1 files changed, 58 insertions, 0 deletions
diff --git a/library/src/org/hamcrest/TypeSafeMatcher.java b/library/src/org/hamcrest/TypeSafeMatcher.java
new file mode 100644
index 0000000..7f18fd3
--- /dev/null
+++ b/library/src/org/hamcrest/TypeSafeMatcher.java
@@ -0,0 +1,58 @@
+package org.hamcrest;
+
+import java.lang.reflect.Method;
+
+/**
+ * Convenient base class for Matchers that require a non-null value of a specific type.
+ * This simply implements the null check, checks the type and then casts.
+ *
+ * @author Joe Walnes
+ */
+public abstract class TypeSafeMatcher<T> extends BaseMatcher<T> {
+
+    private Class expectedType;
+
+    /**
+     * Subclasses should implement this. The item will already have been checked for
+     * the specific type and will never be null.
+     */
+    public abstract boolean matchesSafely(T item);
+
+    protected TypeSafeMatcher() {
+        expectedType = findExpectedType(getClass());
+    }
+    
+    private static Class<?> findExpectedType(Class<?> fromClass) {
+        for (Class<?> c = fromClass; c != Object.class; c = c.getSuperclass()) {
+            for (Method method : c.getDeclaredMethods()) {
+                if (isMatchesSafelyMethod(method)) {
+                    return method.getParameterTypes()[0];
+                }
+            }
+        }
+        
+        throw new Error("Cannot determine correct type for matchesSafely() method.");
+    }
+    
+    private static boolean isMatchesSafelyMethod(Method method) {
+        return method.getName().equals("matchesSafely") 
+            && method.getParameterTypes().length == 1
+            && !method.isSynthetic(); 
+    }
+    
+    protected TypeSafeMatcher(Class<T> expectedType) {
+    	this.expectedType = expectedType;
+    }
+
+    /**
+     * Method made final to prevent accidental override.
+     * If you need to override this, there's no point on extending TypeSafeMatcher.
+     * Instead, extend the {@link BaseMatcher}.
+     */
+    @SuppressWarnings({"unchecked"})
+    public final boolean matches(Object item) {
+        return item != null
+                && expectedType.isInstance(item)
+                && matchesSafely((T) item);
+    }
+}