使用案例后如何制作 Java 主菜单循环

Question

我对 Java 还是个新手，但由于熟悉其他一些编程语言，我知道其中很多的基本布局。我苦苦挣扎的一件事是循环菜单，特别是主菜单。

我不知疲倦地研究了它的方法，但 none 似乎适用于我的程序。我假设它是我在更基本的程序中遗漏的一些愚蠢和小的东西。

在下方查看，感谢任何提示。

    import java.util.Scanner;
public class basicCalc {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Scanner input = new Scanner(System.in);
        boolean mainLoop = true;

        int choice;
        do{
            System.out.println("Calculator Main Menu\n");
            System.out.print("1.) Addition \n");
            System.out.print("2.) Subtraction.\n");
            System.out.print("3.) Multiplication.\n");
            System.out.print("4.) Division.\n");
            System.out.print("5.) Generate Random Number.\n");
            System.out.print("6.) Exit\n");
            System.out.print("\nEnter Your Menu Choice: ");

            choice = input.nextInt();


        }

        while(choice >7);

        switch(choice){

        case 1:
            //Definitions
            int adNumf, adNuml, sum;
            System.out.print("Please Enter The First Number: ");
            adNumf = input.nextInt();
            System.out.print("\nPlease Enter The Second Number: ");
            adNuml = input.nextInt();
            sum = adNumf + adNuml;
            System.out.print("The Sum Of Those Numbers is: " +sum);
            break;

        case 2: 
            int subNum1, subNum2, sum2;
            System.out.println("\nPlease Enter The First Number: ");
            subNum1 = input.nextInt();
            System.out.println("Please Enter The Second Number: ");
            subNum2 = input.nextInt();
            sum2 = subNum1 - subNum2;
            System.out.println("The Subtraction Leaves The Number: " +sum2);
            break;

        case 3:
            int multNum1, multNum2, multTotal;

            // Gather Input
            System.out.println("Please Enter The First Number To Multiply: ");
            multNum1 = input.nextInt();
            System.out.println("Please Enter The Second Number To Multiply: ");
            multNum2 = input.nextInt();

            // This will Multiply the Numbers
            multTotal = multNum1 * multNum2;

            //Display Final
            System.out.println("The Multiplied Numbers Are: " +multTotal);
            break;

        case 4: 
            //Definitions
            double divNum1, divNum2, divTotal;
            System.out.println("Enter Your Numerator ");
            divNum1 = input.nextInt();
            System.out.println("Enter Your Denominator ");
            divNum2 = input.nextInt();
            if(divNum2 == 0){
                System.out.println("Zero is Not divisable, please select a new denominator: ");
                divNum2 = input.nextInt();
            }
            divTotal = divNum1 / divNum2;
            System.out.println("Your divisor is: " +divTotal);
            break;

        case 5:
            double limL, limH, rand;
            System.out.println("Enter Your Low Limit: ");
            limL = input.nextInt();
            System.out.println("Enter Your High Limit ");
            limH = input.nextInt();

            //Equation to keep numbers within bounds
            rand = limL + (Math.random() * ((limH - limL) + 1));
            System.out.println("Given Your Limits, the Random Number will be: " +rand);
            break;

        case 6: 
            System.out.println("Exiting Program...");
            System.exit(0);
             break;
        }



        // Bad Menu Option Direct
    if (choice > 6 || choice < 1){
        System.out.println("This is not a valid Menu Option! Please Select Another.");
        do{
            choice = input.nextInt();
        }
        while(choice < 7 );
    }
    // End bad menu option  


    }

}

Answer 1

您可以在 while 循环中给出整个代码（从显示菜单开始）并将条件设为 true，这样在使用 case 后它会自动重复（就像您使用 6 退出一样）。如果为 eg:10 提供了任何无效输入，则案例将转到默认部分并执行那里的代码

import java.util.Scanner;
public class basicCalc {

public static void main(String[] args) {
    // TODO Auto-generated method stub

    Scanner input = new Scanner(System.in);
    boolean mainLoop = true;

    int choice;
    while(true){
        System.out.println("Calculator Main Menu\n");
        System.out.print("1.) Addition \n");
        System.out.print("2.) Subtraction.\n");
        System.out.print("3.) Multiplication.\n");
        System.out.print("4.) Division.\n");
        System.out.print("5.) Generate Random Number.\n");
        System.out.print("6.) Exit\n");
        System.out.print("\nEnter Your Menu Choice: ");

        choice = input.nextInt();




    switch(choice){

    case 1:
        //Definitions
        int adNumf, adNuml, sum;
        System.out.print("Please Enter The First Number: ");
        adNumf = input.nextInt();
        System.out.print("\nPlease Enter The Second Number: ");
        adNuml = input.nextInt();
        sum = adNumf + adNuml;
        System.out.print("The Sum Of Those Numbers is: " +sum);
        break;

    case 2: 
        int subNum1, subNum2, sum2;
        System.out.println("\nPlease Enter The First Number: ");
        subNum1 = input.nextInt();
        System.out.println("Please Enter The Second Number: ");
        subNum2 = input.nextInt();
        sum2 = subNum1 - subNum2;
        System.out.println("The Subtraction Leaves The Number: " +sum2);
        break;

    case 3:
        int multNum1, multNum2, multTotal;

        // Gather Input
        System.out.println("Please Enter The First Number To Multiply: ");
        multNum1 = input.nextInt();
        System.out.println("Please Enter The Second Number To Multiply: ");
        multNum2 = input.nextInt();

        // This will Multiply the Numbers
        multTotal = multNum1 * multNum2;

        //Display Final
        System.out.println("The Multiplied Numbers Are: " +multTotal);
        break;

    case 4: 
        //Definitions
        double divNum1, divNum2, divTotal;
        System.out.println("Enter Your Numerator ");
        divNum1 = input.nextInt();
        System.out.println("Enter Your Denominator ");
        divNum2 = input.nextInt();
        if(divNum2 == 0){
            System.out.println("Zero is Not divisable, please select a new denominator: ");
            divNum2 = input.nextInt();
        }
        divTotal = divNum1 / divNum2;
        System.out.println("Your divisor is: " +divTotal);
        break;

    case 5:
        double limL, limH, rand;
        System.out.println("Enter Your Low Limit: ");
        limL = input.nextInt();
        System.out.println("Enter Your High Limit ");
        limH = input.nextInt();

        //Equation to keep numbers within bounds
        rand = limL + (Math.random() * ((limH - limL) + 1));
        System.out.println("Given Your Limits, the Random Number will be: " +rand);
        break;

    case 6: 
        System.out.println("Exiting Program...");
        System.exit(0);
         break;
    default :
             System.out.println("This is not a valid Menu Option! Please Select Another");
             break;

    }


    }




    }

   }

Answer 2

或者试试这个

import java.util.Scanner;
public class basicCalc {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Scanner input = new Scanner(System.in);
        boolean mainLoop = true;

        int choice;
        do{
            System.out.println("Calculator Main Menu\n");
            System.out.print("1.) Addition \n");
            System.out.print("2.) Subtraction.\n");
            System.out.print("3.) Multiplication.\n");
            System.out.print("4.) Division.\n");
            System.out.print("5.) Generate Random Number.\n");
            System.out.print("6.) Exit\n");
            System.out.print("\nEnter Your Menu Choice: ");
            choice = input.nextInt();




        switch(choice){

        case 1:
            //do something
            break;

        case 2: 
            //do something
            break;

        case 3:
            //do something
            break;

        case 4: 
            //do something
            break;

        case 5:
            //do something
            break;

        case 6: 
            System.out.println("Exiting Program...");
            System.exit(0);
             break;
        default:
        System.out.println(choise + " is not a valid Menu Option! Please Select Another.");

    }while(choice != 6 /*Exit loop when choice is 6*/);



    }

}

Answer 3

您对要做什么有一个大致的想法，但是您使循环结束条件变得比需要的更复杂。尝试使用 "default" 选项来捕获超出范围的任何输入。这样您就可以将结束条件简化为“6”（退出情况）。简单展示：

do{
  //Menu options
  System.out.print("6.) Exit\n");
  System.out.print("\nEnter Your Menu Choice: ");

  choice = input.nextInt();

  switch(choice){
        //Your cases from 1 to 6.
        default:
            System.out.println("Invalid menu choice; try again.");
            break;
   }
}while(choice != 6);

如果选择选项不适用于您代码中创建的任何案例，则将调用默认值之后的任何内容。

Answer 4

你的整个执行流程是错误的。您应该将错误的菜单选择检查（在您的情况下为 if）放在 case 之前。要有无限菜单循环，只需添加另一个 if 来打破无限 while-loop。

伪代码：

while(true){
//enter your choice, 8 to exit
  if(choice != valid_range){
//error message
  }
switch(choice){
  case 1: //code
  case 2: //code
  .
  .
  .
  case 7: //code
   if (choice == 8) {
break; //will give flow control to next element after the while statement
   }    
 }
}

使用案例后如何制作 Java 主菜单循环

How to make a Java Main Menu Loop after using a case

java

loops

menu

switch-statement