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Java, How to close do-while loop using multiple character boolean expressions?

This is quite a beginner question but I'm wondering why my do...while loop is not closing.
The program is supposed to loop while the user input is not 'C', 'c', 'F', or 'f'.
It seems to close when just one boolean expression in the while section is valid but not if multiple are valid.
public class CelsToFaren
{
public static void main(String[] args)
{
// scanner setup
Scanner sc = new Scanner(System.in);
// Variable declarations
int celsius;
int answerC;
int farenheit;
int answerF;
char userLetter;
do
{
// initial menu options
System.out.println("Which temperature would you like to convert from? ");
System.out.println(" >(C)elsius ");
System.out.println(" >(F)arenheit ");
// user input of C, c, F, or f to select option
userLetter = sc.next().charAt(0);
// if user input C or c
if ((userLetter == 'C' || userLetter == 'c'))
{
System.out.print("Please enter the temperature: ");
celsius = sc.nextInt();
answerC = ((celsius*9/5)+32);
System.out.println("The answer is: " + answerC + " Farenheit ");
}
else
{
// if user input F or f
if ((userLetter == 'F' || userLetter == 'f'))
{
System.out.print("Please enter the temperature: ");
farenheit = sc.nextInt();
answerF = ((farenheit-32)*5/9);
System.out.println("The answer is: " + answerF + " Celsius ");
}
else
{
// if user input not F, f, C, or c
if ((userLetter != 'F' || userLetter != 'f' || userLetter != 'C' || userLetter != 'c'));
{
System.out.println("Please enter a valid option");
}
}
}
} while ((userLetter != 'c') || (userLetter != 'C') || (userLetter != 'f') || (userLetter != 'F'));
}
}

You need to change the exit logic.
In your case 1 | 0 | 0 = true so the loop continues.
You need to change it to:
while ((userLetter != 'c') && (userLetter != 'C') && (userLetter != 'f') && (userLetter != 'F'));

Your condition is wrong. Lets assume you want to break loop in if statement. It would look like
if(userLetter == 'c' || userLetter == 'C' || userLetter == 'f' || userLetter == 'F')
Now let's apply negation to get a condition under which you do not need to exit the loop
if(!(userLetter == 'c' || userLetter == 'C' || userLetter == 'f' || userLetter == 'F'))
this condition is simillar to
if(userLetter != 'c' && userLetter != 'C' && userLetter != 'f' && userLetter != 'F')

Java - Get user input and transferring to main function with Switch case

I have a static function which gets and returns a char input.
It will then check the input using a while loop.
After my main method gets the input, the result will display accordingly to the user input.
Below is my method:
public class test
{
public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
char choice = getInput(sc);
String result;
switch (choice)
{
case ('a'): result = "u choose A";
break;
}
}
private static char getInput(Scanner keyboard)
{
Scanner sc = new Scanner(System.in);
System.out.println("a, b, c, d, e, q: ");
char choice = sc.nextLine().trim().toLowerCase().charAt(0);
while (choice != 'a' || choice != 'b' || choice != 'c' || choice != 'd' || choice != 'e' || choice != 'q')
{
System.out.println("You have entered an invalid entry.");
System.out.println("a, b, c, d, e, q: ");
choice = sc.nextLine().trim().toLowerCase().charAt(0);
}
return choice;
}
}
However, I am getting the result of invalid input even though I entered the character 'a'.
May I know which part have I gone wrong?

This condition:
while (choice != 'a' || choice != 'b' || choice != 'c' || choice != 'd' || choice != 'e' || choice != 'q')
will always return true if your choice is not a or is not b or is not c, etc. Change those || operators to && operators and you should be good to go.

Convert Uppercase Letter Input to a specific Number

I'm super new to programming so I would love to keep this simple. The compiler accepts my code, but when I run the program and type in for example the letter A I just get a ton of errors. I tried earlier using String letter instead of int letter, but I just got compiler errors stating I couldn't convert Strings to characters or something. I'm really confused and could use a quick explanation and fix so I can get a number back. Here's my code:
import java.util.Scanner;
import java.lang.String;
public class PhoneAlgorithm {
public static void main(String[] args){
int digit = -1;
Scanner in;
in = new Scanner(System.in);
System.out.print("Enter an uppercase letter to find out the corresponding digit on a telephone: ");
int letter;
letter = Integer.parseInt(in.next());
if (letter == 'A' || letter == 'B' || letter == 'C') {
digit = 2; }
else if (letter == 'D' || letter == 'E' || letter == 'F') {
digit = 3; }
else if (letter == 'G' || letter == 'H' || letter == 'I') {
digit = 4; }
else if (letter == 'J' || letter == 'K' || letter == 'L') {
digit = 5; }
else if (letter == 'M' || letter == 'N' || letter == 'O') {
digit = 6; }
else if (letter == 'P' || letter == 'Q' || letter == 'R' || letter == 'S') {
digit = 7; }
else if (letter == 'T' || letter == 'U' || letter == 'V') {
digit = 8; }
else if (letter == 'W' || letter == 'X' || letter == 'Y' || letter == 'Z') {
digit = 9; }
else if (letter >= 'a' && letter >= '3') {
System.out.print("You did not enter a valid uppercase letter. Try again!");
}
if (digit != -1) {
System.out.println("The corresponding digit on your telephone is: " + digit);
}
}
}

When you use parseInt(str), you will get an Exception if the parameter str cannot be converted to an integer.
You must use char, since you are comparing the input with single characters:
char letter;
letter = in.nextLine().charAt(0);
str.charAt(index) Returns the char value at the specified index.

I have modified your code, I guess this is what you are looking for..
import java.util.Scanner;
public class Try {
public static void main(String[] args) {
//declarations
char letter;
int digit=0;
// Asking the user to enterstring
System.out.println("Enter the string");
String enterString;
//creating a scanner object and reading the string
Scanner input = new Scanner(System.in);
enterString= input.next();
System.out.println("Entered string is "+enterString);
int temp=0;
for(int i=0;i<enterString.length();i++){
letter=(char)enterString.codePointAt(i);
if (letter == 'A' || letter == 'B' || letter == 'C') {
digit = digit*10+2; }
else if (letter == 'D' || letter == 'E' || letter == 'F') {
digit = digit*10+3; }
else if (letter == 'G' || letter == 'H' || letter == 'I') {
digit = digit*10+4; }
else if (letter == 'J' || letter == 'K' || letter == 'L') {
digit = digit*10+5; }
else if (letter == 'M' || letter == 'N' || letter == 'O') {
digit = digit*10+6; }
else if (letter == 'P' || letter == 'Q' || letter == 'R' || letter == 'S') {
digit = digit*10+7; }
else if (letter == 'T' || letter == 'U' || letter == 'V') {
digit = digit*10+8; }
else if (letter == 'W' || letter == 'X' || letter == 'Y' || letter == 'Z') {
digit = digit*10+9; }
else if (letter >= 'a' && letter >= '3') {
System.out.print("You did not enter a valid uppercase letter. Try again!");
}
/*if (digit != 0) {
System.out.println("The corresponding digit on your telephone is: " + digit);
}*/
}
if (digit != 0) {
System.out.println("The corresponding digit on your telephone is: " + digit);
}
}
}

Key input restrictions

How do you restrict the letter being inputted;
for example I have the code
System.out.println("Enter a letter(A,B,C or D):");
letter = input.next().charAt(0);
How would I set up an if statement to say if letter does not equal "A" "B" "C" or "D", it will say please input correct letter?
thanks

I would recommend you to use a while loop, so it loops until you get a valid input:
Scanner input = new Scanner(System.in);
System.out.println("Enter a letter(A,B,C or D):");
char letter = input.next().charAt(0);
while (letter != 'A' && letter != 'B' && letter != 'C' && letter != 'D') {
System.out.println("Enter a valid letter(A,B,C or D):");
letter = input.next().charAt(0);
}
System.out.println(letter);
Output:
Enter a letter(A,B,C or D):
E
Enter a valid letter(A,B,C or D):
A
Valid: A
But if you just want an if conditional, use the same condition of the while above:
if (letter != 'A' && letter != 'B' && letter != 'C' && letter != 'D') {
...
}

Java scanner not storing string properly

I am trying to create a menu in the console and have the user select an option, for some reason when I run the application it goes straight to the else, bypassing options a-d.
import java.util.Scanner;
public class UserChoice {
public static void main(String[] args)
{
boolean status = true;
while (status == true)
{
System.out.println("");
System.out.println("MENU");
System.out.println("");
System.out.println("A : String Functions");
System.out.println("B : Simple Arithmetic Functions");
System.out.println("C : Temperature Conversion");
System.out.println("D : Sequences");
System.out.println("E : Exit Application");
System.out.println("");
System.out.println("Please make a selection.");
Scanner keyboard = new Scanner(System.in);
String choice =null;
choice = keyboard.nextLine();
if (choice == "a" || choice == "A")
{
StringFunctions();
}
else if (choice == "b" || choice == "B")
{
ArithmeticFunctions();
}
else if (choice == "c" || choice == "C")
{
TemperatureConversion();
}
else if (choice == "d" || choice == "D")
{
Sequences();
}
else if (choice == "e" || choice == "E")
{
System.exit(0);
}
else
{
System.out.println("You have entered an invalid selection, please choose again.");
}
}
}

All String/Object comparisons should use equals() method instead of == (except String literals)
if (choice.equals("a") || choice .equals( "A")){....}
Apply same change to other else/if blocks also.
== compares reference equality. equals() method checks for content equality.

You may want to make sure that at least one character is entered:
String choiceString ="";
while(choiceString.length() <1){
choiceString = keyboard.nextLine();
}
Once done, you may want to get the first character from the string as:
char choice = choiceString.charAt(0);
now since your choice is char, you may write your conditions using single quote as below:
if (choice == 'a' || choice == 'A'){
.......
......
Also if you want, you want to change the case of String entered to upper or lower case, get the char and then use simpler conditions as below:
char choice = choiceString.toUpperCase().charAt(0);
if (choice == 'A'){
.....
}else if(...