Transcript Move - Buncombe County Schools

• Classes begin with capital letters (i.e.
UrRobot). Methods, objects, and variable
names begin with lower case (camelCase)
• Use indentation to line up statements
• Brackets {} should be on a line by themselves
• Use comments // to identify what the code is
supposed to do (very useful)
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• A Definition of Symbol: A symbol is a written word or
sequence of characters used to represent something else.
• Special symbols: ; {} . (they mean something special in
Java)
• Names are symbols: karel, UrRobot, putBeeper. UrRobot is
not a robot itself, but represents a type of robot.
• Reserved words are symbols: class, void, new (they have a
built-in purpose)
Note: Symbols must match in case when used in Java programs
(i.e. karel is not the same as Karel and putBeeper is not the
same as PutBeeper)
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(Errors are referred to as bugs)
• lexical error (compiler catches)
– word not in its dictionary (i.e. you type MOVE() instead of move() )
• syntax error (compiler catches)
– incorrect grammar, punctuation, incorrect location of a statement (i.e.
leaving out a parenthesis or using a colon instead of semi-colon)
• execution error (run-time environment catches)
– can’t perform what you ask (i.e. error shutoff if performing move()
when a wall is in the way)
• intent error (logic - guess who catches this one!)
– program terminates successfully – junk output, however (i.e. moving
robot to the wrong corner)
Which is the hardest type of error to correct? Why?
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IDENTIFY THE BUGS
(Clue: There are at least 9 errors)
public Class SampleTest implements Directions
{
public static void main(String args[]
{
UrRobot karel = New UrRobot(2, 1, East, 0).
karel.move();
karel.turnLeft()
getBeeper();
karel.Move();
karel.turnOff;
karel.move();
}
}
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IDENTIFY THE BUGS
SOLUTION
public Class
class SampleTest implements Directions
1) should be class instead of Class
{
public static void main(String args[]
args[]) 2) needs parentheses
{
UrRobot karel = New
new UrRobot(2, 1, East, 0).
0);.
3) should be new instead of New
4) use semi-colon instead of period
karel.move();
karel.turnLeft()
karel.turnLeft();
5) needs a semi-colon on end
getBeeper();
karel.pickBeeper(); 6) needs an object and is named pickBeeper
karel.Move();
karel.move();
7) Move is not a method
karel.turnOff;
karel.turnOff();
8) needs () (i.e. turnOff() );
karel.move();
9) can’t perform move after turnOff
}
}
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Now You Try Writing a Short
Program to Draw the Letter H
•
•
•
•
•
•
Robot starts at origin (1,1), facing north
Robot draws the letter H
The bottom of the left bar of the H starts at (2,2)
The H is 5 beepers high
The middle bar should be 2 beepers between the bars
Robot should return to origin, face north, and turn
itself off when finished (leaving the world in its original
state of being
Take a little time to think about the best approach before jumping into
the code. It may help to sketch the robot’s path on a sheet of paper.
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DrawH program
Starting Point
import kareltherobot.*;
public class DrawH_YOURNAME implements Directions
{
public static void main(String args[])
{
World.setVisible(true);
UrRobot karel = new UrRobot(1, 1, North, infinity);
// …….insert your code here to draw the letter H
}
}
Name your class like this: (i.e. DrawH_JohnDoe)
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Beginning Situation
Ending Situation
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Copying Classes between
School and Home
• Since there are times when you will want to continue your work at
home, you will need to be able to transfer your code back and forth.
This is where your flash drive becomes handy.
• To reduce confusion, keep the folder structure on your flash drive the
same as the folder structure on your school computer
• Use file manager to locate the Java source file (that has extension
.java) within the package folder.
• Copy only the .java files (not the .class files) to your flash drive
folder.
• You can then copy these files to your package folder on your
destination computer.
• Note: After you launch jGRASP, it is important to refresh the
project.
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