Java has become the dominant language for teaching introductory computer science at both the high school and college levels. Yet Java's development tools and syntax often distract beginning students from the programming concepts being taught. To combat this problem, we have implemented DrJava, a pedagogic programming environment, and devised a sequence of language levels for Java, which partition the language into pieces that can be more easily taught at one time. DrJava is a lightweight, yet powerful, Java development environment suitable both for beginners and more advanced developers. The environment provides a simple interface based on a "read-eval-print loop" that enables a programmer to develop, test, and debug Java programs interactively and incrementally. DrJava is freely available under an open source license. This thesis describes DrJava and an implementation framework and conceptual design for language levels in Java.