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How do I convert this if-else statement into a switch statement in java?

The prompt is:
Convert the following if-else-if statement into a switch statement. Don’t rewrite the constants or variable definitions, just the if statement.
final char BLT = 'b';
final char VEGAN = 'v';
final char TUNA = 't';
final char ROAST_BEEF = 'r';
double price;
int sandwichType;
System.out.println("Enter sandwich type: ");
sandwichType = keyboard.nextLine().charAt(0);
if (sandwichType == VEGAN || sandwichType == TUNA) {
price = 3.99;
} else if (sandwichType == BLT) {
price = 4.19;
} else if (sandwichType == ROAST_BEEF) {
price = 4.99;
} else {
System.out.println("That's not a valid sandwich type.");
System.exit(0); // This ends the program
}
System.out.println("Your total is is $" + (price*1.0825));
My current code is this:
switch (sandwichType) {
case 1:System.out.println("The price is $" + (3.99*1.0825));
case 2: System.out.println("The price is $" + (4.19*1.0825));
case 3: System.out.println("The price is $" + (4.99*1.0825));
break;

You are forgetting breaks in between the switch cases. You also will want to use the char names of the different sandwiches instead of numbers. Finally, if none of the cases match the given sandwhichType, you'll want to have a default case, this would be essentially be your else statement from the previous code. The one tricky piece is the first case which accepts two different types which can be done by having a case followed by another case.
switch (sandwhichType)
{
case VEGAN:
case TUNA:
price = 3.99;
break;
case BLT:
price = 4.19;
break;
case ROAST_BEEF:
price = 4.99;
break;
default:
System.out.println("That's not a valid sandwich type.");
System.exit(0);
break;
}
System.out.println("Your total is is $" + (price*1.0825));

The cases should be options
case BLT:
You also need a default case
default:
break;
And break; after every case.

Java switch statement not working properly

I have two classes for calculating the cost of an ISP plan and gathering input/displaying the cost. ISPMain.java and ISP.java ISPMain is supposed to display service plans and ask the user to select their plan by the letter of the package, like package a, package b, or package c. I have it set up so the user inputs the character to choose the plan. If the plan is the not package c (unlimited plan) the user is prompted to enter the hours they used.
Once the hours are entered and stored in hoursUsed, ISP.java calculates the cost and then ISPMain.java displays it. My problem is that my switch statement in ISP only is displaying the default value and I am not sure why. Can anyone explain?
public class ISPMain
{
public static void main(String[] args)
{
char pkg;
double hoursUsed;
Scanner kb = new Scanner(System.in);
System.out.println("The three packages offered are: ");
System.out.println("Package A: For $9.95 per month, 10 hours of access are provided. \nAdditional hours are $2.00 per hour.");
System.out.println("Package B: For $14.95 per month, 20 hours of access are provided. \nAdditional hours are $1.00 per hour.");
System.out.println("Package C: For $19.95 per month, unlimited access is provided.");
System.out.println("Please type the letter of the package you have: ");
pkg = kb.nextLine().toUpperCase().charAt(0);
if(pkg == 'A')
{
System.out.print("Enter number of hours: ");
hoursUsed = kb.nextDouble();
}
else if(pkg == 'B')
{
System.out.print("Enter number of hours: ");
hoursUsed = kb.nextDouble();
}
else if(pkg == 'C')
{
System.out.print("You have unlimited access! No need to enter hours used. \n");
}
ISP user = new ISP();
System.out.print("Total charges: " + user.calculateCharges());
}
}
switch statement from ISP.java:
public double calculateCharges()
{
switch (pkg)
{
case 'A':
if (hoursUsed < 10)
{
return 9.95;
}
else
{
return (hoursUsed - 10)*2 + 9.95;
}
case 'B':
if (hoursUsed < 20)
{
return 14.95;
}
else
{
return (hoursUsed - 20) + 14.95;
}
case 'C':
return 19.95;
default:
System.out.println("Invalid input!");
return 0;
}
}
to conclude, my if else works fine, but the switch only displays "Invalid input"

As others have said, you need to get the pkg variable into the scope of your switch statement. Try this:
public double calculateCharges(char pkg){
switch(pkg){
case('A'):{
//insert code here
break;
}
case('B'):{
//insert code here
break;
}
case('C'):{
//insert more code here
break;
}
default:{
//code here
break;
}
}
}
Then call your method like:
System.out.print("Total charges: " + user.calculateCharges(pkg));

The default: case statement will always run in your code because char pkg isn't defined as a parameter for your method.
The user may enter A, B, or C, but since it does not get passed the end result will always be default, therefore causing your Invalid input.
Try :
public double calculateCharges(char pkg){
switch (pkg)
{
case 'A':
if (hoursUsed < 10){
return 9.95;
}else{
return (hoursUsed - 10)*2 + 9.95;
}
case 'B':
if (hoursUsed < 20){
return 14.95;
}else{
return (hoursUsed - 20) + 14.95;
}
case 'C':
return 19.95;
default:
System.out.println("Invalid input!");
return 0;
}

Initializing a non-numeric variable in Java [duplicate]

This question already has answers here:
Variable might not have been initialized error
(12 answers)
Closed 7 years ago.
To practice using if else, do while, and switch statements, I was making a small text adventure game where a user would be able to input their name, gain a randomly generated profession, and be assigned a randomly generated quest. however, halfway though the second goal, the java development program I was using continually said that one of my variables "might not have been initialized".
This is what i have for the code so far:
============
import java.util.*;
public class Adventure1
{
public static void main(String[] args)
{
//initialize variables
Scanner keyboard = new Scanner(System.in);
Scanner keyboardYN = new Scanner(System.in);
Scanner keyboard2YN = new Scanner(System.in);
String name = "";
char userInput;
char userYN;
char user2YN;
int dieRoll = (int) (Math.random() * 9);
char outputType;
char Mage;
char Soldier;
char Explorer;
char howTo;
//exeternal documation
System.out.println("The First Adventure by K. Konieczny ");
System.out.println();
//player name
do
{
System.out.println();
System.out.print("What is your name: ");
name = keyboard.nextLine();
//prompt
System.out.print("So your name is " + name + "? Are you sure y/n : ");
userYN = keyboardYN.nextLine().charAt(0);
System.out.println();
if(userYN == 'y')
{
System.out.println();
}
else
{
System.out.println("Type in your real name.");
}
}//end do
while(userYN == 'n');
//narration pt. 1
System.out.println("You, " + name +
" have just been named the greatest, uh, what was it again?");
System.out.println();
//specialization
System.out.print("Roll the dice to decide what your profession is? y/n : ");
user2YN = keyboard2YN.nextLine().charAt(0);
if(user2YN == 'y')
{
switch (dieRoll)
{
case '0':
case '1':
case '2': outputType = Mage;
case '3':
case '4':
case '5': outputType = Soldier;
case '6':
case '7':
case '8': outputType = Explorer;
default : outputType = howTo;
}//end switch
System.out.println("Oh right, you are the greatest " + outputType + " in the town.");
}
else
{
System.out.println("I must be thinking of someone else then.");
}
//get quest
System.out.println();
System.out.println("End of program");
}//end main
}//end class
============
The error message i get reads "variable Mage might not have been initialized."
I don't have much coding experience, and was wondering what I did wrong and how I could fix it in future programs.

You have:
char Mage;
// ...
case '2': outputType = Mage;
What is the value of Mage at that point? The compiler is warning you that the variable has not been initialized.
You might want to initialize Mage to some value such as:
char Mage = '0';
Or most likely you want a String representation of Mage:
String outputType;
String mage = "Mage";
String soldier = "Soldier";
String explorer = "Explorer";
// ...
switch (dieRoll) {
case '0':
case '1':
case '2': outputType = mage;
break;
case '3':
case '4':
case '5': outputType = soldier;
break;
case '6':
case '7':
case '8': outputType = explorer;
break;
default : outputType = "Oops";
}

When I run my program i get the error java.lang.StringIndexOutOfBoundsException: String index out of range: 0

here is my code
import java.io.*;
import java.util.*;
public class weightOnOtherPlanets {
public static void main(String[] args) {
Scanner kbReader = new Scanner(System.in);
System.out.println("Enter your weight");
double weight = kbReader.nextDouble();
System.out.println("choose a planet by entering the corresponging letter\n");
System.out.println("A. Voltar");
System.out.println("B. Krypton");
System.out.println("C. Fertos");
System.out.println("D Servantos");
String choice = kbReader.nextLine( );
char p = choice.charAt(0);
String answerPhrase = "Your weight is " + " " ;
switch(p){
case 'A':
case 'a':
System.out.println(answerPhrase +(.091*weight));
break;
case 'B':
case 'b':
System.out.println(answerPhrase + (.720*weight));
break;
case 'C':
case 'c':
System.out.println(answerPhrase + (.865*weight));
break;
case 'D':
case 'd':
System.out.println(answerPhrase + (4.612*weight));
break;
default:
System.out.println("Please enter either A,B,C,or D");
break;
}
}
}
I have used almost the exact same code for another similar practice project and it worked just fine. When i run the program it goes to the point where it asks for a weight input, then it displays the choice list, but with the error message exception in "main":
java.lang.StringIndexOutOfBoundsException: String index out of range: 0
at java.lang.String.charAt(String.java:686)
at weightOnOtherPlanets.main(weightOnOtherPlanets.java:14)
I don't know why it gives this error before allowing keyboard input for String choice.

This is because of the way Scanner scans lines.
After you enter a double (the weight), you press Return. This tells System.in to take all the characters you entered and pass them to the scanner. The scanner then reads the part that interests it - the double number - but leaves everything else waiting for the next operation.
This means the Return you pressed - the end-of-line - is still there. Now, the next thing is nextLine(). The scanner sees it, and it reads all the characters it has until it finds an end-of-line. But as we said, the end-of-line is right there. So it reads that, and gives you all the characters it found before it. Which is none at all, because there were no other characters between the double number and the end-of-line.
This means you get an empty string. And an empty string doesn't have a character at position 0, because that would mean it was not empty.
So what you should do is, after receiving the double, you should add a kbReader.nextLine(); - just like that, without putting the value anywhere. This will skip the end-of-line you entered for the double, and then you'll get the next line properly.
When you do your menu reading, though, you should be checking that the string is not empty before you call charAt(0). After all, the user can decide to press Return rather than make a valid choice. So your system should either ignore that or tell him that it's not a legal input, rather than fail with an exception.

You call nextDouble(); and after that you call nextLine() to get your answer phrase. But that call to nextLine(); will only consume the rest of the line on which you entered your double and it will be empty, therefore choice.charAt(0); will throw an exception.
Try doing something like this to consume the rest of the line and then call the nextLine() to get the answer phrase.
System.out.println("Enter your weight");
double weight = kbReader.nextDouble();
kbReader.nextLine(); // Consume the rest of the line
// ...
String choice = kbReader.nextLine(); // Get the actual input
char p = choice.charAt(0);

try this:
public static void main(String[] args) {
Scanner kbReader = new Scanner(System.in);
System.out.println("Enter your weight");
double weight = kbReader.nextDouble();
System.out.println("choose a planet by entering the corresponging letter\n");
System.out.println("A. Voltar");
System.out.println("B. Krypton");
System.out.println("C. Fertos");
System.out.println("D Servantos");
String choice = kbReader.nextLine();
if (choice.isEmpty()) {
choice = kbReader.nextLine();
}
char p = choice.charAt(0);
String answerPhrase = "Your weight is " + " ";
switch (p) {
case 'A':
case 'a':
System.out.println(answerPhrase + (.091 * weight));
break;
case 'B':
case 'b':
System.out.println(answerPhrase + (.720 * weight));
break;
case 'C':
case 'c':
System.out.println(answerPhrase + (.865 * weight));
break;
case 'D':
case 'd':
System.out.println(answerPhrase + (4.612 * weight));
break;
default:
System.out.println("Please enter either A,B,C,or D");
break;
}
}

You need to read for input differently. That's why you are throwing an exception.
char p = choice.charAt(0); // why not just do a string comparison instead?
is where the error comes up. This is because choice is null / has no charAt(0).
Irregardless I would use something like this instead
char p = ''
while(in.hasNext()) {
String input = in.nextLine();
if (p.length()>0){
p = choice.charAt(0);
}
//do whatever you wanted to with p
This should give you the behavior you are looking for.
Don't forget to consider changing the double input to work roughly the same though.

GPA calculator using while loop with switch statement. Java source code

I need to be able to press 'q' in the while loop to get it to exit the loop. I then need the code to be able to display the credit hours with the grade beside it. Next I have to display their GPA according to the input of their hours and their grades. Everytime I press 'q' to exit, the program stops and doesn't display anything. Please help!
package shippingCalc;
import javax.swing.JOptionPane;
public class Gpa {
public static void main(String[] args) {
String input = "";
String let_grade;
int credits = 0;
double letterGrade = 0;
int course = 1;
String greeting = "This program will calculate your GPA.";
JOptionPane.showMessageDialog(null, greeting,"GPA Calculator",1);
while(!input.toUpperCase().equals("Q"))
{
input = JOptionPane.showInputDialog(null, "Please enter the credits for class " + course );
credits = Integer.parseInt(input);
course ++;
input = JOptionPane.showInputDialog(null,"Please enter your grade for your " +credits + " credit hour class");
let_grade = input.toUpperCase();
char grade = let_grade.charAt(0);
letterGrade = 0;
switch (grade){
case 'A': letterGrade = 4.00;
break;
case 'B': letterGrade = 3.00;
break;
case 'C': letterGrade = 2.00;
break;
case 'D': letterGrade = 1.00;
break;
case 'F': letterGrade = 0.00;
break;
}
}
JOptionPane.showMessageDialog(null, course++ + "\n\n It Works" + letterGrade);
}
}

The issue I think is that credits is an int and right after the second popup
input = JOptionPane.showInputDialog(null,
"Please enter the credits for class " + course);
You assign whatever the user types to the int credits, so if you input a String q or Q its gonna break. Also, keep in mind that the while loop condition is only checked once per iteration, at the start of the iteration, so it won't know about the value of input until that time
There are a couple ways you could fix this. A quick and easy way would be to insert this line of code before assigning the user input to credit
if(input.equalsIgnoreCase("q")){
continue;//will allow input to be checked immediately before assigning to credits
}