Question

在我的情况1中，当用户决定停止存储任何项目时，我试图读取输入。用户按回车键，我希望程序返回菜单部分。此外，我想在案件结束后每次都返回菜单。我该怎么办？

 import java.text.*;
 import java.util.*;


 public class MonthlyExpenditure { 
    static Scanner input= new Scanner(System.in).useDelimiter("\r\n");
    static DecimalFormat fmt=new DecimalFormat("0.00");

    public static void main(String[] args ) 
    {
        int choice, month=0,i=0,j=month ;

        String b; 




        double[] totalAmount= new double[12];
        String[][] item= new String [12][11]; //12= column(month), 11=row(item)
        double[][] amount= new double[12][11]; //12=column(month), 11=row(amount)






        System.out.println("************* Expenditure ***************");
        System.out.println("1> Enter monthly expenses");
        System.out.println("2> Display detailed expenditure by month");
        System.out.println("3> Quick glance at monthly expenses");
        System.out.println("4> Exit");
        System.out.print("Please select your choice <1-4>");
        choice=input.nextInt();
        System.out.println("*****************************************");
        switch(choice)
        {
        case 1 : 



            System.out.print("Enter month <1 for Jan - 12 for Dec>: ");
            month=input.nextInt();
            b=getMonth(month);
            System.out.println(b+" expenditure <max 10 items>"); 

            while(i<10){                //repeat asking user to enter up to 10 item

            j=month;
            System.out.print("Enter item "+(i+1)+" <Press ENTER to exit> : "); //"while" to only prompt enter item and amount
            item[j][i]=input.next();
            if(item[j][i]==" ")
                System.out.println("meunu");


            System.out.print("Enter amount : ");
            amount[j][i]=input.nextDouble();  
            i++;
            }

            break;


        case 2 : 
            System.out.print("Enter month <1 for Jan - 12 for Dec>: ");

            month=input.nextInt();
            b=getMonth(month);
            j=month;
            System.out.println("Expenditure for "+b);

            i=0;

            while(item[j][i]!=null) 
            {   System.out.println(item[j][i]+"\t\t\t"+amount[j][i]);
            i++;

        }

            break;


        case 3 : 
            System.out.println("Monthly expenditure :");
            System.out.println(" ");
            {
            b=getMonth(month);
            j=month;


            totalAmount[j]=amount[j][0]+amount[j][1]+amount[j][2]+amount[j][3]+amount[j][4]+amount[j][5]+amount[j][6]+amount[j][7]+amount[j][8]+amount[j][9];
            System.out.print(b+"\t\t$"+totalAmount[j]);
            if(totalAmount[j]>2500)
                System.out.println("\t\t\t over spent!!");
            else
                System.out.println(" ");
            }
            break;


        case 4 : 
            System.out.println("Thank you for using this System");
            System.exit(0);
            break;

        default : 
            System.out.println("Error. Enter only 1-4");

            break;






        }while(choice<1||choice>4);

            }

    public static String getMonth(int b)

    {

    String month=" ";

    switch (b) {

    case 1:month="Jan";

    break;

    case 2:month="Feb";

    break;

    case 3:month="Mar";
    break;

    case 4:month="Apr";

    break;

    case 5:month="May";

    break;

    case 6:month="Jun";

    break;

    case 7:month="Jul";

    break;

    case 8:month="Aug";

    break;

    case 9:month="Sep";

    break;

    case 10:month="Oct";

    break;

    case 11:month="Nov";

    break;

    case 12:month="Dec";
    break;

    default: System.out.println("Invalid number. Only 1-12 is recognisable.");



    }//end switch
    return month;}

Answer 1

在这种情况下不要使用nextInt，而是nextLine()，然后使用Integer.parseInt()进行解析。

Answer 2

如果您想允许用户在switch语句中的操作内的任何位置取消，您需要首先使用Scanner#nextLine()读取他们的输入，然后测试该行是否等于空 - 串。如果是的话，就爆发了。

String line = input.nextLine();
if (line.equals(""))
{
    break; // Go to next-line after inner-most loop/switch structure
}
// Code for basic course of events

要再次将用户返回到菜单，您可以将代码的相关部分（即：从打印菜单的位置到switch语句的末尾）包装在某种类似的循环中。

do {
    // Your code to print out the menu and perform operations here
} while (choice != 4); // Replace 4 with whatever value associated with an exit command

Answer 3

一个简单的解决方案就是将所有内容包装在while（true）循环中。您可以将菜单创建字符串移动到静态方法，只需在需要再次显示菜单时调用该方法。

这样的事情应该对createMenu方法有用，你可能想要处理用户不输入整数的情况。

private static int createMenu() {
    System.out.println("************* Expenditure ***************");
    System.out.println("1> Enter monthly expenses");
    System.out.println("2> Display detailed expenditure by month");
    System.out.println("3> Quick glance at monthly expenses");
    System.out.println("4> Exit");
    System.out.print("Please select your choice <1-4>: ");
    int choice = Integer.parseInt(input.nextLine());
    System.out.println("*****************************************");
    return choice;
}

你的主要方法可以这样开始：

    public static void main(String[] args) {
        int choice, month = 0, i = 0, j = month;
        String b;
        double[] totalAmount = new double[12];
        String[][] item = new String[12][11]; //12= column(month), 11=row(item)
        double[][] amount = new double[12][11]; //12=column(month), 11=row(amount)
        while (true) {
            choice = createMenu();
            switch (choice) {
                 // etc

当用户点击返回键时，您可以突破内部while循环：

if (item[j][i].isEmpty()) {
    break;
}

Java问题（需要帮助）

3 个答案: