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How to use System.out.printf() to display output of number to only two decimal places?

I am creating my first java program for the class. The purpose of the program is to calculate interest for deposit for year one and year two. My issue comes when the code outputs the final totals. The last two lines are supposed to use System.out.printf(). I keep getting the error Exception in thread "main" java.util.UnknownFormatConversionException: Conversion = 'i'. How do I correct this?
public static void main(String... args) {
Scanner keyboard = new Scanner(System.in);
System.out.println("Hello World!");
//declares variables
double interest = 0;
double balance = 0;
double deposit = 0;
double secondYearBalance = 0;
double secondYearInterest = 0;
//displays welcome message
System.out.println("Welcome to George's Interest Calculator");
//prompts user for input
System.out.println("Please enter your initial deposit:");
deposit = keyboard.nextInt();
//Finds outs interest interest earned on deposit
interest = deposit * TAXRATE;
//Finds out the amount of the balance
balance = deposit + interest;
//finds out second year balance
secondYearInterest = balance * TAXRATE;
secondYearBalance = secondYearInterest + balance;
//Outputs totals
System.out.printf("Your balance after one year with a 4.9% interest rate is $%7.2f %n", balance);
System.out.printf("Your balance after two years with a 4.9% interest rate is $%7.2f %n", secondYearBalance);
System.out.println();
}

The % symbol is used in a printf string for 'put a variable here'.
That's problematic when you write 4.9% interest rate because java thinks that % i is you saying: "a variable goes here". The fix is trivial; a double % is how you write a single percent. Thus:
System.out.printf("Your balance after one year with a 4.9%% interest rate is $%7.2f %n", balance);

Formatting percentages with printf

import java.util.Scanner;
public class Taxes {
public static void main(String[] args) {
// TODO Auto-generated method stub
System.out.printf("Enter the employees first name: ");
Scanner input = new Scanner(System.in);
String fName = input.nextLine();
System.out.printf("Enter the employees last name: ");
String lName = input.nextLine();
System.out.printf("Enter the hours worked for the week: ");
double hours = input.nextDouble();
System.out.printf("Enter the hourly pay rate: ");
double pay = input.nextDouble();
double gross = hours * pay;
System.out.printf("Enter the federal tax withholding: ");
double fed = input.nextDouble();
double fTax = gross * fed;
System.out.printf("Enter the state tax withholding: ");
double state = input.nextDouble();
double sTax = gross * state;
double Ttax = sTax + fTax;
double net = gross - Ttax;
System.out.printf(
"Employee Name:%s %s\n\nHours Worked:%s hours\n\nPay Rate:$%.2f\n\nGross pay:$%.2f\n\nDeductions: \n\n\tFederal Withholding:(%.2f%%)$%.2f \n\n"
+ "\tState Withholding:(%.2f%%)$%.2f\n\n\tTotal Witholding:$%.2f\n\nNet Pay:$%.2f",
fName, lName, hours, pay, gross, fed, fTax, state, sTax, Ttax, net);
input.close();
}
}
I need to declare two more variables to get the Federal and State tax withholdings to show as a percent.
Example They show as (00.20%) I need them to return as a whole percent like (20.00%)
I've tried declaring new variable at the bottom such as:
statewit = sTax * 100;
fedwit = fTax * 100;
to get the percents to return as I want but it tends to add that total to the net at the end.
Any help would be appreciated greatly, thanks!

Try this.
double percent=12.34;
System.out.printf("%.2f%%", percent);
// or in different convention "percent as number *100"
System.out.printf("%.2f%%", percent*100.0);
EDIT: Your Question can be divided in two:
Convention in which numbers are used (normal or percent scaled *100)
Real formatting to String
BTW Your code is long and has very little to FORMATTING.
Java has no special type for percent values. Types: double, BigDecimal can be used with his behaviour, or integer types too, if programmer keep integer convention
EDIT: thanks Costis Aivalis , comma corrected :)

Is this the correct syntax for inputing a string to an if statement or am i completely off?

package travelCost;
import java.util.Scanner;
public class travelCost {
public static void main(String[] args) {
//Scanner function
Scanner in = new Scanner(System.in);
//define problem variables
//first
double distance;
double mpg;
double pricePerGallon;
double milesPerKwh;
double pricePerKwh;
double totalCostGas;
double totalCostElec;
String type;
//Here i want the user to input a string and then based upon the answer //section into the for loop
System.out.println("Enter whether the car is 'elec' or 'gas': ");
type = in.next();
if (type.equals("elec"))
{
System.out.println("Enter the Total Distance in Miles: ");
distance = in.nextDouble();
System.out.println("Enter the total Miles per Kwh: ");
milesPerKwh = in.nextDouble();
System.out.println("Enter the Total Price per Kwh: ");
pricePerKwh = in.nextDouble();
totalCostElec = (distance/milesPerKwh) * pricePerKwh;
System.out.printf("The trip is going to cost $%5.2f: ", totalCostElec);
} else if (type.equals("gas: ")
{
System.out.println("Enter the Miles per Gallon: ");
mpg = in.nextDouble();
System.out.println("Enter the total Price per Gallon of Gasoline: ");
pricePerGallon = in.nextDouble();
System.out.println("Enter the total Price per Gallon of Gasoline: ");
pricePerGallon = in.nextDouble();
totalCostGas = (distance/mpg) * pricePerGallon;
System.out.printf("The trip is going to cost $%5.2f", totalCostGas);
}else
{
System.out.println("Please resubmit entry");
}
System.out.println();
}
}

After the corrections which mentioned by Paul, here is the complete code:
travelCost.java
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
double distance;
double mpg;
double pricePerGallon;
double milesPerKwh;
double pricePerKwh;
double totalCostGas;
double totalCostElec;
String type;
System.out.println("Enter whether the car is 'elec' or 'gas': ");
type = in.next();
if (type.equals("elec")) {
System.out.println("Enter the Total Distance in Miles: ");
distance = in.nextDouble();
System.out.println("Enter the total Miles per Kwh: ");
milesPerKwh = in.nextDouble();
System.out.println("Enter the Total Price per Kwh: ");
pricePerKwh = in.nextDouble();
totalCostElec = (distance / milesPerKwh) * pricePerKwh;
System.out.printf("The trip is going to cost $%5.2f: ",
totalCostElec);
} else if (type.equals("gas")) {
System.out.println("Enter the Total Distance in Miles: ");
distance = in.nextDouble();
System.out.println("Enter the Miles per Gallon: ");
mpg = in.nextDouble();
System.out
.println("Enter the total Price per Gallon of Gasoline: ");
pricePerGallon = in.nextDouble();
System.out
.println("Enter the total Price per Gallon of Gasoline: ");
pricePerGallon = in.nextDouble();
totalCostGas = (distance / mpg) * pricePerGallon;
System.out.printf("The trip is going to cost $%5.2f", totalCostGas);
} else {
System.out.println("Please resubmit entry");
}
System.out.println();
}
Input:
elec 100 10 2
Output:
The trip is going to cost $20.00:

make it
else if (type.equals("gas"))

There are 4 problems with this:
The line } else if (type.equals("gas: ") needs another ) at the end.
In the "gas" case, you are using the variable distance but you do not give it a value.
While if (type.equals("elec")) is the correct syntax (answering your question), it is usually better to write if ("elec".equals(type)) because this will not throw a NullPointerException if type == null.
It should be "gas", not "gas: ".

As Paul mentions, your if statement syntax is correct, but it is good practice to start with the hard coded strings ("elec" and "gas") in order to avoid NullPointerExceptions. As mentioned in the other answers, the if else should be using "gas" instead of "gas: ". To help avoid those kinds of errors, you might consider making "elec" and "gas" into static final String constants. If you use constants, you'll know that they are the same throughout your program. You might also want to call type.toLowerCase() in the event that the user enters the response in uppercase.

Keep adding two numbers until the input is not a double type

I am trying to make a simple calculator program where a user enters two values, the method add() is called from the Operations class and the values are added and the result is displayed. And then I am using a do while loop in which the user keeps entering values which are added to the last total and the result is displayed. It has to keep running unless the user enters some input which is not of the type double.
import java.util.Scanner;
public class App {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.println("Enter the first number: ");
double number = input.nextDouble();
System.out.println("Enter the second number: ");
double number2 = input.nextDouble();
double total = Operations.add(number, number2);
System.out.println(total);
System.out.println("Enter the number again: );
number2 = input.nextDouble();
do {
total = Operations.add(total, number2);
System.out.println(total);
System.out.println("Enter the number again: ");
number2 = input.nextDouble();
} while (input.hasNextDouble());
System.out.println("Exit.");
}
}
And here is the Operations class
public class Operations {
public static double add(double n1, double n2) {
return n1 + n2;
}
}
It adds the first two values, and displays the result. Then it asks for the value again, user inputs, and it displays the result. But from here on there is a problem somewhere which I have tried so hard to figure out but couldn't do so. So please look over my code and tell me where the problem is. Its something in the do while loop which I am doing wrong.
Output:
Enter the first number:
5
Enter the second number:
2
7.0
Enter the number again:
1
8.0
Enter the number again please:
2
Here the program is running but does nothing when I press 2. If for example I press 6 again, it will still add 2 (which I entered before) to the total and display that
6
10.0
Enter the number again please:

Your issue lies with the order in which things are occurring. You want to prompt and input at the beginning of the do-while:
do {
System.out.println("Enter the number again: ");
number2 = input.nextDouble();
total = Operations.add(total, number2);
System.out.println(total);
} while (input.hasNextDouble());
This makes the first re-prompt and re-input redundant, so your final class looks like:
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.println("Enter the first number: ");
double number = input.nextDouble();
System.out.println("Enter the second number: ");
double number2 = input.nextDouble();
double total = Operations.add(number, number2);
System.out.println(total);
do {
System.out.println("Enter the number again: ");
number2 = input.nextDouble();
total = Operations.add(total, number2);
System.out.println(total);
} while (input.hasNextDouble());
System.out.println("Exit.");
}

Am I doing something wrong with my try-catch block?

So we have to make a mortgage calculation project where we have to ask the user to calculate again and now we have to make it so it prints out a error message every time the user enters a string value for any of the inputs. I thought I did it right but something strange happens every time I run it and I can't figure out why and I know it's something wrong with the Try-Catch blocks.
Here are my outputs: http://imgur.com/cbvwM5v
As you can see the third time i run the program I enter a "two" as the second input and it still did the calculations. Then, the third time I tried it, I entered a negative number then a "two" and everything worked the way I wanted it to. Then, the last time I ran it I put a positive number for the first input and it still did the calculations, anything you guys see that might be doing this? Also, I think I may have used the wrong exception, I'm not uite sure what it means, I just guessed. am I supposed to user NumberFormatException and there is also a line under nfe saying that the value is not being used.
Here's my code:
package MortgageCalculation2c;
import java.text.NumberFormat;
import java.util.Scanner;
/**
*
* #author Akira
*/
public class MortgageCalculation2c {
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
double loanAmount = 0;
double interestRate = 0;
double numberYears = 0;
double months;
double monthlyPayment;
double numerator;
double denominator;
double formula;
boolean userInput = true;
String answer = ("y");
while (userInput) {
try {
loanAmount = 0;
interestRate = 0;
numberYears = 0;
//prompt user for the loan amount
System.out.print("Enter the loan amount: ");
loanAmount = Double.parseDouble(in.nextLine());
//prompt the user for the interest rate
System.out.print("Enter the rate: ");
interestRate = Double.parseDouble(in.nextLine());
//prompt the user for thenumber of years
System.out.print("Enter the number of years: ");
numberYears = Double.parseDouble(in.nextLine());
} catch (NumberFormatException nfe) {
System.out.println("You must enter positive numerical data!");
}
//if the user enters a negative number print out a error message, if not, continue calculations
if ((loanAmount <= 0) || (interestRate <= 0) || (numberYears <= 0)) {
System.out.println("ALL NUMERICAL VALUES MUST BE POSITIVE!");
} else {
//convert the interest rate
interestRate = interestRate / 100 / 12;
//the number of years must be converted to months
months = numberYears * 12;
//numerator of the monthly payment formula
numerator = (Math.pow(1 + interestRate, months));
//denominator of the monthly payment formula
denominator = ((numerator)-1);
//the formula equals the numerator divided by the denominator
formula = ( numerator / denominator );
//monthly payment calculation
monthlyPayment = (interestRate * loanAmount * formula);
//sytem output
NumberFormat defaultFormat = NumberFormat.getCurrencyInstance();
System.out.println("The monthly payment is: " + defaultFormat.format(monthlyPayment));
}
//prompt the user if they would like to calculate the program again.
System.out.println("Would you like to calculate again (y/n) : ");
//if the user enters "y" the program will run again and if the user enters anything else it ends
answer = in.nextLine();
answer = answer.toLowerCase();
if ( answer.equals("y")){
userInput = true; //tests the program if it needs to run again
}else{
break; //ends the program
}
}
}
}
Is there anything that you guys can see that might be the problem?

It seems you need continue in your catch block, so the program flow goes back to the loop.
...
} catch (NumberFormatException nfe) {
System.out.println("You must enter positive numerical data!");
continue; // <---------- here
}
...
If this is not a specific exercise in try-catch construct, it be would be better to use Scanner's method hasNextDouble() for validatiing and nextDouble for reading and converting the numbers.
It will look something like this:
//prompt user for the loan amount
loanAmount = enterPositiveDouble("Enter the loan amount: ")
//prompt the user for the interest rate
interestRate = enterPositiveDouble("Enter the rate: ");
//prompt the user for the number of years
numberYears = enterPositiveDouble("Enter the number of years: ");
and you will have a special static method enterPositiveDouble like following:
static void enterPositiveDouble(String prompt) {
Scanner in = new Scanner(System.in);
boolean ok = true;
double result = -1;
do {
System.out.print(prompt);
ok = (in.HasNextDouble() && (result = in.NextDouble()) > 0)
if ! ok
System.out.println("You must enter positive numerical data!");
} while (!ok);
}
The above is not an optimal code but just the illustration of a possible solution.