Do you mean a Java implementation of Linq? Or a Java ORM tool?

1- There is a library named Quaere, but I think it is not a full LINQ implementation because LINQ uses Lambda Expressions and generates inspection tree at runtime. You can use it and if you have a good experience with Quaere, discuss here.

2- If you mean an ORM tool for Java, you can use JPA (Java Persistence API) with one of its implementation (Hibernate, TopLink).