//Character常用方法
//注意是静态方法
static boolean isLetter(char ch);
static boolean isLetter(int codePoint);
static boolean isDigit(char ch);
static boolean isDigit(int codePoint);
static boolean isLetterOrDigit(char ch);
static boolean isLetterOrDigit(int codePoint);
static char toLowerCase(char ch); //大写字母变小写
