This paper presents an ontology, the Java Learning Object Ontology - JLOO, for organizing learning objects of Java courses in an adaptive e-learning environment. The classification is based on the Computing Curricula CC2001 of the ACM and IEEE/CS. Using the curriculum as a guideline, the ontology defines the atomic knowledge units (i.e. learning objects) for an introductory course of Java programming. The most significant contributions of JLOO are: 1) defining the atomic knowledge units of introductory courses of Java language, and the relationships among them, 2) making the knowledge units of JLOO sharable and reusable, 3) allowing different learning strategies of a e-learning environment to choose dynamically, using JLOO as a guideline, different learning paths, and 4) making the realization of adaptive learning easy.