PrintStream object out is initialized by null, how we call method on it?

Question

I have seen in the System class that the out object (of type PrintStream) is initialized with a null value. How can we call method like System.out.prinln("");? In System class out variable initialized like this way:

package java.lang;

public final class System {
    public final static PrintStream out = nullPrintStream();

     private static PrintStream nullPrintStream() throws NullPointerException {
        if (currentTimeMillis() > 0) {
            return null;
        }
        throw new NullPointerException();
     }
}

As per shown above code out variable initialized by null and this variable is final, so it can not initialized further then how can we use "out" variable.

Answer 1

JVM calls the private static void initializeSystemClass() method which initializes it.

See these two lines of code :

setOut0(new PrintStream(new BufferedOutputStream(fdOut, 128), true));
setErr0(new PrintStream(new BufferedOutputStream(fdErr, 128), true));

These are the two native methods :

private static native void setOut0(PrintStream out);
private static native void setErr0(PrintStream err);

There is a nice article on it.