Summary of API method

String Class common methods ;
in length();  Returns the length of the current string object ~~ Query length 
char charAt(int index);  Returns the current string object subscript int The character at  index The character at ~~ Find the corresponding character according to the index 
 int indexOf(int ch);  Returns the index of the specified string that first appears in this string ~~ Find the corresponding index according to the characters 
int indexOf(String str,int fromIndex);  Returns the index of the specified string that first appears in this string , Start with the specified index ~~ Find the corresponding index according to the characters （ Section ）
String subString(int beginIndex); Returns the current string from beginIndex The string from the beginning to the end of the string ~~ Intercepting string 
String subString(int beginIndex,int endIndex);  Returns the current string from beginIndex Start to endIndex-1 String ~~ Intercepting string 
boolean equals(Object obj); Compare this string to the specified object ~~ Compare 
bnoolean equalsIgnoreCase(String s); Put this String  And another String Compare , Regardless of case ~~ Compare 
int compareTo(String another-s); Compare two strings in dictionary order ~~ Compare 
String concat(String str); The string str Connect to the tail of the current wear , Returns a new string  ~~ String at connection location 
String replace(char oldCh,char newCh); The character of the string oldCh Replace with string newCh~~ Replace 
String toLowerCase(); Converts uppercase characters in a string to lowercase characters ~~ Replace 
String toUpperCase(); Converts lowercase characters in a string to uppercase characters ~~ Replace 
static String valueOf(type variable); Return variable variable Worth string form ,type It can be a basic type ~~ transformation 
static String valueOf(char[] date,int offset,int count); Returns an array of characters date From the subscript offset At the beginning count A string 
static String valueOf(Object obj); Returns the object obj character string 
String toString(); Returns the current string 
StringBuffer class ( You need to create an object , Call with object ):
in length();  Returns the length of the string in the current buffer ~~ Query length 
char charAt(int index);  Returns the character subscript in the current buffer intex The character at ~~ Find the corresponding character according to the index 
void setcharAt(int index,char ch); Subscript the string in the current cache index The character at changes the character ch Value 
int capacity(); Returns the current cache length 
StringBuffer append(Object obj); take obj.toString() The returned string is added to the end of the current string 
StringBuffer append(type variable); Convert the variable value into a string and add it to the end of the current string ,type It could be an array 、 Strings and various basic types 
StringBuffer insert(int offset,Object obj); take obj.toString() The returned string is inserted into the current character subscript offset It's about 
StringBuffer append(char[]str, type variable); Convert variable values to strings , Insert into the current character array with the subscript offset Location 
String toString(); Convert a variable string to an immutable string 
Collecttions Algorithm class :
addAll(); Add elements 
sort(); Collection sorting 
reverse(); Set in reverse order 
shuffle(); Realize mixed arrangement 
replaceAll(); Realize the replacement of elements 
binarySearch(); Two points search ;
swap(); Exchange elements at specified positions