Here are some of the promises the Java virtual machine makes about programs that have passed the verification algorithm:
The Java platform security architecture depends on all these promises and many more. The verification algorithm, which enforces these promises, was outlined in chapter 6. A more complete description is available in The Java Virtual Machine Specification, chapter 4. You can check the algorithms out for yourself. Part of the strength of the Java platform security architecture lies in the fact that many independent reviewers have checked the algorithms.