Formatting Output in Java Part 1

Introduction

Java provides some built-in methods in its standard library that are useful to specify how we want to display the information on the console or in the User Graphical Interface. You can use the System.out.println() and System.out.print() standard methods described in the following code snippet to display information to the end-user:

public class PrintSomething {
    public static void main(String[] args) {
        short num1 = 65, num2 = 5, age = 34;
        String name = "Tom";
        System.out.println(num1 + " per " + num2 + " is " + num1 * num2);
        System.out.println(num1 + " per " + num2 + " is " + num1 * num2);
    }
}

Program Output:
65 per 5 is 325
Tom is 34 years!

This approach works fine!

public class FloatPointNumber {
    public static void main(String[] args) {
        double num1 = 14.5, num2 = 2.6;
         // This line is a bad idea!
        System.out.println(num1 + " / " + num2 + " = " + num1 / num2);
    }
}

Program Output:
14.5 / 2.6 = 5.576923076923077

Notice that the output shows an unrounded number with many decimal places. It is uneasy to read. Fortunately, there is an elegant way to solve the problem.

PrintStream class

You have been using the println() and print() methods to display the output of a program. Both are methods of the PrintStream class, which belongs to a package called Java.io¹ that contains some Classes related to input and output. PrintStream² also provides methods, such as format() and printf(), that are useful to specify how a value should be formatted.

format() returns a reference to the formatted string, so you must define a variable and store the referenced value in it. Then you can use the variable within the program. Instead, printf() prints the formatted string directly to the console.

That said, over here is the syntax that both share.

System.out.printf(FormatString, ArgumentList);
String.format(FormatString, ArgumentList);

Both methods admit two arguments. FormatString represents a string that includes one or more format specifiers with some optional text. It is a placeholder for the second argument and contains instructions on how it should be formatted. ArgumentList refers to any of the data types supported by Java. You can include one or more of them.

Conclusion

So far, we have briefly reviewed the PrintStream class of the Java programming language. The PrintStream class has two additional methods, printf() and format(). Both share similar arguments with which we can specify how to format a value. In the next post, we'll learn about the elements of the format specifier, along with their meanings.

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