求教!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[Java] 纯文本查看 复制代码

import java.util.Scanner;

public class Test {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner sc = new Scanner(System.in);
		System.out.println("请输入一个字符串：");
		String str = sc.nextLine();
		char[] arr = new char[str.length()];
		for (int i = 0; i < str.length(); i++) {
			arr[i] = str.charAt(i);
		}
		for (int i = 0; i < arr.length; i++) {
			if (arr[i] >= 'A' && arr[i] <= 'Z') {
				arr[i] = (char) (arr[i] + 32);
			}
		}
		if (arr[0] != arr[arr.length - 1]) {
			char temp = arr[0];
			arr[0] = arr[arr.length - 1];
			arr[arr.length - 1] = temp;
		}
		for (int i = 0; i < arr.length; i += 2) {
			arr[i] = '~';
		}
		for (int i = 0; i < arr.length; i++) {
			System.out.print(arr[i] + ", ");
		}
	}
}

这个题目貌似是homework题目