????????????java??string???ЩС??????????????????????????????á???????????????????а??????????????string?????????????????????????????????
????string?????????????????????????????????д???????????????????????????C???????java?У?jdk??????????????????????????????????????String ??StringBuffer ?? StringBuilder .?????????????????????????????????????????????
??????????????String??
????JDK??????? “Strings are constant; their values cannot be changed after they are created”????String??????????????????????????????????????????????????????????????????????????????????????????????д??
???????????????????????????????????String????

???????????????????????java?????????й?????????????string???????????????????????????????????????????????????е?????????У????????????????????????????????С??????????????????int??????????????????????
???????????????????????????????鳣?????????????????“string”??????????????????е????????????str1??????λ?á?
???????????????????????????new??????????java????????java??new??????????У?????????????????????????????????????????new??????????????????????????????????????????????
????д???С????
????Java?е?String???????
????String str1 = "string";
????String str4 = "string";
????String str2 = new String("string");
????String str3 = new String("string");
????/*????????????????????????????*/
????System.out.println(str1 == str4);
????System.out.println(str2 == str3);
????System.out.println(str3 == str1);
????str3 = str3.intern(); //??????????????
????System.out.println(str3 == str1);
????Java?е?String???????
????????????н????
????true //???????????????????????????????????????е?????????
????false //?????????new??????????μ????
????false // ????? ???==??????????????????????
????true //???????intern?????????????????????????????????е????????????????????????str3?????????string?????????????????У???????????д??????string??????????????str3?????????str1??????
????????????????string???????????????????????????????????????????string?????????????str1 + "some"??????????????ζ?string??????????????????μ????
????????????????????????????????????Ч????????????????????????????????????????????μ???????????????????????????????
????Java?е?String???????
????long start = System.currentTimeMillis();
????for(int i = 0; i < 50000; i++)
????{
????str1+= " ";
????}
????long end = System.currentTimeMillis();
????System.out.println("the run time is "+(end -start)+" ms");

???????????????н????the run time is 3538 ms ???????????????????????????0?????????????????????????????????JDK??ν?????????
?????????????????StringBuffer??
????StringBuffer??????????????????????????????????????????????????????????????????仯????????????????????????????????append????string??concat???????????insert???????????????????????????????????API??
????Java?е?String???????
????StringBuilder sb = new StringBuilder("string builder");
????StringBuffer sf = new StringBuffer("string buffer");
????long start = System.currentTimeMillis();
????for(int i = 0; i < 50000; i++)
????{
????//str1+= " ";
????sb.append(" ");
????}
????long end = System.currentTimeMillis();
????System.out.println("the run time is "+(end -start)+" ms");
????Java?е?String???????
??????????￡????????8ms??????Ч???
??????????????????StringBuilder???????????????????????????????????jdk 1.5?汾?????????μ???????StringBuffer?????????????????????￡?????????????????????????????????Ч???????StringBuilder??StringBuffer???????????汾????????????????????????????????????????????????????????????????
??????????????jdk?????????StringBuffer??????????????????????syncronized
????Java?е?String???????
??????????????????????????????????????????????????????????????????????????????????????????ū??API???????????????????????????Щ???????????????????????????????????????????