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时间:2019-06-16
《比较String和StringBuffer》由会员上传分享,免费在线阅读,更多相关内容在教育资源-天天文库。
1、相信大家看到过很多比较String和StringBuffer区别的文章,也明白这两者的区别,然而自从Java5.0发布以后,我们的比较列表上将多出一个对象了,这就是StringBuilder类。String类是不可变类,任何对String的改变都会引发新的String对象的生成;而StringBuffer则是可变类,任何对它所指代的字符串的改变都不会产生新的对象,可变和不可变类这一对对象已经齐全了,那么为什么还要引入新的StringBuilder类干吗?相信大家都有此疑问,我也如此。下面,我们就来看看引入该类的原因。为什么会出现那么多比较St
2、ring和StringBuffer的文章?原因在于当改变字符串内容时,采用StringBuffer能获得更好的性能。既然是为了获得更好的性能,那么采用StringBuffer能够获得最好的性能吗?答案是NO!为什么?如果你读过《ThinkinJava》,而且对里面描述HashTable和HashMap区别的那部分章节比较熟悉的话,你一定也明白了原因所在。对,就是支持线程同步保证线程安全而导致性能下降的问题。HashTable是线程安全的,很多方法都是synchronized方法,而HashMap不是线程安全的,但其在单线程程序中的性能比Has
3、hTable要高。StringBuffer和StringBuilder类的区别也在于此,新引入的StringBuilder类不是线程安全的,但其在单线程中的性能比StringBuffer高。如果你对此不太相信,可以试试下面的例子:packagecom.hct.test;importjava.util.ArrayList;importjava.util.Iterator;importjava.util.List;/***@author:chengtai.he*@created:2009-12-9上午09:59:57*/publicclassSt
4、ringBuilderTester{privatestaticfinalStringbase="basestring.";privatestaticfinalintcount=2000000;publicstaticvoidstringTest(){longbegin,end;begin=System.currentTimeMillis();Stringtest=newString(base);for(inti=0;i5、;System.out.println((end-begin)+"millishaselapsedwhenusedString.");}publicstaticvoidstringBufferTest(){longbegin,end;begin=System.currentTimeMillis();StringBuffertest=newStringBuffer(base);for(inti=0;i6、m.out.println((end-begin)+"millishaselapsedwhenusedStringBuffer.");}publicstaticvoidstringBuilderTest(){longbegin,end;begin=System.currentTimeMillis();StringBuildertest=newStringBuilder(base);for(inti=0;i7、stem.out.println((end-begin)+"millishaselapsedwhenusedStringBuilder.");}publicstaticStringappendItemsToStringBuiler(Listlist){StringBuilderb=newStringBuilder();for(Iteratori=list.iterator();i.hasNext();){b.append(i.next()).append("");}returnb.toString();}publicstaticvoidadd8、ToStringBuilder(){Listlist=newArrayList();list.add("I");list.add("play");list.add(
5、;System.out.println((end-begin)+"millishaselapsedwhenusedString.");}publicstaticvoidstringBufferTest(){longbegin,end;begin=System.currentTimeMillis();StringBuffertest=newStringBuffer(base);for(inti=0;i6、m.out.println((end-begin)+"millishaselapsedwhenusedStringBuffer.");}publicstaticvoidstringBuilderTest(){longbegin,end;begin=System.currentTimeMillis();StringBuildertest=newStringBuilder(base);for(inti=0;i7、stem.out.println((end-begin)+"millishaselapsedwhenusedStringBuilder.");}publicstaticStringappendItemsToStringBuiler(Listlist){StringBuilderb=newStringBuilder();for(Iteratori=list.iterator();i.hasNext();){b.append(i.next()).append("");}returnb.toString();}publicstaticvoidadd8、ToStringBuilder(){Listlist=newArrayList();list.add("I");list.add("play");list.add(
6、m.out.println((end-begin)+"millishaselapsedwhenusedStringBuffer.");}publicstaticvoidstringBuilderTest(){longbegin,end;begin=System.currentTimeMillis();StringBuildertest=newStringBuilder(base);for(inti=0;i7、stem.out.println((end-begin)+"millishaselapsedwhenusedStringBuilder.");}publicstaticStringappendItemsToStringBuiler(Listlist){StringBuilderb=newStringBuilder();for(Iteratori=list.iterator();i.hasNext();){b.append(i.next()).append("");}returnb.toString();}publicstaticvoidadd8、ToStringBuilder(){Listlist=newArrayList();list.add("I");list.add("play");list.add(
7、stem.out.println((end-begin)+"millishaselapsedwhenusedStringBuilder.");}publicstaticStringappendItemsToStringBuiler(Listlist){StringBuilderb=newStringBuilder();for(Iteratori=list.iterator();i.hasNext();){b.append(i.next()).append("");}returnb.toString();}publicstaticvoidadd
8、ToStringBuilder(){Listlist=newArrayList();list.add("I");list.add("play");list.add(
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