StringBuilder和StringBuffer有哪些区别呢

Author: giantray

README.md

@@ -30,6 +30,7 @@ stackoverflow-Java-top-qa
 > 性能
 
 * [LinkedList、ArrayList各自的使用场景，如何确认应该用哪一个呢？](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/when-to-use-linkedlist-over-arraylist.md)
+* [StringBuilder和StringBuffer有哪些区别呢](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/stringbuilder-and-stringbuffer.md)
 
 
 ### 待翻译问题链接(还剩x问题)
@@ -70,7 +71,6 @@ stackoverflow-Java-top-qa
 - [Comparing Java enum members: == or equals()?](http://stackoverflow.com/questions/1750435/comparing-java-enum-members-or-equals)
 - [Failed to load the JNI shared Library (JDK)](http://stackoverflow.com/questions/7352493/failed-to-load-the-jni-shared-library-jdk)
 - [Does Java support default parameter values?](http://stackoverflow.com/questions/997482/does-java-support-default-parameter-values)
-- [StringBuilder and StringBuffer](http://stackoverflow.com/questions/355089/stringbuilder-and-stringbuffer)
 - [How to concatenate two arrays in Java?](http://stackoverflow.com/questions/80476/how-to-concatenate-two-arrays-in-java)
 - [What's the simplest way to print a Java array?](http://stackoverflow.com/questions/409784/whats-the-simplest-way-to-print-a-java-array)
 - [Why can't I switch on a String?](http://stackoverflow.com/questions/338206/why-cant-i-switch-on-a-string)

contents/stringbuilder-and-stringbuffer.md

@@ -0,0 +1,46 @@
+##StringBuilder和StringBuffer有哪些区别呢
+
+###最主要的区别，StringBuffer的实现使用了synchronized（锁），而StringBuilder没有。
+
+因此，StringBuilder会比StringBuffer快。
+
+如果你
+- 非常非常追求性能（其实这两个都不慢，比直接操作String，要快非常多了）
+- 不需要考虑线程安全问题,
+- JRE是1.5+
+
+可以用StringBuilder,
+反之，请用StringBuffer。
+
+性能测试例子:
+如下这个例子，使用StringBuffer，耗时2241ms,而StringBuilder是753ms
+```java
+public class Main {
+    public static void main(String[] args) {
+        int N = 77777777;
+        long t;
+
+        {
+            StringBuffer sb = new StringBuffer();
+            t = System.currentTimeMillis();
+            for (int i = N; i --> 0 ;) {
+                sb.append("");
+            }
+            System.out.println(System.currentTimeMillis() - t);
+        }
+
+        {
+            StringBuilder sb = new StringBuilder();
+            t = System.currentTimeMillis();
+            for (int i = N; i --> 0 ;) {
+                sb.append("");
+            }
+            System.out.println(System.currentTimeMillis() - t);
+        }
+    }
+}
+```
+
+
+stackoverflow讨论原址
+http://stackoverflow.com/questions/355089/stringbuilder-and-stringbuffer