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java - 在方法内部的 if 语句中使用递归时的奇怪行为。爪哇

问题描述

在通过在线课程学习 Java 的同时，我正在尝试使用教程编写的一些代码。有一种方法应该连接“课程”并最终将它们打印出来。我想使用递归而不是循环。

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.
}

当此方法运行时，它会一直提示输入，直到按下“Q”。串联工作正常。然后它留下“if 语句”并且（对我来说很奇怪）它运行最后两行 println 代码的次数与提供的输入一样多。

例如，当我输入三种“课程”然后按“Q”时，输出为：

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

你能告诉我发生了什么吗？

编辑：我已阅读理解递归 [关闭]，但我没有找到任何有关递归如何影响调用堆栈的信息。关于如何使用递归有很多很好的信息，但我仍然没有在那里找到我的问题的答案。

标签： javarecursionmethods

解决方案

问题是您不希望在用户进入课程的情况下打印递归，一个简单的 else 将解决问题

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;
}

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