001    package ps2;
002    
003    import java.util.*;
004    
005    /**
006     * This class illustrates use of nullness type annotations.
007     * The class doesn't do anything -- it is merely meant to be compiled.
008     * Compilation will produce warning messages.
009     * <p>
010     *
011     * There are two related files that differ only slightly:
012     * {@link NullnessExample}, an example of correct use, and {@link
013     * NullnessExampleWithWarnings}, an example of incorrect use.
014     * See the Nullness checker documentation for larger examples of annotated code.
015     **/
016    public class NullnessExampleWithWarnings {
017    
018      public void example() {
019    
020        // In general, you do not have to annotate local variables, because the
021        // Nullness Checker infers such annotations.  It is written here in the
022        // example for emhpasis.
023        /*@NonNull*/ String foo = "foo";
024        String bar = null;
025    
026        foo = bar;
027        bar = foo;
028    
029      }
030    
031      public /*@NonNull*/ String exampleGenerics() {
032    
033        List</*@NonNull*/ String> foo = new LinkedList</*@NonNull*/ String>();
034        List<String> bar = foo;
035    
036        String quux = null;
037        foo.add(quux);
038        foo.add("quux");
039        /*@NonNull*/ String baz = foo.get(0);
040        return baz;
041    
042      }
043    
044    }