The thing is that "Java" is really two different entities: the language itself, and the massive class library that typically comes with it (some of which is necessary because it implements classes defined in the language like String). The Java compiler outputs bytecode which is run on the Java Virtual Machine (JVM). Dalvik is essentially a replacement for the JVM. It uses different bytecode, hence why you use a tool to translate Java bytecode files into Dalvik ones to run. Then you have the library, much of which is written in Java itself. Android includes a replacement for the Java library which follows (for the groups of classes it includes) the Java library API exactly. That replacement library's been compiled to Dalvik bytecode and is included in the system just like the Java library would be, so programs have automatic access to it. Were it not for classes like Object and String, you could have Java/Dalvik programs without having the library at all (just as you can have C programs without the C Standard Library).

Oracle tries to conflate the two, talking about the language and virtual machine as if they were the class library and vice versa. The two are related and tend to go together, but they're not the same entity even though they usually have the same name.

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