While test generators have the potential to significantly reduce the costs of software testing and have the ability to increase the quality of the software tests (and thus, the software itself), they unfortunately have only limited support for testing object-oriented software and their underlying test generation techniques fail to scale up to software of industrial size and complexity. In this context, we developed JTestCraft, a state-of-the-art test generator for the Java programming that deals effectively with all object-oriented programming concepts, such as object array types, inheritance and polymorfism. Furthermore, JTestCraft can locate all relevant test cases due to the use of the novel Candidate Sequence Search algorithm. Other novel concepts introduced in this thesis include the Constraint Tree data-structure to improve scalability and the Heap Simulation Representation to simplify the implementation of the test generator. We evaluated JTestCraft by looking at its ability to generate tests that obtain high code coverage and compare the results to human crafted tests. In addition, the performance of JTestCraft is compared against similar tools. Finally, we give pointers for further research to improve the performance and usability of future test generators.