Determine whether it is a number, a letter, or a Chinese character

1.isDigit/isLetter method

JDK has its own isDigit/isLetter method, which can determine whether a character is a number/letter.

    public static void isNum() {
        String s = ".?abcd123;";
        for (int i=0; i<s.length(); i++) {
            char c = s.charAt(i);
            boolean letter = Character.isLetter(c);
            boolean digit = Character.isDigit(c);
            System.out.println(c + " is letter: " + letter + ", is digit: " + digit);
        }
    }

The output of the above method is

. is letter: false, is digit: false
? is letter: false, is digit: false
a is letter: true, is digit: false
b is letter: true, is digit: false
c is letter: true, is digit: false
d is letter: true, is digit: false
1 is letter: false, is digit: true
2 is letter: false, is digit: true
3 is letter: false, is digit: true
; is letter: false, is digit: false

2.ascii code

The ascii codes corresponding to 0-9 are 48-57, AZ:65-90, az:97-122.
You can use the ascii code value to judge.

    public static void asciimethod() {
        String s = ".?abcd023;";
        boolean flag = false;
        for(int i=0; i<s.length(); i++) {
            char c = s.charAt(i);
            // 0-9:48-57,a-z:97-122,A-Z:65-90
            if (c >= 48 && c <= 57) flag = true;
            System.out.println(c + " is num: " + flag);
            flag = false;
        }
    }

3. Regular match

Regular matching is also a common method for us to process strings.

    public static void remethod() {
        String s1 = "1231";
        Pattern pattern = Pattern.compile("[0-9]*");
        boolean f1 = pattern.matcher(s1).matches();
        System.out.println("s1 is num: " + f1);
        String s2 = "12ab";
        boolean f2 = pattern.matcher(s2).matches();
        System.out.println("s2 is num: " + f2);
    }

4. Determine the use of regular Chinese characters

To determine whether a character is a Chinese character, you can use regular matching.

    public static void checkCharCn() {
        String s1 = "你好";
        String regex = "[\u4e00-\u9fa5]";
        Pattern pattern = Pattern.compile(regex);
        for (int i=0; i<s1.length(); i++) {
            char c = s1.charAt(i);
            boolean flag = pattern.matcher(String.valueOf(c)).matches();
            System.out.println(c + " is CN char: " + flag);
        }
    }

Among them, 4e00-9fa5 represents the unicode encoding range of Chinese characters. For the relationship between unicode encoding and utf-8, utf-16, you can refer to reference 1.

5. Judging Chinese characters UnicodeScript

Starting from JDK1.7, UnicodeScript can also be used to determine whether it is a Chinese character.

    public static boolean isChinese(char c) {
        Character.UnicodeScript sc = Character.UnicodeScript.of(c);
        if (sc == Character.UnicodeScript.HAN) {
            return true;
        }

        return false;
    }

references

1.https://www.cnblogs.com/kingcat/archive/2012/10/16/2726334.html