1 files changed, 54 insertions, 0 deletions
diff --git a/hamcrest-core/src/main/java/org/hamcrest/FeatureMatcher.java b/hamcrest-core/src/main/java/org/hamcrest/FeatureMatcher.java
new file mode 100644
index 0000000..385cf99
--- /dev/null
+++ b/hamcrest-core/src/main/java/org/hamcrest/FeatureMatcher.java
@@ -0,0 +1,54 @@
+package org.hamcrest;
+
+import org.hamcrest.internal.ReflectiveTypeFinder;
+
+/**
+ * Supporting class for matching a feature of an object. Implement <code>featureValueOf()</code>
+ * in a subclass to pull out the feature to be matched against. 
+ *
+ * @param <T> The type of the object to be matched
+ * @param <U> The type of the feature to be matched
+ */
+public abstract class FeatureMatcher<T, U> extends TypeSafeDiagnosingMatcher<T> {
+  private static final ReflectiveTypeFinder TYPE_FINDER = new ReflectiveTypeFinder("featureValueOf", 1, 0); 
+  private final Matcher<? super U> subMatcher;
+  private final String featureDescription;
+  private final String featureName;
+  
+  /**
+   * Constructor
+   * @param subMatcher The matcher to apply to the feature
+   * @param featureDescription Descriptive text to use in describeTo
+   * @param featureName Identifying text for mismatch message
+   */
+  public FeatureMatcher(Matcher<? super U> subMatcher, String featureDescription, String featureName) {
+    super(TYPE_FINDER);
+    this.subMatcher = subMatcher;
+    this.featureDescription = featureDescription;
+    this.featureName = featureName;
+  }
+  
+  /**
+   * Implement this to extract the interesting feature.
+   * @param actual the target object
+   * @return the feature to be matched
+   */
+  protected abstract U featureValueOf(T actual);
+
+  @Override
+  protected boolean matchesSafely(T actual, Description mismatch) {
+    final U featureValue = featureValueOf(actual);
+    if (!subMatcher.matches(featureValue)) {
+      mismatch.appendText(featureName).appendText(" ");
+      subMatcher.describeMismatch(featureValue, mismatch);
+      return false;
+    }
+    return true;
+  }
+      
+  @Override
+  public final void describeTo(Description description) {
+    description.appendText(featureDescription).appendText(" ")
+               .appendDescriptionOf(subMatcher);
+  }
+}