如何使用 System.out.printf() 将数字的 output 显示到小数点后两位？

Question

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();
}

Answer 1

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);