遍历/打印HashMap和HashSet

总结一下：
针对遍历
就是用for each或者是迭代器
针对打印：(管他是怎么搞 只要打出来能看懂就行)
Hashmap: System.out.println();即可 会自动调用toString()
hashset:直接System.out.println()即可 会自动调用toString()

遍历HashSet:

1. 用迭代器

Set<String> set = new HashSet<String>();  
Iterator<String> it = set.iterator();  //key point 1
while (it.hasNext()) {   //key point 2
  String str = it.next();  //key point 3
}  

2. 用for each

for (Integer num: set) {
}

遍历HashMap:
1.用迭代器

		Iterator<Map.Entry<Integer, Integer>> entries = map.entrySet().iterator();
		while (entries.hasNext()) {
			Map.Entry<Integer, Integer> entry = entries.next();
			System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());
		}

2.用for each遍历
1.遍历键值对
.entrySet()

 for(Map.Entry<Integer, Integer> entry: indegree.entrySet()) {
        if(entry.getValue() == 0) queue.offer(entry.getKey());
}

2. 按照键遍历
   keySet()

for (Integer key : map.keySet()) {
	System.out.println("Key = " + key);
}

3. 按照值遍历
   values()

for (Integer value : map.values()) {
	System.out.println("Value = " + value);
}