How to create Menu to Select using Characters A B C or a b c in Java

Question

We need to create a menu that can be selected using Characters such as A. B. C. also a. b. c. and use Q. to quit.

package mainmenu;
import java.util.Scanner;

public class  MainMenu{
public static void main(String[] args){
  System.out.println("       Welcome to our project");
  System.out.println("Please Choose an option from the menu");
  System.out.println("Type the letter to select the option");
  System.out.println();


 // We need to create a menu that can be selected using Characters 
 //such as A. B. C. also a. b. c. and use Q. to quit.

Here we will set a menu with 7 options:

Was looking for a way to create a menu using letters and a way to convert them to a upper case.

/*   A. The Radius of a circle.
  B. The Cost of gym membership over a year.
  C. Compound Interest of CD over 6 years.
  D. The Square Root of a 5 digit number.
  E. Guess the number Game.
  F. Day of your birth day.
  G. Little Shop of Horrors.
  Q. Quit / Exit.
  */

// A. Radius of a Circle
// Scan for the Diameter then display the Results


// B. Cost of a Gym Membership
//   Scan for the Gym info, Name, joining fee, monthly cost, yearly dues,        cancellation fee.
//       double joinFee, monthCost, yearDues, cancelFee.
//       double initialCost = joinFee + monthCost;
//       double yearlyCost = initialCost + (monthCost * 11) + yearDues;
//       double earlycancel = (monthCost * 2 ) + cancelFee;
//       Display the options

// C. Compound Interest of CD over 6 year period
/*
 A=P(1+R)^N     
double amount;      
double principal = 10000 ;      
double rate = .01;                      
for(double months=1; months<=60; months++){         
amount=principal * Math.pow(1 + rate, months);          
System.out.println (months + "  " + amount);        }
*/


// D. Calculate the Square Root of a 5 digit number


// E. Guess the Number Game
//     Too low
//     Too high


// F. Day of the week of your Birthday.
//      Calculate the Day and display


// G. When should Seymour feed the plant
//     Feed me Seymour!!
//     Feed him in the morning, in the afternoon, in the evening and at   midnight.

// Q. Quit / Exit

Answer 1

This code should help:

    Scanner sc = new Scanner(System.in);

    String options = "A. The Radius of a circle.\n" +
    "B. The Cost of gym membership over a year.\n"
    +"C. Compound Interest of CD over 6 years.\n"
    +"D. The Square Root of a 5 digit number.\n" 
    +"E. Guess the number Game.\n"
    +"F. Day of your birth day.\n" 
    +"G. Little Shop of Horrors.\n" 
    +"Q. Quit / Exit.\n";

    String input = null;
    System.out.println("Enter the option you would like to select. Your choices are: ");
    System.out.println(options);
    boolean validInput = false;

    while (!validInput) {
         input = sc.next(); //asks for the user input
         input = input.toUpperCase(); // makes the entire String uppercase
         if (!input.equals("A") || !input.equals("B") || !input.equals("C") || !input.equals("D") || !input.equals("E") || !input.equals("F") || !input.equals("G") || !input.equals("Q")) {
             System.out.println(input+" is not an option");
             System.out.println("Your choices are: ");
             System.out.println(options);
         } else
             validInput = true; //exits the loop when they give something useful.
     }

     if (input.equals("A")) {
         //do A stuff
     } else if (input.equals("B")) {
         //do B stuff
     } else if (input.equals("C")) {
         //do C stuff
     } else if (input.equals("D")) {
         //do D stuff
     } else if (input.equals("E")) {
         //do E stuff
     } else if (input.equals("F")) {
         //do F stuff
     } else if (input.equals("G")) {
         //do G stuff
     } else if (input.equals("Q")) {
         //do Q stuff
     }
     sc.close(); //do this when you are done with the scanner

What it does is it asks for the user's input, then it checks to see if it equals one of the choices. I use

input = input.toUpperCase();

to make the input upper case so that "a" and "A" are recognized as the same thing. Make sure you don't try just

input.toUpperCase();

because that won't do anything. Strings are immutable. Here is more information about that: String is immutable. What exactly is the meaning?

Also, make sure that you use

input.equals("whatever")

Instead of

input == "whatever"

Because the second example is unreliable. More info on this here:How do I compare strings in Java?