Annotations on type use - Using #java8 annotations and "checker framework"

NullCast.java

import org.checkerframework.checker.nullness.qual.*;

/**
 * Before Java SE 8 annotations could only be applied to declarations.
 * With Java SE 8+, annotations can also be applied to any type use.
 *
 * See: http://docs.oracle.com/javase/tutorial/java/annotations/type_annotations.html
 *
 * To compile this sample:
 *
 * 1) Download "checker framework" from 
 *    http://types.cs.washington.edu/checker-framework/current/checker-framework.zip
 *    I used version 1.8.10
 *
 * 2) Expand check-framework.zip under say $CHECKER_FRAMEWORK directory
 *
 * 3) $CHECKER_FRAMEWORK/checker/bin/javac -processor NullnessChecker NullCast.java
 *
 * You should see this warning:
 *
<pre>
NullCast.java:35: warning: [cast.unsafe] "@Initialized @Nullable Object" may not be casted to the type "@Initialized @NonNull String"
      String s = (@NonNull String)arg;
                 ^
1 warning
</pre>
 *
 */
public class NullCast {
   public void main(@Nullable Object arg) {
      // if you uncomment this null check "if" statement then
      // the warning will disappear as the cast is after null check.

      // if (arg != null) {
      String s = (@NonNull String)arg;
      System.out.println(s);
      // }
   }
}