System.out.println() is used mostly to print messages to the console. However very few of us are actually aware of its working mechanism.
- System is a class defined in the java.lang package.
- out is an instance of PrintStream , which is a public and static member of the class System.
- As all instances of PrintStream class have a public method println(), hence we can invoke the same on out as well. We can assume System.out represents the standard Output Stream .
One interesting fact related to the above topic is, we can use System.out.println() to print messages to other sources too (and not just console) . However before doing so , we must reassign the standard output by using the following method of System class:
System.setOut(PrintStream p);
PrintStream can be used for character output to a text file. Below program creates the file A.txt and writes to the file using System.out.println(
// Java program to demonstrate redirection in System.out.println() import java.io.*; public class SystemFact { public static void main(String arr[]) throws FileNotFoundException { // Creating a File object that represents the disk file. PrintStream o = new PrintStream(new File("A.txt")); // Store current System.out before assigning a new value PrintStream console = System.out; // Assign o to output stream System.setOut(o); System.out.println("This will be written to the text file"); // Use stored value for output stream System.setOut(console); System.out.println("This will be written on the console!"); } } |
In very similar fashion we can use System.out.println() to write to a Socket’s OutputStream as well.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above
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