😕 Brauchst du Hilfe beim Installieren in Windows?
📺 Dann schau dir Karel The Robot installieren in Windows an!
Karel The Robot is a simple teaching environment for imperative programming basics. The original idea was developed in the 1970s by Richard Pattis at Stanford University:
In the 1970s, a Stanford graduate student named Rich Pattis decided that it would be easier to teach the fundamentals of programming if students could somehow learn the basic ideas in a simple environment free from the complexities that characterize most programming languages.
In sophisticated languages like Java, there are so many details that learning these details often becomes the focus of the course. When that happens, the much more critical issues of problem solving tend to get lost in the shuffle. By starting with Karel, you can concentrate on solving problems from the very beginning. And because Karel encourages imagination and creativity, you can have quite a lot of fun along the way.
This project started in 2012 due to dissatisfaction with the available Karel environments. Since then, thousands of German university students have been introduced to the basics of imperative programming via this project.
😕 Brauchst du Hilfe beim Installieren in Windows?
📺 Dann schau dir Karel The Robot installieren in Windows an!
Please take the time to read the following instructions carefully. Most problems stem from skipping or misunderstanding important steps.
-
Visit https://adoptium.net
-
Click "Latest release" button to download Java installer
-
Wait for download to finish
-
Open the
Downloads
folder (via Windows Explorer or Finder/Spotlight, respectively) and double-clickOpenJDK...
to start Java installer -
Click Next, Next, Install, Finish
-
Click karel.jar to download Karel
If Karel fails to download, continue with⚠️ Troubleshooting Windows, or⚠️ Troubleshooting macOS -
Open the
Downloads
folder and double-clickkarel.jar
to start Karel
If Karel fails to start, continue with⚠️ Troubleshooting Windows, or⚠️ Troubleshooting macOS
Steps 1 through 5 (install Java) worked, but steps 6 (download Karel) or 7 (start Karel) failed? Then read on.
- Move your mouse over the script below
- A button appears in the top right corner of the script
- Click that button to copy the script
cd Downloads
if exist karel.jar.zip erase karel.jar.zip
curl -o karel.jar https://raw.githubusercontent.com/fredoverflow/karel/release/karel.jar
echo java -version > karel.cmd
echo java -jar karel.jar >> karel.cmd
karel.cmd
- Press the Windows key (the key on the bottom left with the Windows logo ⊞ on it)
- Write
cmd
and confirm with Enter - A terminal appears
- Right-click anywhere inside that terminal to paste and execute the script
From now on, simply double-click karel.cmd
in the Downloads
folder to start Karel.
Feel free to move karel.jar
and karel.cmd
to the Desktop or any other folder you prefer.
Steps 1 through 5 (install Java) worked, but steps 6 (download Karel) or 7 (start Karel) failed? Then read on.
- Move your mouse over the script below
- A button appears in the top right corner of the script
- Click that button to copy the script
cd Downloads
curl -o karel.jar https://raw.githubusercontent.com/fredoverflow/karel/release/karel.jar
chmod +x karel.jar
echo java -version > karel.sh
echo java -jar karel.jar >> karel.sh
chmod +x karel.sh
./karel.sh
- Press
Command⌘ Space
(or click the magnifying glass 🔍 in the top right corner of the screen) to open Spotlight - Write
terminal
and confirm with Enter - A terminal appears
- Press
Command⌘ V
to paste and execute the script
From now on, simply double-click karel.sh
in the Downloads
folder to start Karel.
Feel free to move karel.jar
and karel.sh
to the Desktop or any other folder you prefer.
sudo apt install default-jdk
cd Downloads
curl -o karel.jar https://raw.githubusercontent.com/fredoverflow/karel/release/karel.jar
chmod +x karel.jar
echo java -version > karel.sh
echo java -jar -Dsun.java2d.opengl=True karel.jar >> karel.sh
chmod +x karel.sh
./karel.sh
From now on, simply double-click karel.sh
in the Downloads
folder to start Karel.
Feel free to move karel.jar
and karel.sh
to the Desktop or any other folder you prefer.
Your code is automatically saved to a new file each time you click the start button.
The save folder is named karel
, and it is located in your home directory.
The full path is displayed in the title bar.
Shortcut | Command | Meaning |
---|---|---|
F1 | moveForward(); |
Karel moves one square forward in the direction he currently faces. Fails if a wall blocks the way. |
F2 | turnLeft(); |
Karel turns 90° to the left. |
F3 | turnAround(); |
Karel turns 180° around. |
F4 | turnRight(); |
Karel turns 90° to the right. |
F5 | pickBeeper(); |
Karel picks a beeper from the square he currently stands on. Fails if there is no beeper. |
F6 | dropBeeper(); |
Karel drops a beeper onto the square he currently stands on. Fails if there already is a beeper. |
Sometimes the same sequence of commands appears multiple times:
void roundTrip()
{
moveForward();
moveForward();
moveForward();
moveForward();
moveForward();
moveForward();
moveForward();
moveForward();
moveForward();
turnAround();
moveForward();
moveForward();
moveForward();
moveForward();
moveForward();
moveForward();
moveForward();
moveForward();
moveForward();
}
You can extract such a sequence of commands into a new, custom command:
void moveAcrossWorld()
{
moveForward();
moveForward();
moveForward();
moveForward();
moveForward();
moveForward();
moveForward();
moveForward();
moveForward();
}
and use it just like a primitive command:
void roundTrip()
{
moveAcrossWorld();
turnAround();
moveAcrossWorld();
}
Deciding when a sequence of commands is worth extracting and choosing a good name for the custom command are essential development skills you will acquire over time.
Instead of writing the same sequence of commands multiple times:
void dance()
{
moveForward();
turnLeft();
moveForward();
turnLeft();
moveForward();
turnLeft();
moveForward();
turnLeft();
}
you can use repeat
and only write it once:
void dance()
{
repeat (4)
{
moveForward();
turnLeft();
}
}
Sometimes you only want to do something if some condition holds:
if (onBeeper())
{
pickBeeper();
}
Optionally, you can also specify what to do in case the condition does not hold:
if (onBeeper())
{
pickBeeper();
}
else
{
dropBeeper();
}
Note that conditions are only checked when control flow actually reaches them (when the corresponding line is highlighted in the code editor). Conditions are not periodically checked in the background! In large programs with lots of potentially contradicting conditionals, such periodic background checks would quickly lead to incomprehensible program behavior.
Shortcut | Condition | Meaning |
---|---|---|
F7 | onBeeper() |
Karel checks whether a beeper is on the square he currently stands on. |
F8 | beeperAhead() |
Karel checks whether a beeper is on the square immediately in front of him. |
F9 | leftIsClear() |
Karel checks whether no wall is between him and the square to his left. |
F10 | frontIsClear() |
Karel checks whether no wall is between him and the square in front of him. |
F11 | rightIsClear() |
Karel checks whether no wall is between him and the square to his right. |
An else
with nothing but another if
inside:
if (leftIsClear())
{
turnLeft();
}
else
{
if (rightIsClear())
{
turnRight();
}
}
can be simplified by leaving out the block between the else
and if
:
if (leftIsClear())
{
turnLeft();
}
else if (rightIsClear())
{
turnRight();
}
Note that without the else
, Karel might turn left and then immedately turn right again, given frontIsClear()
originally held.
The else
prevents the second if
from executing in case the first condition was already true
.
An if/else
with an empty first block:
if (onBeeper())
{
}
else
{
dropBeeper();
}
can be simplified by negating the condition with a leading !
:
if (!onBeeper())
{
dropBeeper();
}
An if
with nothing but another if
inside:
if (frontIsClear())
{
if (beeperAhead())
{
moveForward();
pickBeeper();
}
}
can be simplified by combining both conditions with &&
:
if (frontIsClear() && beeperAhead())
{
moveForward();
pickBeeper();
}
An if/else if
with identical blocks:
if (!frontIsClear())
{
turnRight();
}
else if (beeperAhead())
{
turnRight();
}
can be simplified by combining both conditions with ||
:
if (!frontIsClear() || beeperAhead())
{
turnRight();
}
Condition | Meaning |
---|---|
!a |
holds if a does not hold (and vice versa) |
a && b |
holds if both a and b hold |
a || b |
holds if a or b (or both) hold |
a || !b && c |
a || ((!b) && c) |
if
checks the condition and then executes the block at most once:
void moveForwardSafely()
{
if (frontIsClear())
{
moveForward(); // This line is executed 0 or 1 times
}
}
while
re-checks the condition after the block is executed:
void moveToWall()
{
while (frontIsClear())
{
moveForward(); // This line is executed 0 to 9 times
}
}
Windows | Effect | Macintosh |
---|---|---|
F1 | moveForward(); |
F1 |
F2 | turnLeft(); |
F2 |
F3 | turnAround(); |
F3 |
F4 | turnRight(); |
F4 |
F5 | pickBeeper(); |
F5 |
F6 | dropBeeper(); |
F6 |
F7 | onBeeper() |
F7 |
F8 | beeperAhead() |
F8 |
F9 | leftIsClear() |
F9 |
F10 | frontIsClear() |
F10 |
F11 | rightIsClear() |
F11 |
F12 | start step into reset |
F12 |
Tab Enter |
auto-indent | Tab Enter |
Ctrl Space | auto-complete | Control (Shift) Space |
Ctrl Alt R | rename command | Command Option R |
Ctrl D | delete line | Command D |
Ctrl C | copy | Command C |
Ctrl X | cut | Command X |
Ctrl V | paste | Command V |
Ctrl Z | undo | Command Z |
Ctrl Y | redo | Command Y |