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) {
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);

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;

public final void describeTo(Description description) {
description.appendText(featureDescription).appendText(" ")