????13??concat() ?????????????
????14 ??replace() ?滻
????????????????????????????????????????????????г??????????????????滻?????????    ??
????String replace(char original??char replacement)
???????磺String s="Hello".replace('l'??'w');
???????????????????????????滻???????????У???????￡?
????String replace(CharSequence original??CharSequence replacement)
????15??trim() ?????????β????
????16??valueOf() ?????????
????17??toLowerCase() ????Сд
????18??toUpperCase() ??????д
????19??StringBuffer??????
????StringBuffer??????????????????
????StringBuffer()
????StringBuffer(int size)
????StringBuffer(String str)
????StringBuffer(CharSequence chars)
????(1)??length()??capacity()
???????StringBuffer???????????length()?????????????????????????capacity()?????????
????(2)??ensureCapacity() ????????????С
????void ensureCapacity(int capacity)
????(3)??setLength() ??????????????
????void setLength(int len)
????(4)??charAt()??setCharAt()
????char charAt(int where)
????void setCharAt(int where??char ch)
????(5)??getChars()
????void getChars(int sourceStart??int sourceEnd??char target[]??int targetStart)
????(6)??append() ????κ????????????????????????????StringBuffer??????β??
????????int a=42;
????StringBuffer sb=new StringBuffer(40);
????String s=sb.append("a=").append(a).append("!").toString();
????(7)??insert() ?????????
????StringBuffer insert(int index??String str)
????StringBuffer insert(int index??char ch)
????StringBuffer insert(int index??Object obj)
????index??????????????StringBuffer?????е?λ????±?
????(8)??reverse() ???StringBuffer?????е????
????StringBuffer reverse()
????(9)??delete()??deleteCharAt() ??????
????StringBuffer delete(int startIndex??int endIndex)
????StringBuffer deleteCharAt(int loc)
????(10)??replace() ?滻
????StringBuffer replace(int startIndex??int endIndex??String str)
????(11)??substring() ??????
????String substring(int startIndex)
????String substring(int startIndex??int endIndex)