Setset=map.keySet();
public Set keySet() {
Set ks = keySet;
return (ks != null ? ks : (keySet = new KeySet()));
}
private final class KeySet extends AbstractSet<K> {
public Iterator<K> iterator() {
return newKeyIterator();
}
public int size() {
return size;
}
public boolean contains(Object o) {
return containsKey(o);
}
public boolean remove(Object o) {
return HashMap.this.removeEntryForKey(o) != null;
}
public void clear() {
HashMap.this.clear();
}
}
看HashMap的源码中,keySet()方法,源码就是new了一个keySet也没有执行代码呀,是如何获得map中的key的set集合的?