Output Formatting

Output Formatting with DecimalFormat

Consider the following code segment.

Scanner sc = new Scanner (System.in);

int num_item = sc.nextInt();

double price_perunit = sc.nextDouble();

double charge = num_item * price_perunit;

System.out.println("Total price = "  + ": RM" + charge);

What is the output if num_item is 2 and price_perunit is 2.50?

Solution

Suppose we want the answer to be RM5.00 but the output we get is RM5.0. Why?

To correct the code, we need to use DecimalFormat class.    

The output statement should be like this;

 DecimalFormat myformat = new DecimalFormat("0.00");

System.out.println("Total price = "  + ": RM" + myformat.format(charge));

Try compile and run your program to see the output.

Note that to use DecimalFormat, you will need to add import java.text.DecimalFormat; at the top of your program, so that the compiler understands what you mean by it. If you forget this, you will get a compiler error ``cannot resolve symbol''.

import java.util.Scanner;

import java.text.DecimalFormat;

public class Price{

  public static void main(String[] args) {

  Scanner sc = new Scanner (System.in);

  int num_item = sc.nextInt();

  double price_perunit = sc.nextDouble();

  double charge = num_item * price_perunit;

  DecimalFormat myformat = new DecimalFormat("0.00");

  System.out.println("Total price = "  + ": RM" + myformat.format(charge));

  }

}

Output formatting Using printf

We can also use printf statement in Java programming. (printf is a C language keyword and usually used in C programming) . 

The printf method is part of the java.io.PrintStream class and provides String formatting similar to the printf() function in C.  

Example:

System.out.printf("Hello %s!%n", "World");

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The output from the above statement will be;

Hello World!

Line Separator

To break the string into separate lines, we have a %n specifier:

System.out.printf("baeldung%nline%nterminator");

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The code segment above will produce the following output:

baeldung

line

terminator

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The %n separator printf() will automatically insert the host system's native line separator.

Boolean Formatting

To format Boolean values, we use the %b format.

According to the docs, it works the following way: if the second argument is null, then the result is “false”. If the argument is a boolean or Boolean, then the result is the string returned by String.valueOf(arg). Otherwise, the result is “true”.

So, if we do the following:

System.out.printf("%b%n", null);

System.out.printf("%B%n", false);

System.out.printf("%B%n", 5.3);

System.out.printf("%b%n", "random text");

then we'll see: 

false

FALSE

TRUE

true 

String Formatting

To format a simple string, we'll use the %s combination. Additionally, we can make the string uppercase:

printf("'%s' %n", "java");

printf("'%S' %n", "java");opy

And this is the output:

'java' 

'JAVA'

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Also, to specify a minimum length, we can specify a width:

printf("'%15s' %n", "java");

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which gives us:

'       java'

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If we need to left-justify our string, we can use the – flag:

printf("'%-10s' %n", "java");Copy

and the output will be:

'java  '

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Even more, we can limit the number of characters in our output by specifying a precision:

System.out.printf("%2.2s", "Hi there!");

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The first x number in %x.ys syntax is the padding. y is the number of chars.

For our example here, the output is Hi.

Char Formatting

The result of %c is a Unicode character:

System.out.printf("%c%n", 's');

System.out.printf("%C%n", 's');

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The capital letter C will uppercase the result:

s

S

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But if we give it an invalid argument, then Formatter will throw IllegalFormatConversionException.

Number Formatting

Integer Formatting

printf also can be used to display the numerical datatype. However, it's only valid for certain data types. Here are some common ones:

• s formats strings.

• d formats decimal integers.

• f formats floating-point numbers.

• t formats date/time values.

Example:

System.out.println("1234567890123456789");

System.out.printf("%10d\n",56342);

System.out.printf("%3d\n", 56342);

The output: 

1234567890123456789

     56342

56342

The printf() method accepts all the integers available in the language — byte, short, int, long, and BigInteger if we use %d:

System.out.printf("simple integer: %d%n", 10000L);

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so, the output will be:

simple integer: 10000

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In case we need to format our number with the thousands separator, we can use the , flag. And we can also format our results for different locales:

System.out.printf(Locale.US, "%,d %n", 10000);

System.out.printf(Locale.ITALY, "%,d %n", 10000);

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As we can see, the formatting in the US is different than in Italy:

10,000 

10.000

Example to format a float number, we need to use character  f .

System.out.printf("%f", 5.1473);

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which will output:

5.147300

Of course, the first thing that comes to mind is to control the precision:

System.out.printf("'%5.2f'%n", 5.1473);

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Here we define the width of our number as 5, and the length of the decimal part is 2:

' 5.15'

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Here we have one-space padding from the beginning of the number to support the predefined width.

To have our output in scientific notation, we just use the e conversion-character:

System.out.printf("'%5.2e'%n", 5.1473);

And this is our result:

'5.15e+00' 

Example:

System.out.printf("To print integer number %d", 5);

System.out.printf("To print floating number %f", 5.0);

The output will be;

To print integer number 5To print floating number 5.000000

Example:

System.out.printf("To print integer number %d \n", 5);

System.out.printf("To print floating number %f", 5.0);

The output will be;

To print integer number 5

To print floating number 5.000000

Note: Use the 'next line' tab '\n' to separate the output into two different lines.

Example:

int a = 50;

System.out.printf("To print integer number %d \n", a);

System.out.printf("To print floating number with two decimal point, ");

System.out.printf("%.2f", 5.0);

The output will be;

To print integer number 50

To print floating number with two decimal point, 5.00

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Date and Time Formatting

For date and time formatting, the conversion string is a sequence of two characters: the t or T character and the conversion suffix.

Let's explore the most common time and date formatting suffix characters with examples.

Definitely, for more advanced formatting, we can use DateTimeFormatter, which has been available since Java 8.

Time Formatting

First, let's see the list of some useful suffix characters for time formatting:

• H, M, S characters are responsible for extracting the hours, minutes and seconds from the input Date.

• L, N represent the time in milliseconds and nanoseconds accordingly.

• p adds a.m./p.m. formatting.

• z prints out the time-zone offset.

Now, let's say we want to print out the time part of a Date:

Date date = new Date();

System.out.printf("%tT%n", date);

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The code above along with %tT combination produces the following output:

13:51:15

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In case we need more detailed formatting, we can call for different time segments:

System.out.printf("hours %tH: minutes %tM: seconds %tS%n", date, date, date);

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Having used H, M and S, we get this result:

hours 13: minutes 51: seconds 15

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However, listing date multiple times is a pain.

Alternatively, to get rid of multiple arguments, we can use the index reference of our input parameter, which is 1$ in our case:

System.out.printf("%1$tH:%1$tM:%1$tS %1$tp %1$tL %1$tN %1$tz %n", date);

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Here we want as an output the current time, a.m./p.m., the time in milliseconds and nanoseconds, and the time-zone offset:

13:51:15 pm 061 061000000 +0400

Date Formatting

Like time formatting, we have special formatting characters for date formatting:

• A prints out the full day of the week.

• d formats a two-digit day of the month.

• B is for the full month name.

• m formats a two-digit month.

• Y outputs a year in four digits.

• y outputs the last two digits of the year.

Suppose we want to show the day of the week, followed by the month:

System.out.printf("%1$tA, %1$tB %1$tY %n", date);

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Then, using A, B and Y, we'd get this output:

Thursday, November 2018

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To have our results all in numeric format, we can replace the A, B, Y letters with d, m, y:

System.out.printf("%1$td.%1$tm.%1$ty %n", date);

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which will result in:

22.11.18 

Exercise 

What would the following print out? 

DecimalFormat fmt1 = new DecimalFormat("0.000E0");   

DecimalFormat fmt2 = new DecimalFormat("0.0##");   

System.out.println ( fmt1.format(0.1) );           // (a)   System.out.println ( fmt1.format(3.14159) );       // (b)   System.out.println ( fmt2.format(1.5) );           // (c)   System.out.println ( fmt2.format(0.0009) );        // (d)   System.out.println ( fmt2.format(2.7e3) );         // (e) 

Note: Write a simple program to see the output. 

Your test program will need to import java.text.DecimalFormat.