Java API ——Character类

public class CharacterDemo02 {
    public static void main(String[] args) {
        // public static boolean isUpperCase(char ch):判断给定的字符是否是大写字符
        System.out.println("isUpperCase:" + Character.isUpperCase(‘A‘)); //isUpperCase:true
        System.out.println("isUpperCase:" + Character.isUpperCase(‘a‘)); //isUpperCase:false
        System.out.println("isUpperCase:" + Character.isUpperCase(‘0‘)); //isUpperCase:false
        System.out.println("-----------------------------------------");
        // public static boolean isLowerCase(char ch):判断给定的字符是否是小写字符
        System.out.println("isLowerCase:" + Character.isLowerCase(‘A‘)); //isLowerCase:false
        System.out.println("isLowerCase:" + Character.isLowerCase(‘a‘)); //isLowerCase:true
        System.out.println("isLowerCase:" + Character.isLowerCase(‘0‘)); //isLowerCase:false
        System.out.println("-----------------------------------------");
        // public static boolean isDigit(char ch):判断给定的字符是否是数字字符
        System.out.println("isDigit:" + Character.isDigit(‘A‘)); //isDigit:false
        System.out.println("isDigit:" + Character.isDigit(‘a‘)); //isDigit:false
        System.out.println("isDigit:" + Character.isDigit(‘0‘)); //isDigit:true
        System.out.println("-----------------------------------------");
        // public static char toUpperCase(char ch):把给定的字符转换为大写字符
        System.out.println("toUpperCase:" + Character.toUpperCase(‘A‘)); //toUpperCase:A
        System.out.println("toUpperCase:" + Character.toUpperCase(‘a‘)); //toUpperCase:A
        System.out.println("-----------------------------------------");
        // public static char toLowerCase(char ch):把给定的字符转换为小写字符
        System.out.println("toLowerCase:" + Character.toLowerCase(‘A‘)); //toLowerCase:a
        System.out.println("toLowerCase:" + Character.toLowerCase(‘a‘)); //toLowerCase:a
    }
}

public class CharacterDemo03 {
    public static void main(String[] args) {
        // 定义三个统计变量。
        int bigCount = 0;
        int smallCount = 0;
        int numberCount = 0;
        System.out.println("请输入一个字符串：");
        Scanner sc = new Scanner(System.in);
        String line = sc.nextLine();
        char[] ch = line.toCharArray();
        for(int i = 0; i < ch.length; i++){
            if (Character.isUpperCase(ch[i]))
                bigCount++;
            else if(Character.isLowerCase(ch[i]))
                smallCount++;
            else if(Character.isDigit(ch[i]))
                numberCount++;
        }
        // 输出结果即可
        System.out.println("大写字母：" + bigCount + "个");
        System.out.println("小写字母：" + smallCount + "个");
        System.out.println("数字字符：" + numberCount + "个");
    }
}