类、对象和方法在 Java 中的帮助答案

【问题标题】：Classes, Objects, and Methods help in Java类、对象和方法在 Java 中的帮助
【发布时间】：2015-04-14 03:12:27
【问题描述】：

NetBeans 不允许我运行我的程序，因为公共类 HotelManagement 和公共类 Room 存在问题。谁能帮我解决这个问题，这样我的程序才能顺利运行。谢谢

public class HotelManagement {

    public static void main(String[] args) {
        Room room1 = new Room(3348, 80, "Single Bed"); 
        Room room2 = new Room(3347, 90, "Double Bed"); 
        Room room3 = new Room(3346, 140, "Suite");
        room1.Book(); 
        room2.printRoomInfo(); 
        room3.setRate(180); 
        room1.Release(); 
        room1.printRoomInfo(); 
        room3.printRoomInfo();
    }

    }



    public class Room {


    private final int number;
    private final String type;
    private int rate;
    private boolean isBooked;


    public Room(int number, int rate, String type) {

        this.number = number;
        this.type = type;
        this.rate = rate;
        this.isBooked = false; 
    }


    public void Book() {
        System.out.println("Room " + this.number + " has successfully been booked.");
        this.isBooked = true;
    } 

    // This method "releases" the booking on the room by setting the instance variable isBooked to false
    public void Release() {
        System.out.println("Room " + this.number + " has successfully been released.");
        this.isBooked = false;
    }

    // Print basic info about the current Room objects state 
    public void printRoomInfo() {
        String state; 
        if (this.isBooked == true) { 
            state = "Unavailable"; 
        }

        else { 
            state = "Available";
        }

        System.out.println("Room " + this.number + " is a " + this.type + ". Rate is: " + this.rate + "$ per night. " + state + ".");

    }


    public void setRate(int newRate) {
        this.rate = newRate;
    }
    }

【问题讨论】：

您的程序对我来说运行良好，您是否将所有代码放在一个文件中？
是的，每个文件都有一个顶级类。
@RobertMoskal 您在一个文件中只能有一个“公共”类。因此，您应该将除“HotelManagement”以外的所有课程设为非公开课程或遵循以下答案。

标签： java class object methods

【解决方案1】：

如果你想把两个类放到一个文件中，你需要：

在 HotelManagement 类中移动 Room 类声明
使其成为静态的，例如public static class Room {

所以，最终的结构是这样的：

public class HotelManagement {
    public static void main(String[] args) {
...
    }

    public static class Room {
....
    }
}

【讨论】：

【解决方案2】：

您只能在 .java 文件中拥有一个公共类，该类将是具有您的公共静态 void main 的类。同一文件中的其他类不能公开。

public class HotelManagement {

    public static void main(String[] args) {
        Room room1 = new Room(3348, 80, "Single Bed"); 
        Room room2 = new Room(3347, 90, "Double Bed"); 
        Room room3 = new Room(3346, 140, "Suite");
        room1.Book(); 
        room2.printRoomInfo(); 
        room3.setRate(180); 
        room1.Release(); 
        room1.printRoomInfo(); 
        room3.printRoomInfo();
    }

    }



     class Room {


    private final int number;
    private final String type;
    private int rate;
    private boolean isBooked;


    public Room(int number, int rate, String type) {

        this.number = number;
        this.type = type;
        this.rate = rate;
        this.isBooked = false; 
    }


    public void Book() {
        System.out.println("Room " + this.number + " has successfully been booked.");
        this.isBooked = true;
    } 

    // This method "releases" the booking on the room by setting the instance variable isBooked to false
    public void Release() {
        System.out.println("Room " + this.number + " has successfully been released.");
        this.isBooked = false;
    }

    // Print basic info about the current Room objects state 
    public void printRoomInfo() {
        String state; 
        if (this.isBooked == true) { 
            state = "Unavailable"; 
        }

        else { 
            state = "Available";
        }

        System.out.println("Room " + this.number + " is a " + this.type + ". Rate is: " + this.rate + "$ per night. " + state + ".");

    }


    public void setRate(int newRate) {
        this.rate = newRate;
    }
    }

【讨论】：

【解决方案3】：

每个源文件只能有一个公共类。所以要让你的代码工作，你需要做一件事

将每个公共类放在一个单独的源文件中。无论包是什么，都可以从任何地方访问公共类。
删除public 类Room 的访问修饰符

另一种方法是将Room 类设为静态并将其放入HotelManagement 类中。但我建议您在非常擅长基本概念的情况下学习 Java 中的静态嵌套类和内部类等高级概念。

【讨论】：