第十二周作业

1.

public class hellowword {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        String str = "HelloWorld";
        char[] ch = str.toCharArray();
        StringBuffer buffer = new StringBuffer();

        for (int i = str.length() - 1; i >= 0; i--) {
            if ((ch[i] >= 'A') && (ch[i] <= 'Z')) {
                buffer.append(String.valueOf(ch[i]).toLowerCase());
            } else if ((ch[i] >= 'a') && (ch[i] <= 'z')) {
                buffer.append(String.valueOf(ch[i]).toUpperCase());
            }
        }

        System.out.println(buffer.toString());
    }
}

　　2.

import java.util.Random;

public class test {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Random rand = new Random();
        int[] num = new int[5];

        for (int i = 0; i < num.length; i++) {
            num[i] = 20 + rand.nextInt(31);
            System.out.println(num[i]);
        }
    }
}