I don't think the Java Sandbox has had significantly more security holes than other similar sandboxes (eg, Flash).
Most of these vulnerabilities are only applicable to environments which are required to run untrusted code.
It's not the language that has holes - it's the java plug-in runtime. I agree that this gives java a bad rep but it really isn't related to the language all that much for normal non-plug-in usage.
Writing good sandboxes can be hard. Web browsers are pretty good at it but unlike java - they dont also have to support unsandboxed code running on the same VM so that makes things considerably easier.
Why does Java have so many security holes? Is it really worse than any other language, or is it just so ubiquitous that it presents itself as a good target?