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diff --git a/src/main/java/org/apache/commons/math3/ode/sampling/FixedStepHandler.java b/src/main/java/org/apache/commons/math3/ode/sampling/FixedStepHandler.java
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.math3.ode.sampling;
+
+
+/**
+ * This interface represents a handler that should be called after
+ * each successful fixed step.
+
+ * <p>This interface should be implemented by anyone who is interested
+ * in getting the solution of an ordinary differential equation at
+ * fixed time steps. Objects implementing this interface should be
+ * wrapped within an instance of {@link StepNormalizer} that itself
+ * is used as the general {@link StepHandler} by the integrator. The
+ * {@link StepNormalizer} object is called according to the integrator
+ * internal algorithms and it calls objects implementing this
+ * interface as necessary at fixed time steps.</p>
+ *
+ * @see StepHandler
+ * @see StepNormalizer
+ * @since 1.2
+ */
+
+public interface FixedStepHandler  {
+
+  /** Initialize step handler at the start of an ODE integration.
+   * <p>
+   * This method is called once at the start of the integration. It
+   * may be used by the step handler to initialize some internal data
+   * if needed.
+   * </p>
+   * @param t0 start value of the independent <i>time</i> variable
+   * @param y0 array containing the start value of the state vector
+   * @param t target time for the integration
+   */
+  void init(double t0, double[] y0, double t);
+
+  /**
+   * Handle the last accepted step
+   * @param t time of the current step
+   * @param y state vector at t. For efficiency purposes, the {@link
+   * StepNormalizer} class reuses the same array on each call, so if
+   * the instance wants to keep it across all calls (for example to
+   * provide at the end of the integration a complete array of all
+   * steps), it should build a local copy store this copy.
+   * @param yDot derivatives of the state vector state vector at t.
+   * For efficiency purposes, the {@link StepNormalizer} class reuses
+   * the same array on each call, so if
+   * the instance wants to keep it across all calls (for example to
+   * provide at the end of the integration a complete array of all
+   * steps), it should build a local copy store this copy.
+   * @param isLast true if the step is the last one
+   */
+  void handleStep(double t, double[] y, double[] yDot, boolean isLast);
+
+}