String(String original):
String(char[] value):
String(char[] value, int index, int count):

equals(Object obj)://区分大小写
equalsIgnoreCase(String str)://不分大小写
startsWith(String str):
endsWith(String str):

length()://int
charAt(int index):char
indexOf(String str):int
String substring(int start):String
String substring(int start,int end):

char[] toCharArray():
String toLowerCase():
String toUpperCase():

String trim()
String[] split(String str)

StringBuilder()
StringBuilder(str)
capacity()//理论存储能力
length()//实际存储长度

append(任意类型)
reverse()

String(String original):
String(char[] value):
String(char[] value, int index, int count):

equals(Object obj)://区分大小写
equalsIgnoreCase(String str)://不分大小写
startsWith(String str):
endsWith(String str):

length()://int
charAt(int index):char
indexOf(String str):int
String substring(int start):String
String substring(int start,int end):

char[] toCharArray():
String toLowerCase():
String toUpperCase():

String trim()
String[] split(String str)

StringBuilder()
StringBuilder(str)
capacity()//理论存储能力
length()//实际存储长度

append(任意类型)
reverse()