8种有效方式迭代Java Map中的每个条目

1 iterator + Map.Entry

long i = 0;
Iterator> it = map.entrySet().iterator();
while (it.hasNext()) {
    Map.Entry pair = it.next();
    i += pair.getKey() + pair.getValue();
}
System.out.println(i);

2 foreach + Map.Entry

long i = 0;
for (Map.Entry pair : map.entrySet()) {
    i += pair.getKey() + pair.getValue();
}
System.out.println(i);

3 foreach Java8

final long[] i = {0};
map.forEach((k, v) -> i[0] += k + v);
System.out.println(i[0]);

4 keySet + foreach

long i = 0;
for (Integer key : map.keySet()) {
    i += key + map.get(key);
}
System.out.println(i);

5 keySet + iterator

long i = 0;
Iterator it = map.keySet().iterator();
while (it.hasNext()) {
    Integer key = it.next();
    i += key + map.get(key);
}
System.out.println(i);

6 for + Map.Entry

long i = 0;
for (Iterator> entries = map.entrySet().iterator(); entries.hasNext(); ) {
    Map.Entry entry = entries.next();
    i += entry.getKey() + entry.getValue();
}
System.out.println(i);

7 Java8 Stream Api

System.out.println(map.entrySet().stream().mapToLong(e -> e.getKey() + e.getValue()).sum());

8 Java8 Stream Api parallel

System.out.println(map.entrySet().parallelStream().mapToLong(e -> e.getKey() + e.getValue()).sum());