You need to have in mind that programming Java for Android isn't the same that programming Java for desktop. Language is more or less the same but the classes that you use might be quite different here and there.
Second link you posted is "official" documentation about the language. Oracle its the company that owns Java (which isn't the same Java that Android has). So whatever you find there you can be sure that it works like it says it does.
It has a couple of beginner friendly tutorials and other tutorials that are more tailored for "Ok, I know Java, I just want to know how feature XYZ is used.". So you'll find varied information there.
Moreover, always consult the javadocs for the standard library. All methods and classes in the standard library are documented. By default (on all popular IDEs like Eclipse or Netbeans), when you hover over some standard library method/class, you get a pop up with the javadoc for that method/class. Read those, they'll help you a lot. Coding in the dark (ie, without docs) isn't much fun when you just want to learn.
You can also consult javadocs online too, for example, java.lang.Object javadocs.