Java：1.将一个英文字符串中大写字符和小写字符分开显示。 2.统计一个英文字符串中各个字母出现的次数。需要源码

1. 代码实现如下：

public class SeparateChar {
    public static void main(String[] args) {
        String str = "This is a test String";
        String upper = "";
        String lower = "";

        for (int i = 0; i < str.length(); i++) {
            char c = str.charAt(i);
            if (Character.isUpperCase(c)) {
                upper += c + " ";
            }
            else if (Character.isLowerCase(c)) {
                lower += c + " ";
            }
        }

        System.out.println("Uppercase letters: " + upper);
        System.out.println("Lowercase letters: " + lower);
    }
}

2. 代码实现如下：

public class CountLetters {
    public static void main(String[] args) {
        String str = "This is a test String";
        int[] count = new int[26];

        for (int i = 0; i < str.length(); i++) {
            char c = str.charAt(i);
            if (Character.isLetter(c)) {
                count[Character.toLowerCase(c) - 'a']++;
            }
        }

        for (int i = 0; i < 26; i++) {
            if (count[i] != 0) {
                System.out.println((char)('a' + i) + ": " + count[i]);
            }
        }
    }
}