Java8 HashMap遍历方式性能探讨

Map<String, String> map = new HashMap<String, String>();
        int num = 5000000;
        String key, value;
        // 存放500万条数据
        for (int i = 1; i <= num; i++) {
            key = "" + i;
            value = "value";
            map.put(key, value);

     }

Map map=new HashMap();
Iterator it=map.keySet().iterator();
Object key;
Object value;
while(it.hasNext()){
key=it.next();
value=map.get(key);
System.out.println(key+":"+value);
}

Map map=new HashMap();
Iterator it=map.entrySet().iterator();
Object key;
Object value;
while(it.hasNext()){
Map.Entry entry = (Map.Entry)it.next();
key=entry.getKey();
value=entry.getValue();
System.out.println(key+"="+value);
}

final class KeyIterator extends HashIterator
        implements Iterator<K> {
        public final K next() { return nextNode().key; }
    }

final class EntryIterator extends HashIterator
        implements Iterator<Map.Entry<K,V>> {
        public final Map.Entry<K,V> next() { return nextNode(); }
    }

for (String key1 : map.keySet()) {
            value = map.get(key1);
}

for (Entry<String, String> entry1 : map.entrySet()) {
	key = entry1.getKey();
	value = entry1.getValue();
}

default void forEach(BiConsumer<? super K, ? super V> action) {
        Objects.requireNonNull(action);
        for (Map.Entry<K, V> entry : entrySet()) {
            K k;
            V v;
            try {
                k = entry.getKey();
                v = entry.getValue();
            } catch(IllegalStateException ise) {
                // this usually means the entry is no longer in the map.
                throw new ConcurrentModificationException(ise);
            }
            action.accept(k, v);
        }
    }

Map<String, Integer> items = new HashMap<>();
items.put("A", 10);
items.put("B", 20);
items.put("C", 30);
items.put("D", 40);
items.put("E", 50);
items.put("F", 60);
 
items.forEach((k,v)->System.out.println("Item : " + k + " Count : " + v));
 
items.forEach((k,v)->{
    System.out.println("Item : " + k + " Count : " + v);
    if("E".equals(k)){
        System.out.println("Hello E");
    }
});