1. StringBuffer
1.1 StringBuffer构造方法
StringBuffer();
StringBuffer(String str);
1.2 添加方法
append(Everything)
insert(int index, Everything)
1.3 查看方法
String toString();
int length();
String substring(int begin);
String substring(int begin, int end);
int indexOf(String str);
int lastIndexOf(String str);
1.4 修改方法
replace(int start, int end, String str);
setCharAt(int index, char ch);
1.5 删除和反序
delete(int start, int end);
deleteCharAt(int index);
reverse();
2. Math数学类
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();