无限循环在程序中无法正常工作答案

【问题标题】：Infinite loop not working properly in program无限循环在程序中无法正常工作
【发布时间】：2016-05-09 09:44:22
【问题描述】：

这个程序使用一个二维数组来记录开放和预订的房间。程序在开始和每次改变数组之后都会显示二维数组。索引值代表房间号并针对开放房间显示。预定房间显示预定房间的人的姓名。程序将继续运行，直到用户输入“Q”。

对我来说一切似乎都很好，除了在 main 方法中执行一次循环后，即使用户没有输入“Q”，程序也会停止运行。我也试过用 while(true) 来做，但它仍然不起作用。我真的希望有人可以帮助我。

public static void main (String [] args)
{
    Scanner kb = new Scanner (in);
    out.print("Enter row size: ");
    int row = kb.nextInt();
    out.print("Enter column size: ");
    int col = kb.nextInt();
    kb.nextLine();
    String [][]rooms = roomInIt(row, col);
    printMatrix(rooms);
    String a="";


    for(;;)
    {
        out.print("Would you like to reserve or release a room? Type Q to exit ");
        a = kb.nextLine();

        if (a.equalsIgnoreCase("reserve"))
        {
            out.print("How many rooms would you like to reserve? ");
            int num = kb.nextInt();
            reserveRooms(rooms, num);
        }
        else if (a.equalsIgnoreCase("release"))
        {
            out.print("How many rooms would you like to release? ");
            int x = kb.nextInt();
            releaseRooms(rooms, x);
        }
        else if (a.equalsIgnoreCase("Q"));
            break;
    }
}

public static void printMatrix(String[][]rooms)
{

    for(int r=0; r<rooms.length; r++)
        {
            for (int c=0; c<rooms[r].length; c++)
                out.print("["+r+","+c+"] "+rooms[r][c]+"\t");
            out.println();
        }
}

public static String[][] roomInIt(int row, int col)
{
    String [][]rooms = new String [row][col];
    for(int r=0; r<rooms.length; r++)
        for (int c=0; c<rooms[r].length; c++)
            rooms[r][c]="open";
    return rooms;
}

public static void reserveRooms(String [][]room, int num)
{

    Scanner kb = new Scanner(in);
    for(int i=0; i<num; i++)
    {   
        out.print("Enter name: ");
        String name = kb.nextLine();
        out.print("Enter the room number (row and column separated by a space) ");
        int r=kb.nextInt();
        int c=kb.nextInt();
        kb.nextLine();
        while (r<0 || r>room.length || c<0 || c>room[r].length || !room[r][c].equals("open"))
        {
            out.print("Invalid room number. Enter another room number (row and column separated by a space) ");
            r=kb.nextInt();
            c=kb.nextInt();
            kb.nextLine();
        }
        room[r][c] = name;
    }
    printMatrix(room);
}

public static void releaseRooms(String [][]room, int x)
{
    int r, c;
    Scanner kb = new Scanner(in);
    for(int i=0; i<x; i++)
    {   
        out.print("Enter name: ");
        String name = kb.nextLine();
        out.print("Enter the room number (row and column separated by a space) ");
        r=kb.nextInt();
        c=kb.nextInt();
        kb.nextLine();
        while(r<0 || r>room.length || c<0 || c>room[r].length)
        {
            out.print("Invalid room number. Enter another room number (row and column separated by a space) ");
            r=kb.nextInt();
            c=kb.nextInt();
            kb.nextLine();
        }
        room[r][c] = "open";

    }
    printMatrix(room);
}

【问题讨论】：

标签： java arrays loops multidimensional-array infinite-loop

【解决方案1】：

去掉else if (a.equalsIgnoreCase("Q"));上的分号

; 结束语句，这意味着break 总是完成，而不仅仅是在满足条件时。

【讨论】：

非常感谢。那些分号总是出来找我哈哈哈。

【解决方案2】：

而不是使用

for(;;)
{
    out.print("Would you like to reserve or release a room? Type Q to exit ");
    a = kb.nextLine();

    if (a.equalsIgnoreCase("reserve"))
    {
        out.print("How many rooms would you like to reserve? ");
        int num = kb.nextInt();
        reserveRooms(rooms, num);
    }
    else if (a.equalsIgnoreCase("release"))
    {
        out.print("How many rooms would you like to release? ");
        int x = kb.nextInt();
        releaseRooms(rooms, x);
    }
    else if (a.equalsIgnoreCase("Q"));
        break;
}

为什么不使用

while (!a.equalsIgnoreCase("Q"))
{
    out.print("Would you like to reserve or release a room? Type Q to exit ");
    a = kb.nextLine();

    if (a.equalsIgnoreCase("reserve"))
    {
        out.print("How many rooms would you like to reserve? ");
        int num = kb.nextInt();
        reserveRooms(rooms, num);
    }
    else if (a.equalsIgnoreCase("release"))
    {
        out.print("How many rooms would you like to release? ");
        int x = kb.nextInt();
        releaseRooms(rooms, x);
    }
    else 
    {
        //do nothing
    }
}

【讨论】：

【解决方案3】：

去掉分号;:

改变

else if (a.equalsIgnoreCase("Q"));

到

else if (a.equalsIgnoreCase("Q"))

【讨论】：