在方法內部的if語句中使用遞歸時的奇怪行為。 Java的

Question

通過在線課程學習Java時，我正在嘗試使用本教程編寫的一些代碼。 有一種方法可以連接“課程”，最后將它們打印出來。 我想使用遞歸而不是循環。

private String courses = "";
private int tuitionBalance = 0;

public void enroll() {
    System.out.println("Enter course to enroll or \"Q\" to quit.");
    Scanner in = new Scanner(System.in);
    String course = in.nextLine();
    if (!course.equalsIgnoreCase("q")) {
        courses = courses + "\n" + course;
        tuitionBalance = tuitionBalance + costOfCourse;
        enroll();
    }

    System.out.println("Enrolled in: " + courses);
    System.out.println("Tuition balance: " + tuitionBalance);
    return; // even with "return", this method executes multiple times after leaving if statement.
}

當此方法運行時，它將一直提示輸入，直到按下“ Q”。 串聯工作正常。 然后，它留下“ if語句”，並且（對於我來說奇怪的是）它運行了最后兩行println代碼，次數與提供的輸入相同。

例如，當我輸入三種類型的“課程”然后按“ Q”時，輸出為：

Enter course to enroll or "Q" to quit.
History  // My entry
Enter course to enroll or "Q" to quit.
Math  // My entry
Enter course to enroll or "Q" to quit.
Biology  // My entry
Enter course to enroll or "Q" to quit.
q  // My entry
Enrolled in: 
History
Math
Biology
Tuition balance: 1800
Enrolled in: 
History
Math
Biology
Tuition balance: 1800
Enrolled in: 
History
Math
Biology
Tuition balance: 1800
Enrolled in: 
History
Math
Biology
Tuition balance: 1800

Process finished with exit code 0

你能告訴我發生了什么嗎？

編輯：我讀了理解遞歸[關閉] ，但我還沒有找到有關遞歸如何影響調用堆棧的任何信息。 關於如何使用遞歸的信息很多，但是我仍然沒有找到我的問題的答案。

Answer 1

問題是您不希望在用戶進入課程的情況下打印遞歸，簡單的其他方法就可以解決問題

private String courses = "";
private int tuitionBalance = 0;

public void enroll() {
    System.out.println("Enter course to enroll or \"Q\" to quit.");
    Scanner in = new Scanner(System.in);
    String course = in.nextLine();
    if (!course.equalsIgnoreCase("q")) {
        courses = courses + "\n" + course;
        tuitionBalance = tuitionBalance + costOfCourse;
        enroll(); 
    }
    else{//now it would come here only once after user has entered q after which it returns
    System.out.println("Enrolled in: " + courses);
    System.out.println("Tuition balance: " + tuitionBalance);
     }
    return;
}