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!");
}
}