add java solution for leetcode 191

Author: Zhanganjin0520

README.md

@@ -231,7 +231,7 @@ LeetCode
 |200|[Number of Islands](https://leetcode.com/problems/number-of-islands/)| |Medium|
 |199|[Binary Tree Right Side View](https://leetcode.com/problems/binary-tree-right-side-view/)| |Medium|
 |198|[House Robber](https://leetcode.com/problems/house-robber/)| |Easy|
-|191|[Number of 1 Bits](https://leetcode.com/problems/number-of-1-bits/)| |Easy|
+|191|[Number of 1 Bits](https://leetcode.com/problems/number-of-1-bits/)| [java](./algorithms/numberof1bits/Solution.java) |Easy|
 |190|[Reverse Bits](https://leetcode.com/problems/reverse-bits/)| |Easy|
 |189|[Rotate Array](https://leetcode.com/problems/rotate-array/)| |Easy|
 |188|[Best Time to Buy and Sell Stock IV](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iv/)| |Hard|

algorithms/numberof1bits/Solution.java

@@ -0,0 +1,17 @@
+public class Solution {
+    public int hammingWeight(int n) {
+        int bits = 0;
+        int mask = 1;
+        //32位，循环32次
+        for (int i = 0; i < 32; i++) {
+            //利用 mask 的特性 以及 位元算中的且运算
+            if ((n & mask) != 0) {
+                bits++;
+            }
+            //左移一位
+            mask <<= 1;
+        }
+        return bits;
+    }
+
+}