A simplest hello.java program prints a lot of JNI warnings during bootstrap when run with -Xcheck:jni. This started happening this week.

cat hello.java 
public class hello {
  public static void main(String[] args) {
    System.out.println("hello");
  }
}

java -Xcheck:jni hello

JNI warnings printed on console are attached.

java -version
openjdk version "1.9.0-internal"
OpenJDK Runtime Environment (build 1.9.0-internal-akhil_2014_06_27_09_52-b00)
OpenJDK 64-Bit Server VM (build 1.9.0-internal-akhil_2014_06_27_09_52-b00, mixed mode)