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

equals(Object obj):
equalsIgnoreCase(String str):
startsWith(String str):
endsWith(String str):

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

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

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

StringBuilder()
StringBuilder(str)
capacity()
length()

append(任意类型)
reverse()

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

equals(Object obj):
equalsIgnoreCase(String str):
startsWith(String str):
endsWith(String str):

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

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

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

StringBuilder()
StringBuilder(str)
capacity()
length()

append(任意类型)
reverse()