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import java.io.*;
import java.util.SortedMap;
import org.checkerframework.checker.nullness.qual.*;
import org.checkerframework.checker.nullness.qual.EnsuresNonNullIf;
public class NonEmptyCollection {
public static @NonNull String returnRemove(@NonNull PriorityQueue1<@NonNull String> pq) {
return pq.remove();
}
public static @NonNull String returnPoll1(PriorityQueue1<@NonNull String> pq) {
// :: error: (return.type.incompatible)
return pq.poll();
}
public static @NonNull String returnPoll2(PriorityQueue1<@NonNull String> pq) {
if (pq.isEmpty()) {
return "hello";
} else {
return pq.poll();
}
}
public static @NonNull String returnFirstKey(SortedMap<String, String> sm) {
return sm.firstKey();
}
///////////////////////////////////////////////////////////////////////////
/// Helper classes copied from JDK
///
public class PriorityQueue1<E> {
@SuppressWarnings("purity") // object creation is forbidden in pure methods
@org.checkerframework.dataflow.qual.Pure
public @Nullable E poll() {
throw new RuntimeException("skeleton method");
}
public E remove() {
throw new RuntimeException("skeleton method");
}
@EnsuresNonNullIf(result = false, expression = "poll()")
public boolean isEmpty() {
throw new RuntimeException("skeleton method");
}
}
}
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