Java Puzzle 21 (What does this program output?)

Puzzle21.java

import java.io.ByteArrayOutputStream;
import java.io.PrintStream;

public class Puzzle21 {

	public static void main(String[] args) {
		ByteArrayOutputStream bytes = new ByteArrayOutputStream();
		PrintStream oldStream = System.out;
		PrintStream newStream = new PrintStream(bytes);
		System.setOut(newStream);
		System.setErr(newStream);
		System.out.print(0 + "_" + 0);
		System.out.print(0_0);
		System.out.print(0_0_0);
		System.out.print(0_0_0L);
		System.out.print(0_0_0.0F);
		String string = new String(bytes.toByteArray());
		System.setOut(oldStream);
		try {
			System.out.println(Double.parseDouble(string));
		} catch (Throwable t) {
			t.printStackTrace();
		}
		System.out.println("Cool.");
	}
	
}