下面是兩個具有兩個不同功能的遞歸代碼。[1]我使用遞歸代碼檢查回文是這樣的：import java.util.Scanner;public class CheckPalindromeRecursion {public static boolean recursion(String pal) {    if (pal.length() == 0 || pal.length() == 1) {        return true;    } else if (pal.charAt(0) == pal.charAt(pal.length() - 1)) {        return recursion(pal.substring(1, pal.length() - 1));    }    return false;}public static void main(String[] args) {    System.out.println("Enter the String for check:");    Scanner scan = new Scanner(System.in);    String str = scan.nextLine();    if(recursion(str))        System.out.println(str + " is a palindrome");    else        System.out.println(str + " is not a palindrome");    scan.close();}}[2]我使用遞歸代碼反轉一個數字是這樣的：import java.util.Scanner;public class ReverseNumberRecursion {public static void reverse(int numb) {    if (numb < 10) {        System.out.print(numb);        return;    } else {        System.out.print(numb % 10);        reverse(numb/10);    }}public static void main(String[] args) {    System.out.print("The number you want to reverse is: ");    Scanner in = new Scanner(System.in);    int numb = in.nextInt();    in.close();    System.out.print("The reversed number is: ");    reverse(numb);}}為什么我必須在 - [1]:中使用返回，但在 - [2]:中不需要使用返回？ return recursion(pal.substring(1, pal.length() - 1)); reverse(numb/10);