1. StringBuffer
1.1 StringBuffer constructor
StringBuffer();
StringBuffer(String str);
1.2 Add Method
append(Everything)
insert(int index, Everything)
1.3 Methods View
String toString();
int length();
String substring(int begin);
String substring(int begin, int end);
int indexOf(String str);
int lastIndexOf(String str);
1.4 modification method
replace(int start, int end, String str);
setCharAt(int index, char ch);
1.5 Delete and reverse order
delete(int start, int end);
deleteCharAt(int index);
reverse();
2. Math math class
public static double abs(double a);
public static double ceil(double a);
public static double floor(double a);
public static double round(double a);
public static double random();