Chapter 10 Exercise 24, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

10.24 (Implement the Character class)
The Character class is provided in the Java library.
Provide your own implementation for this class.
Name the new class MyCharacter.

public class MyCharacter {

    private char ch;

    public MyCharacter(char ch) {
        this.ch = ch;
    }

    public static boolean isDigit(char ch) {
        return ch <= '9' && ch >= '0';
    }

    public static boolean isLowerCase(char ch) {

        return (ch <= 'z' && ch >= 'a');
    }

    public static boolean isUpperCase(char ch) {
        return (ch <= 'Z' && ch >= 'A');
    }

    public static boolean isLetter(char ch) {
        return (ch <= 'z' && ch >= 'a') ||
                (ch <= 'Z' && ch >= 'A');
    }

    public static boolean isLetterOrDigit(char ch) {
        return isLetter(ch) || isDigit(ch);
    }

    public static char toUpperCase(char ch) {
        if (isLowerCase(ch)) {
            return (char) (ch - 'a' + 'A');
        } else {
            return ch;
        }
    }

    public static char toLowerCase(char ch) {
        if (isUpperCase(ch)) {
            return (char) (ch - 'A' + 'a');
        } else {
            return ch;
        }
    }

    public boolean isDigit() {
        return isDigit(ch);
    }

    public boolean isLetter() {
        return isLetter(ch);
    }

    public char getChar() {
        return ch;
    }

    public int compareTo(MyCharacter ch) {
        return this.ch - ch.getChar();
    }

    public boolean equals(MyCharacter ch) {
        return this.ch == ch.getChar();
    }

}

public class Exercise_24 {
    public static void main(String[] args) {
        MyCharacter ch = new MyCharacter('L');
        System.out.println("ch = " + ch.getChar());
        System.out.println("Is a letter: " + ch.isLetter());
        System.out.println("Is a digit: " + ch.isDigit());
        System.out.println("L == L ?" + ch.equals(new MyCharacter('L')));
    }
}