diff --git a/history/004_seasaw/src/main/java/com/github/drinkjava2/frog/brain/Zone.java b/history/004_seasaw/src/main/java/com/github/drinkjava2/frog/brain/Zone.java
new file mode 100644
index 0000000..d8ae70e
--- /dev/null
+++ b/history/004_seasaw/src/main/java/com/github/drinkjava2/frog/brain/Zone.java
@@ -0,0 +1,84 @@
+/*
+ * Copyright 2018 the original author or authors. 
+ * Licensed 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 com.github.drinkjava2.frog.brain;
+
+import java.io.Serializable;
+
+import com.github.drinkjava2.frog.Env;
+
+/**
+ * Zone represents a rectangle zone in brain
+ * 
+ * @author Yong Zhu
+ * @since 1.0
+ */
+public class Zone implements Serializable {
+	private static final long serialVersionUID = 1L;
+
+	public float x;
+	public float y;
+	public float r;// r为这个矩形区边长的一半
+
+	public Zone() {
+		// 空构造器不能省
+	}
+
+	public Zone(float x, float y, float r) {// 用x,y,r来构造
+		this.x = x;
+		this.y = y;
+		this.r = r;
+		if (this.x < 0)
+			this.x = 0;
+		if (this.y < 0)
+			this.y = 0;
+		if (this.x > Env.FROG_BRAIN_WIDTH)
+			this.x = Env.FROG_BRAIN_WIDTH;
+		if (this.y > Env.FROG_BRAIN_WIDTH)
+			this.y = Env.FROG_BRAIN_WIDTH;
+	}
+
+	public Zone(Zone z) {// 用另一个Zone来构造
+		this.x = z.x;
+		this.y = z.y;
+		this.r = z.r;
+	}
+
+	public boolean nearby(Zone z) {
+		float dist = r + z.r;
+		return (Math.abs(x - z.x) < dist && Math.abs(y - z.y) < dist);
+	}
+
+	public int roundX() {
+		return Math.round(x);
+	}
+
+	public int roundY() {
+		return Math.round(y);
+	}
+
+	public static void copyXY(Zone from, Zone to) {
+		to.x = from.x;
+		to.y = from.y;
+	}
+
+	public static void copyXYR(Zone from, Zone to) {
+		to.x = from.x;
+		to.y = from.y;
+		to.r = from.r;
+	}
+
+	public void setXYR(float x, float y, float r) {
+		this.x = x;
+		this.y = y;
+		this.r = r;
+	}
+
+}