Karel机器人：从基础教学到Java编程的历程

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Karel the Robot: A Pioneering Approach to Teaching Programming Fundamentals 在20世纪70年代，斯坦福大学的一名研究生Rich Pattis意识到，通过简化编程环境来教授编程基础将更为有效，使学生能够摆脱复杂语言结构的困扰。他借鉴了麻省理工学院Seymour Papert的LOGO项目的成功经验，设计了一种初级编程环境，让学生能够指导一个名为Karel的机器人解决简单问题。Karel的设计灵感源于捷克剧作家卡雷尔·恰佩克的1923年戏剧《罗素姆的通用机器人》（R.U.R.），这部作品首次将"机器人"一词引入英语。 Karel机器人教材是由Eric Roberts编写的，它成为计算机科学入门课程的重要工具，特别是在斯坦福大学的CS106A课程中。这个教材的成功在于其直观性，学生们通过操纵Karel在二维空间中移动、捡拾豆子等简单的任务，逐步理解编程逻辑和控制流程。教材销量超过10万册，见证了无数初学者通过实践与Karel互动，逐渐掌握编程基本概念。然而，随着时间的推移，Karel模拟器在20世纪90年代中期面临更新换代的需求。尽管Karel作为教学工具曾经非常流行，但它可能已经不能满足现代教育中对更先进技术和实践能力培养的需求。尽管如此，Karel的历史地位不容忽视，它代表了一种创新的教学方法，通过寓教于乐的方式帮助初学者建立起坚实的编程基础。 Karel的故事提醒我们，教育技术的发展和适应是持续的过程。随着新的编程语言和平台的出现，寻找并创造适合不同学习阶段和兴趣的教学工具仍然是教育者的重要职责。尽管Karel可能不再是当前主流的选择，但其理念和影响力对编程教育的长远发展产生了深远影响。对于那些希望回顾编程教育历史或者寻找传统教学方法的借鉴者来说，Karel the Robot学习Java的经历依然是一段值得深入研究的宝贵篇章。

Chapter 2

Programming Karel

In its new object-oriented implementation, the simplest style of Karel program consists of

a definition of a new Karel class that specifies a sequence of built-in commands that

should be executed when the program is run. A very simple Karel program is shown in

Figure 1.

Figure 1. Simple Karel example to pick up a single beeper

* File: BeeperPickingKarel.java

* -----------------------------

* The BeeperPickingKarel class extends the basic Karel class

* by defining a "run" method with three commands. These

* commands cause Karel to move forward one block, pick up

* a beeper, and then move ahead to the next corner.

import stanford.karel.*;

public class BeeperPickingKarel extends Karel {

public void run() {

move();

pickBeeper();

move();

}

The program in Figure 1 is composed of several parts. The first part consists of the

following lines:

* File: BeeperPickingKarel.java

* -----------------------------

* The BeeperPickingKarel class extends the basic Karel class

* by defining a "run" method with three commands. These

* commands cause Karel to move forward one block, pick up

* a beeper, and then move ahead to the next corner.

These lines are an example of a comment, which is simply text designed to explain the

operation of the program to human readers. Comments in both Karel and Java begin with

the characters /* and end with the characters */. Here, the comment begins on the first

line and ends several lines later. The stars on the individual lines that make up the text of

the comment are not required, but make it easier for human readers to see the extent of

the comment. In a simple program, extensive comments may seem silly because the

effect of the program is obvious, but they are extremely important as a means of

documenting the design of larger, more complex programs.

The second part of the program is the line

import stanford.karel.*;

This line requests the inclusion of all definitions from the stanford.karel library. This

library contains the basic definitions necessary for writing Karel programs, such as the

definitions of the standard operations move() and pickBeeper(). Because you always

need access to these operations, every Karel program you write will include this import

command before you write the actual program.

The final part of the Karel program consists of the following class definition:

public class BeeperPickingKarel extends Karel {

public void run() {

move();

pickBeeper();

move();

}

To understand this definition, it is useful to look more carefully at its structure. The

definition of the BeeperPickingKarel class consists of the line beginning with

public class and encompasses everything between the curly brace at the end of that line

and the corresponding closing brace on the last line of the program. The single line that

introduces the new class is called the header of the definition; the code between the

braces is called the body.

In programming, it is often very useful to think about a particular definition and its

body as separable ideas. In this example, the definition of

BeeperPickingKarel has the

following form, where the entire body of the definition has been replaced by a box that

you can put out of your mind for the moment:

public class BeeperPickingKarel extends Karel {

body of the class definition

}

The header line at the top tells you quite a bit about the BeeperPickingKarel class, even

before you have looked to see what the body contains. The key new concept in the class

header is embodied in the word extends, which is used in both Karel and Java to indicate

that a new class is an extension of an existing one. Here, the class header line indicates

that BeeperPickingKarel is an extension of the standard Karel class imported from the

stanford.karel library.

In object-oriented languages, defining a new class by extension means that the new

class (here,

BeeperPickingKarel) builds on the facilities provided by the existing class

(in this case, Karel). In particular, the fact that it extends Karel guarantees that the new

BeeperPickingKarel class will have the following properties :

1. Any instance of the class

BeeperPickingKarel is also an instance of the class Karel.

Any instance of the class Karel represents a robot that lives in a world of streets,

avenues, beepers, and walls whose state consists of its location, direction, and the

number of beepers in its bag. Because BeeperPickingKarel is an extension of

Karel, you know that an instance of BeeperPickingKarel will also be a robot that

lives in the same type of world and has the same state properties.

2. Any instance of the

BeeperPickingKarel class will automatically respond to the

same commands as an instance of the Karel class. Because every robot in the Karel

class knows how to respond to the commands move(), turnLeft(), pickBeeper(),

and putBeeper(), it follows that a instance of BeeperPickingKarel will understand

that same set of commands.

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