAll);

        System.out.println(reversedMap); // 输出: {1=one, 2=two, 3=three}
    }
}

Map<String, Integer> filteredMap = originalMap.entrySet().stream()
    .filter(entry -> entry.getValue() > 1)
    .collect(HashMap::new, (m, e) -> m.put(e.getKey(), e.getValue()), HashMap::putAll);

System.out.println(filteredMap); // 输出: {two=2, three=3}

Map<String, Integer> map1 = new HashMap<>();
map1.put("a", 1);
map1.put("b", 2);

Map<String, Integer> map2 = new HashMap<>();
map2.put("b", 3); // 注意这里有一个重复的键
map2.put("c", 4);

Map<String, Integer> combinedMap = new HashMap<>(map1);
combinedMap.putAll(map2);

System.out.println(combinedMap); // 输出: {a=1, b=3, c=4} 注意键"b"的值被覆盖了

Map<String, Integer> safeMap = originalMap.entrySet().stream()
    .filter(entry -> entry.getKey() != null && entry.getValue() != null)
    .collect(HashMap::new, (m, e) -> m.put(e.getKey(), e.getValue()), HashMap::putAll);