001 package org.hamcrest;
002
003 import org.hamcrest.internal.ReflectiveTypeFinder;
004
005
006 /**
007 * Convenient base class for Matchers that require a non-null value of a specific type
008 * and that will report why the received value has been rejected.
009 * This implements the null check, checks the type and then casts.
010 * To use, implement <pre>matchesSafely()</pre>.
011 *
012 * @param <T>
013 * @author Neil Dunn
014 * @author Nat Pryce
015 * @author Steve Freeman
016 */
017 public abstract class TypeSafeDiagnosingMatcher<T> extends BaseMatcher<T> {
018 private static final ReflectiveTypeFinder TYPE_FINDER = new ReflectiveTypeFinder("matchesSafely", 2, 0);
019 private final Class<?> expectedType;
020
021 /**
022 * Subclasses should implement this. The item will already have been checked
023 * for the specific type and will never be null.
024 */
025 protected abstract boolean matchesSafely(T item, Description mismatchDescription);
026
027 /**
028 * Use this constructor if the subclass that implements <code>matchesSafely</code>
029 * is <em>not</em> the class that binds <T> to a type.
030 * @param expectedType The expectedType of the actual value.
031 */
032 protected TypeSafeDiagnosingMatcher(Class<?> expectedType) {
033 this.expectedType = expectedType;
034 }
035
036 /**
037 * Use this constructor if the subclass that implements <code>matchesSafely</code>
038 * is <em>not</em> the class that binds <T> to a type.
039 * @param typeFinder A type finder to extract the type
040 */
041 protected TypeSafeDiagnosingMatcher(ReflectiveTypeFinder typeFinder) {
042 this.expectedType = typeFinder.findExpectedType(getClass());
043 }
044
045 /**
046 * The default constructor for simple sub types
047 */
048 protected TypeSafeDiagnosingMatcher() {
049 this(TYPE_FINDER);
050 }
051
052 @Override
053 @SuppressWarnings("unchecked")
054 public final boolean matches(Object item) {
055 return item != null
056 && expectedType.isInstance(item)
057 && matchesSafely((T) item, new Description.NullDescription());
058 }
059
060 @SuppressWarnings("unchecked")
061 @Override
062 public final void describeMismatch(Object item, Description mismatchDescription) {
063 if (item == null || !expectedType.isInstance(item)) {
064 super.describeMismatch(item, mismatchDescription);
065 } else {
066 matchesSafely((T) item, mismatchDescription);
067 }
068 }
069 }