diff --git a/history/005a1_letter_test/src/main/java/com/gitee/drinkjava2/frog/Frog.java b/history/005a1_letter_test/src/main/java/com/gitee/drinkjava2/frog/Frog.java
new file mode 100644
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+++ b/history/005a1_letter_test/src/main/java/com/gitee/drinkjava2/frog/Frog.java
@@ -0,0 +1,222 @@
+/*
+ * 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.gitee.drinkjava2.frog;
+
+import java.awt.Graphics;
+import java.awt.Image;
+import java.io.FileInputStream;
+import java.util.ArrayList;
+import java.util.List;
+
+import javax.imageio.ImageIO;
+
+import com.gitee.drinkjava2.frog.brain.Cell;
+import com.gitee.drinkjava2.frog.brain.CellActions;
+import com.gitee.drinkjava2.frog.brain.Cuboid;
+import com.gitee.drinkjava2.frog.brain.Hole;
+import com.gitee.drinkjava2.frog.brain.Organ;
+import com.gitee.drinkjava2.frog.brain.Photon;
+import com.gitee.drinkjava2.frog.egg.Egg;
+import com.gitee.drinkjava2.frog.objects.Material;
+
+/**
+ * Frog = cells <br/>
+ * cells = actions + photons <br/>
+ * 
+ * Frog's name is Sam.
+ * 
+ * 青蛙脑由一个cells三维数组组成，每个cell里可以存在多个行为，行为是由器官决定，同一个细胞可以存在多种行为。光子是信息的载体，永远不停留。
+ * 
+ * @author Yong Zhu
+ * @since 1.0
+ */
+public class Frog {// 这个程序大量用到public变量而不是getter/setter，主要是为了编程方便和简洁，但缺点是编程者需要小心维护各个变量
+	/** brain cells */
+	public Cell[][][] cells;// 一开始不要初始化，只在调用getOrCreateCell方法时才初始化相关维以节约内存
+
+	/** organs */
+	public List<Organ> organs = new ArrayList<>();
+
+	public int x; // frog在Env中的x坐标
+	public int y; // frog在Env中的y坐标
+	public long energy = 10000000; // 青蛙的能量为0则死掉
+	public boolean alive = true; // 设为false表示青蛙死掉了，将不参与计算和显示，以节省时间
+	public int ateFood = 0;
+
+	static Image frogImg;
+	static {
+		try {
+			frogImg = ImageIO.read(new FileInputStream(Application.CLASSPATH + "frog.png"));
+		} catch (Exception e) {
+			e.printStackTrace();
+		}
+	}
+
+	public Frog(int x, int y, Egg egg) {// x, y 是虑拟环境的坐标
+		this.x = x;
+		this.y = y;
+		for (Organ org : egg.organs)
+			organs.add(org);
+	}
+
+	public void initFrog() {// 仅在测试之前调用这个方法初始化frog以节约内存，测试完成后要清空units释放内存
+		try {
+			cells = new Cell[Env.FROG_BRAIN_XSIZE][][]; // 为了节约内存，先只初始化三维数组的x维，另两维用到时再分配
+		} catch (OutOfMemoryError e) {
+			System.out.println("OutOfMemoryError found for frog, force it die.");
+			this.alive = false;
+			return;
+		}
+		for (int orgNo = 0; orgNo < organs.size(); orgNo++) {
+			organs.get(orgNo).init(this, orgNo);
+		}
+	}
+
+	/** Find a organ in frog by organ's name */
+	@SuppressWarnings("unchecked")
+	public <T extends Organ> T findOrganByName(String organName) {// 根据器官名寻找器官，但不是每个器官都有名字
+		for (Organ o : organs)
+			if (o.organName != null && organName.equalsIgnoreCase(o.organName))
+				return (T) o;
+		return null;
+	}
+
+	/** Set with given activeValue */
+	public void setCuboidVales(Cuboid o, boolean active) {// 激活长方体区域内的所有脑区
+		if (!alive)
+			return;
+		for (int x = o.x; x < o.x + o.xe; x++)
+			if (cells[x] != null)
+				for (int y = o.y; y < o.y + o.ye; y++)
+					if (cells[x][y] != null)
+						for (int z = o.z; z < o.z + o.ze; z++)
+							if (cells[x][y][z] != null)
+								getOrCreateCell(x, y, z).hasInput = active;
+	}
+
+	private int activeNo = 0;// 每一帧光子只能走一步，用这个来作标记
+
+	public boolean active(Env v) {// 这个active方法在每一步循环都会被调用，是脑思考的最小帧
+		activeNo++;
+		// 如果能量小于0、出界、与非食物的点重合则判死
+		if (!alive || energy < 0 || Env.outsideEnv(x, y) || Env.bricks[x][y] >= Material.KILLFROG) {
+			energy -= 100; // 死掉的青蛙也要消耗能量，确保淘汰出局
+			alive = false;
+			return false;
+		}
+		energy -= 20;
+		for (Organ o : organs)
+			o.active(this); // 调用每个器官的active方法， 通常只用于执行器官的外界信息输入、动作输出，脑细胞的遍历不是在这一步
+
+		// 这里是最关键的脑细胞主循环，脑细胞负责捕获和发送光子，光子则沿它的矢量方向每次自动走一格，如果下一格是真空(即cell未初始化）会继续走下去并衰减直到为0(为减少运算)
+		for (int i = 0; i < Env.FROG_BRAIN_XSIZE; i++) {
+			Env.checkIfPause(this);
+			if (cells[i] != null)
+				for (int j = 0; j < Env.FROG_BRAIN_YSIZE; j++)
+					if (cells[i][j] != null)
+						for (int k = 0; k < Env.FROG_BRAIN_ZSIZE; k++) {
+							Cell cell = cells[i][j][k];
+							if (cell != null)
+								CellActions.act(this, activeNo, cell); // 调用每个细胞的act方法
+						}
+		}
+		return alive;
+	}
+
+	public void show(Graphics g) {// 显示青蛙的图象
+		if (!alive)
+			return;
+		g.drawImage(frogImg, x - 8, y - 8, 16, 16, null);
+	}
+
+	/** Check if cell exist */
+	public Cell getCell(int x, int y, int z) {// 返回指定脑ssf坐标的cell ，如果不存在，返回null
+		if (cells[x] == null || cells[x][y] == null)
+			return null;
+		return cells[x][y][z];
+	}
+
+	/** Get a cell in position (x,y,z), if not exist, create a new one */
+	public Cell getOrCreateCell(int x, int y, int z) {// 获取指定坐标的Cell，如果为空，则在指定位置新建Cell
+		if (outBrainBound(x, y, z))
+			return null;
+		if (cells[x] == null)
+			cells[x] = new Cell[Env.FROG_BRAIN_YSIZE][];
+		if (cells[x][y] == null)
+			cells[x][y] = new Cell[Env.FROG_BRAIN_ZSIZE];
+		Cell cell = cells[x][y][z];
+		if (cell == null) {
+			cell = new Cell(x, y, z);
+			cells[x][y][z] = cell;
+		}
+		return cell;
+	}
+
+	/** Check if x,y,z out of frog's brain bound */
+	public static boolean outBrainBound(int x, int y, int z) {// 检查指定坐标是否超出frog脑空间界限
+		return x < 0 || x >= Env.FROG_BRAIN_XSIZE || y < 0 || y >= Env.FROG_BRAIN_YSIZE || z < 0
+				|| z >= Env.FROG_BRAIN_ZSIZE;
+	}
+
+	/** Photon always walk */
+	public void addAndWalk(Photon p) { // 添加光子的同时让它沿光子方向自动走一格
+		p.x += p.mx;
+		p.y += p.my;
+		p.z += p.mz;
+		int rx = Math.round(p.x);
+		int ry = Math.round(p.y);
+		int rz = Math.round(p.z);
+		if (Frog.outBrainBound(rx, ry, rz))
+			return;// 出界直接扔掉
+		Cell cell = getCell(rx, ry, rz);
+		if (cell != null)
+			cell.addPhoton(p);
+	}
+
+	/** Photon always walk */
+	public void addAndWalkAndDig(Photon p) { // 添加光子的同时让它沿光子方向自动走一格
+		p.x += p.mx;
+		p.y += p.my;
+		p.z += p.mz;
+		int rx = Math.round(p.x);
+		int ry = Math.round(p.y);
+		int rz = Math.round(p.z);
+		if (Frog.outBrainBound(rx, ry, rz))
+			return;// 出界直接扔掉
+		Cell cell = getCell(rx, ry, rz);
+		if (cell != null) {
+			cell.addPhoton(p);
+			cell.digHole(p);
+		}
+	}
+
+	// for test purpose, reset some values for prepare next training.
+	public void prepareNewTraining() {
+		for (int i = 0; i < Env.FROG_BRAIN_XSIZE; i++) {
+			if (cells[i] != null)
+				for (int j = 0; j < Env.FROG_BRAIN_YSIZE; j++)
+					if (cells[i][j] != null)
+						for (int k = 0; k < Env.FROG_BRAIN_ZSIZE; k++) {
+							Cell cell = cells[i][j][k];
+							if (cell != null) {
+								cell.deleteAllPhotons();
+								cell.hasInput = false;
+								cell.photonSum = 0;
+								if (cell.holes != null)
+									for (Hole h : cell.holes) {
+										h.age += 100;// 强迫洞的年龄增加,用这个方法来区分开不同批次的训练
+									}
+							}
+						}
+		}
+	}
+
+}