cold run:
	javac A.java B.java C.java D.java
	# outputs A.class B.class C.class D.class
	# also gives you:
	# A.java: A.java C.java lib/Foo.java lib2/Bar.java
	# B.java: B.java lib/Foo.java
	# C.java: C.java B.java
	# D.java: D.java

on the next run, lets assume lib/Foo.java and D.java changed
you need to run
	javac A.java B.java D.java
	# updates A.class B.class D.class
	# also gives updated dependency list
	# A.java: A.java C.java lib/Foo.java lib2/Bar.java lib/Qwe.java
	# B.java: B.java lib/Foo.java lib/Qwe.java
	# D.java: D.java lib/Foo2.java