Extract various constants in DefaultKeyGenerator

org.springframework.context/src/main/java/org/springframework/cache/interceptor/DefaultKeyGenerator.java

@@ -21,25 +21,30 @@ import java.lang.reflect.Method;
 import org.springframework.cache.interceptor.KeyGenerator;
 
 /**
- * Default key generator. Returns 0 if no param is given, the param itself if
- * only one is given or a hash code computed from all given params hash code.
- * Uses a constant (53) for <code>null</code> objects.
+ * Default key generator. Returns {@value #NO_PARAM_KEY} if no parameters are provided,
+ * the parameter itself if only one is given or a hash code computed from all given
+ * parameters' hash code values. Uses the constant value {@value #NULL_PARAM_KEY} for any
+ * {@code null} parameters given.
  *
  * @author Costin Leau
+ * @author Chris Beams
  * @since 3.1
  */
 public class DefaultKeyGenerator implements KeyGenerator {
 
+	public static final int NO_PARAM_KEY = 0;
+	public static final int NULL_PARAM_KEY = 53;
+
 	public Object extract(Object target, Method method, Object... params) {
 		if (params.length == 1) {
-			return (params[0] == null ? 53 : params[0]);
+			return (params[0] == null ? NULL_PARAM_KEY : params[0]);
 		}
 		if (params.length == 0) {
-			return 0;
+			return NO_PARAM_KEY;
 		}
 		int hashCode = 17;
 		for (Object object : params) {
-			hashCode = 31 * hashCode + (object == null ? 53 : object.hashCode());
+			hashCode = 31 * hashCode + (object == null ? NULL_PARAM_KEY : object.hashCode());
 		}
 		return Integer.valueOf(hashCode);
 	}