Are you referring to the programming language, or the compiler and runtime environment necessary to execute the code? The Java Language Specification doesn't provide any strong guarantees of "safety". For example, it's certainly possible to write Java code with heap memory leaks or stack overflows. And I have run into multiple defects with the Oracle JVM that caused segfaults when executing certain code (although to Oracle's credit, their JVM is generally one of the highest quality and most reliable pieces of large platform software ever created).