Java Output Basics | Developer.com

Whatever programming language you work with, you likely have to accept input from an external source and produce output to be consumed by another program or end-user. Typically, the keyboard is the standard input device and the screen is the standard output device. As such, this programming tutorial will present a few useful methods for printing content to the screen in Java, including using the print() and println() methods.

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The print() and println() Methods in Java

The simplest way send output to the screen in Java is to use the print() or println() methods, or, more precisely, System.out.println() or System.out.print(), as both methods belong to the System class’s public static output field. As such, we never have to instantiate the System class in order to access its methods.

You have no doubt heard of the time-honored Hello World application. Here is what that looks like in Java:

class OutputExamples {
  public static void main(String[] args) {
  	
		System.out.print("Hello world!");   
  }
}

What’s the Difference Between print() and println()?

At this point you may be wondering why there are two methods to do the same thing. That is a fair question, and the reason is that println() adds an extra newline character, or character combination, so that the cursor appears on the following line. Here is an example to illustrate how to use println() in Java:

System.out.println("println #1");
System.out.println("println #2");

System.out.print("print #1 ");
System.out.print("print #2");
/* Outputs:
println #1
println #2
print #1 print #2
/*

How to Display Variables and Literals in Java

There are versions of both the print() and println() method for every native data type, wrapper class, and Objects too. In the case of native types, like int, or wrappers, like Double, these methods allow developers to print variables and literals without having to convert them to strings first. Here is some example code that prints a Double variable and int literal in Java, respectively:

Double monthlyAvg = 20.87;
System.out.println(monthlyAvg); //variable

System.out.println(99);         //literal
/* Outputs:
20.87
99
/*

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Using print() and println() with Objects

When the print() or println() method receives an object type that it does not recognize, it employs the class’s toString() method to convert it into a printable format. It is meant to be overridden by your class to print something meaningful. Otherwise, toString() formats the object in the default format. That is:

1. The name of the class
2. The “@” symbol
3. A hashcode of the object

Here’s is an example of how to use the toString() method in Java:

class MyClass {

}

class Main {
  public static void main(String[] args) {

    // create an object of the Test class
    MyClass myClass = new MyClass();

    // print the object
    System.out.println(myClass);
    // Outputs: [email protected]
  }
}

Here is another example:

class MyClass {
  static int myClassInstances = 0;
  
  MyClass() {
    myClassInstances++;         
  }
  
  @Override
    public String toString() {
      return "MyClass instance #" + myClassInstances;
  }
}

class Main {
  public static void main(String[] args) {

    // create an object of the Test class
    MyClass myClass = new MyClass();

    // print the object
    System.out.println(myClass);
    // Outputs: MyClass instance #1
  }
}

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How to Format Output in Java

Looking to have your output printed in a specific format? No problem, Java’s got you covered. For you coding veterans out there, remember the C language’s printf() function? As it happens, Java, which borrows liberally from C and C++, implements its own version of the popular function. Here are just a sampling of what printf() can do and how to format output in Java:

import java.lang.Math;

public class FormattedOutputUsingPrintf {  
  public static void main(String args[ ])  {  
    // printing a string value on the console  
    final String str = "Test string";  
    System.out.printf( "\nPrinting a String value: %s \n ", str );  
    // printing an int value on the console  
    final int anInt = 2112 ;  
    System.out.printf( "\nPrinting an int value: anInt = %d \n ", x );  
    // printing a decimal value on the console 
    int r = 5;   
    double area = Math.PI*(r*r);
    System.out.printf( "\nPrinting a decimal value: %f \n ", f );  
    // this formatting is used to specify the width to which the digits can extend  
    System.out.printf( "\nFormatting the output to specific width: area = %.4f \n ", f );  
    // this formatting will print it up to 2 decimal places  
    System.out.printf( "\nFormatted the output with precision: area = %.2f \n ", f );  
    // formats number from right margin and occupies a width of 20 characters  
    System.out.printf( "\nFormatted to right margin: area = %20.4f \n ", f );  
  }  
}  
/* Displays:
Printing a String value: Test string  
Printing an int value: anInt = 2112 
Printing a decimal value: 78.539816
Formatting the output to specific width: area = 78.5398 
Formatted the output with precision: area = 78.54 
Formatted to right margin: area = 78.5398 
*/

A Word aboout System.out.format() in Java

If you happen to run across the System.out.format() method, we did not skip it – it is an alias to printf() and does the exact same thing. Perhaps it is meant as an alternative for people who still have nightmares about C pointers.

For the full list of Java String format specifiers, take a look at the Java docs here.

How to Format Numbers Using the DecimalFormat Class

As you are no doubt aware, formatting numbers with decimals can be a challenge. To help with that, Java includes the DecimalFormat class. Here is some example code showing how to use DecimalFormat in Java:

import java.text.DecimalFormat;  

public class FormattedOutputUsingDecimalFormat {  
  public static void main( String args[ ] ) {  
    double myDouble = 123.4567;  
    // printing the number  
    System.out.printf( "\nThe number is: %f \n ", myDouble );      
    // printing only the numeric part of the floating number  
    DecimalFormat ft = new DecimalFormat( "####" );  
    System.out.println( "\nWithout fraction part the number is: " + ft.format( x ) );  
    // printing the number only up to 2 decimal places  
    ft = new DecimalFormat( "#.##" );  
    System.out.println( "\nFormatted number with the specified precision is: " + ft.format( x ) );  
    // to automatically appends zero to the rightmost decimal place, use 0 instead of #
    ft = new DecimalFormat( "#.000000" ) ;  
    System.out.println( "\nAppending the zeroes to the right of the number: " + ft.format( x ) );  
    // to automatically append zero to the leftmost decimal place, use 0 instead of #  
    ft = new DecimalFormat( "00000.00" ) ;  
    System.out.println( "\nAppending the zeroes to the left of the number: "+ ft.format( x ) );  
    // formatting money in dollars  
    double income = 100000.789;  
    ft = new DecimalFormat( "$###,###.##"  );  
    System.out.println( "\n Your income in dollars is: " + ft.format( income ) );  
  }  
}  
/* Displays:
The number is: 123.456700 
Without fraction part the number is: 123 
Formatted number with the specified precision is: 123.46 
Appending the zeroes to the right of the number: 123.456700 
Appending the zeroes to the left of the number: 00123.46 
Your income in dollars is: $100,000.79 
*/

Final Thoughts on Java Output Basics

This programming tutorial presented a few useful methods for printing content to the screen in Java. Whether you need to display a string, native data type, or Object, there is a method for every occasion.

If you enjoyed this Java tutorial, stay tuned. In the next one, we will be learning all about Java variables!