Consider code like:
---
public class Test {
     private List<String> l = new ArrayList<String>();
}
---

Running javac with -XDfind=diamond will not produce a warning about the diamond candidate, while doing the some on:
---
public class Test {
     List<String> l = new ArrayList<String>();
}
---

will produce:
Test.java:4: warning: Redundant type arguments in new expression (use diamond operator instead).
     List<String> l = new ArrayList<String>();
                                   ^
1 warning