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Commit eec0c32

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StringBuilder和StringBuffer有哪些区别呢
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‎README.md

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> 性能
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* [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)
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* [StringBuilder和StringBuffer有哪些区别呢](https://github.com/giantray/stackoverflow-java-top-qa/blob/master/contents/stringbuilder-and-stringbuffer.md)
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### 待翻译问题链接(还剩x问题)
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- [Comparing Java enum members: == or equals()?](http://stackoverflow.com/questions/1750435/comparing-java-enum-members-or-equals)
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- [Failed to load the JNI shared Library (JDK)](http://stackoverflow.com/questions/7352493/failed-to-load-the-jni-shared-library-jdk)
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- [Does Java support default parameter values?](http://stackoverflow.com/questions/997482/does-java-support-default-parameter-values)
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- [StringBuilder and StringBuffer](http://stackoverflow.com/questions/355089/stringbuilder-and-stringbuffer)
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- [How to concatenate two arrays in Java?](http://stackoverflow.com/questions/80476/how-to-concatenate-two-arrays-in-java)
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- [What's the simplest way to print a Java array?](http://stackoverflow.com/questions/409784/whats-the-simplest-way-to-print-a-java-array)
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- [Why can't I switch on a String?](http://stackoverflow.com/questions/338206/why-cant-i-switch-on-a-string)
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##StringBuilder和StringBuffer有哪些区别呢
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###最主要的区别,StringBuffer的实现使用了synchronized(锁),而StringBuilder没有。
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因此,StringBuilder会比StringBuffer快。
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如果你
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- 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)
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- 不需要考虑线程安全问题,
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- JRE是1.5+
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可以用StringBuilder,
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反之,请用StringBuffer。
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性能测试例子:
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如下这个例子,使用StringBuffer,耗时2241ms,而StringBuilder是753ms
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```java
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public class Main {
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public static void main(String[] args) {
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int N = 77777777;
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long t;
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{
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StringBuffer sb = new StringBuffer();
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t = System.currentTimeMillis();
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for (int i = N; i --> 0 ;) {
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sb.append("");
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}
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System.out.println(System.currentTimeMillis() - t);
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}
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{
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StringBuilder sb = new StringBuilder();
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t = System.currentTimeMillis();
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for (int i = N; i --> 0 ;) {
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sb.append("");
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}
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System.out.println(System.currentTimeMillis() - t);
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}
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}
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}
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```
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stackoverflow讨论原址
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http://stackoverflow.com/questions/355089/stringbuilder-and-stringbuffer

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