Working of System.out.println()

How does System.out.println internally works?

By looking at the Java statement we can easily infer that:

1. System is a class.
2. out is a static instance variable of a class which has a method println()

When and where is the out instantiated in System.out.println()?

When the JVM is initialised, the method initializeSystemClass() is called that does exactly what it's name says - it initialises the System class and sets the out variable. The initializeSystemClass() method actually calls another method to set the out variable - this method is called setOut().

Here is what the different pieces of System.out.println() actually look like:

class System{
  public static final PrintStream out;
  //  . . .
}

//the PrintStream class belongs to java.io package
class PrintStream{
  public void println();
  // . . .
}