📝 Writing docs.

MD/HashMap.md

@@ -22,6 +22,31 @@
 
 get 和 put 类似，也是将传入的 Key 计算出 index ，如果该位置上是一个链表就需要遍历整个链表，通过 `key.equals(k)` 来找到对应的元素。
 
+## 遍历方式
+
+
+```java
+ Iterator<Map.Entry<String, Integer>> entryIterator = map.entrySet().iterator();
+        while (entryIterator.hasNext()) {
+            Map.Entry<String, Integer> next = entryIterator.next();
+            System.out.println("key=" + next.getKey() + " value=" + next.getValue());
+        }
+```
+
+```java
+Iterator<String> iterator = map.keySet().iterator();
+        while (iterator.hasNext()){
+            String key = iterator.next();
+            System.out.println("key=" + key + " value=" + map.get(key));
+
+        }
+```
+
+**强烈建议**使用第一种 EntrySet 进行遍历。
+
+第一种可以把 key value 同时取出，第二种还得需要通过 key 取一次 value，效率较低。
+
+
 ## notice
 
 在并发环境下使用 `HashMap` 容易出现死循环。

MD/collection/HashSet.md

@@ -19,7 +19,7 @@
 
 ## 构造函数
 
-```
+```java
     public HashSet() {
         map = new HashMap<>();
     }

README.md

@@ -15,6 +15,7 @@ Java 知识点，继续完善中。
 - [ArrayList/Vector](https://github.com/crossoverJie/Java-Interview/blob/master/MD/ArrayList.md)
 - [LinkedList](https://github.com/crossoverJie/Java-Interview/blob/master/MD/LinkedList.md)
 - [HashMap](https://github.com/crossoverJie/Java-Interview/blob/master/MD/HashMap.md)
+- [HashSet](https://github.com/crossoverJie/Java-Interview/blob/master/MD/HashMap.md)
 - [LinkedHashMap](https://github.com/crossoverJie/Java-Interview/blob/master/MD/collection/LinkedHashMap.md)
 
 ### Java 多线程
@@ -67,7 +68,7 @@ Java 知识点，继续完善中。
 - [是否为快乐数字](https://github.com/crossoverJie/Java-Interview/blob/master/src/main/java/com/crossoverjie/algorithm/HappyNum.java#L38-L55)
 - [链表是否有环](https://github.com/crossoverJie/Java-Interview/blob/master/src/main/java/com/crossoverjie/algorithm/LinkLoop.java#L32-L59)
 - [从一个数组中返回两个值相加等于目标值的下标](https://github.com/crossoverJie/Java-Interview/blob/master/src/main/java/com/crossoverjie/algorithm/TwoSum.java#L38-L59)
-- [一致 Hash 算法](https://github.com/crossoverJie/Java-Interview/blob/master/MD/Consistent-Hash.md)
+- [一致性 Hash 算法](https://github.com/crossoverJie/Java-Interview/blob/master/MD/Consistent-Hash.md)
 - [限流算法](https://github.com/crossoverJie/Java-Interview/blob/master/MD/Limiting.md)
 - [三种方式反向打印单向链表](https://github.com/crossoverJie/Java-Interview/blob/master/src/main/java/com/crossoverjie/algorithm/ReverseNode.java)
 - [合并两个排好序的链表](https://github.com/crossoverJie/Java-Interview/blob/master/src/main/java/com/crossoverjie/algorithm/MergeTwoSortedLists.java)

src/main/java/com/crossoverjie/basic/HashMapTest.java

@@ -0,0 +1,37 @@
+package com.crossoverjie.basic;
+
+import java.security.Key;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.Map;
+
+/**
+ * Function:
+ *
+ * @author crossoverJie
+ *         Date: 05/05/2018 12:42
+ * @since JDK 1.8
+ */
+public class HashMapTest {
+    public static void main(String[] args) {
+        Map<String, Integer> map = new HashMap<>(16);
+        map.put("1", 1);
+        map.put("2", 2);
+        map.put("3", 3);
+        map.put("4", 4);
+
+        Iterator<Map.Entry<String, Integer>> entryIterator = map.entrySet().iterator();
+        while (entryIterator.hasNext()) {
+            Map.Entry<String, Integer> next = entryIterator.next();
+            System.out.println("key=" + next.getKey() + " value=" + next.getValue());
+        }
+        System.out.println("=============");
+
+        Iterator<String> iterator = map.keySet().iterator();
+        while (iterator.hasNext()){
+            String key = iterator.next();
+            System.out.println("key=" + key + " value=" + map.get(key));
+
+        }
+    }
+}