- In this lab, students must write
2 Java programs to evaluate an
arithmetic expression
- One program must use if-else-statements
- The other program must use a switch-statement
- The lab assignment is self-explanatory and your job is to assist students (show them the answers) when they have questions.
- In this lab you will:
- Learn about command line arguments
- Convert command line arguments to
integer
- Use if-else-statement and the switch-statement to write programs to evaluate a simple expression.
Please, make sure that you have added the honor code statement at the top of your Java file:
/* THIS CODE IS MY OWN WORK, IT WAS WRITTEN WITHOUT CONSULTING CODE WRITTEN BY OTHER STUDENTS. _Your_Name_Here_ */
The deadline for completing this lab assignment is midnight, today.
- Learn about command line arguments
- Copy-and-paste these terminal commands:
mkdir ~/cs170/lab4 cp ~cs170002/share/lab4/* ~/cs170/lab4 cd ~/cs170/lab4
In this lab, we will use gedit and javac (not BlueJ !)
- When you run a Java program using
additional parameters, the
additional parameters are called
command line arguments
- Example:
java myProgram x y zThe additional parameters x, y and z are command line arguments.
- The values of the
command line arguments are
passed (i.e., given) to a Java program
through the
parameter in the
main()
method.
Example:
public static void main( String[] args ) { .... }Explanation:
- The parameter of the
main() method
is the variable args.
- This variable
args stores (contains) the
values command line arguments as
follows:
args[0] contains the value of the first command line argument args[1] contains the value of the second command line argument args[2] contains the value of the third command line argument and so on...
(Remember that computer starts counting at ZERO (0), humans usually start counting at ONE (1)....)
- The parameter of the
main() method
is the variable args.
- The type of
the variables
arg[0],
arg[1], and so on,
are String
- So if you specify a number
as a command line argument, the
main() will store it as
the type String
- So if you want to do calculation with that number,
you need to convert it
to an int or
double first.
- Recall that:
Integer.parseInt( " .... " ) converts a String to an int value Double.parseDouble( " .... " ) converts a String to a double value
- The programs Arithmetic1.java
and
Arithmetic2.java
takes
three command-line arguments:
- two integers,
- followed by an arithmetic operator (+, -, * or /).
- Both programs
(Arithmetic1.java
and
Arithmetic2.java)
prints the result of the
arithmetic expression
- Sample correct result:
(don't type the text after the #
sign)
UNIX>> javac Arithmetic1.java # Compile UNIX>> java Arithmetic1 1 2 + # Execute 1+2=3 UNIX>> java Arithmetic1 3 2 * # Execute 3*2=6 UNIX>> java Arithmetic1 3 2 ? # Execute Error: invalid operator!
The program Arithmetic2.java will produce the same results.
- Open Arithmetic1.java
for editing
- Enter the following commands in
a Terminal window:
cd ~/cs170/lab4 gedit Arithmetic1.java &You will see the following window:
- Enter the following commands in
a Terminal window:
- How to
compile and
run
Arithmetic1.java
- After you made the changes to
Arithmetic1.java,
you must save the file
by clicking on the
save button:
- You must first compile
Arithmetic1.java with
this command in a Terminal window:
javac Arithmetic1.java
(Make sure your current directory is /home/YOURID/cs170/lab4.)
- After you have successfully compiled
Arithmetic1.java, you can run
it with the following command:
java Arithmetic1 number1 number2 operator Example: java Arithmetic1 1 2 +
- After you made the changes to
Arithmetic1.java,
you must save the file
by clicking on the
save button:
- Complete Arithmetic1.java by:
- Adding a statement to
obtain the second operand into
the variable operand2
The location of this statement is here:
For hints on what to do, look at how the program obtains the first operand into the variable operand1 (shown in the figure above)
- Complete the nested if-else-statement
that perform the selected operation and
prints the result.
The location of this statement is here:
For hints on what to do, look at the first part of the code where the '-' operation is handled (shown in the figure above).
Add cases to handle: '+', * and /.
In the last else, you should handle the case when the operation is not any of '+', '-', '*' or '/' by printing the message:
"Error: invalid operator!"
When you're done, please exit gedit by clicking on the CLOSE button (located at top-right of the gedit window)
- Adding a statement to
obtain the second operand into
the variable operand2
- Open Arithmetic2.java
for editing
- Enter the following commands in
a Terminal window:
cd ~/cs170/lab4 gedit Arithmetic2.java &You will see the following window:
- Enter the following commands in
a Terminal window:
- How to
compile and
run
Arithmetic2.java
- After you made the changes to
Arithmetic2.java,
you must save the file
by clicking on the
save button.
- You must first compile
Arithmetic2.java with
this command in a Terminal window:
javac Arithmetic2.java
(Make sure your current directory is /home/YOURID/cs170/lab4.)
- After you have successfully compiled
Arithmetic2.java, you can run
it with the following command:
java Arithmetic2 number1 number2 operator Example: java Arithmetic2 1 2 +
- After you made the changes to
Arithmetic2.java,
you must save the file
by clicking on the
save button.
- Complete Arithmetic2.java by:
- Adding a statement to
obtain the second operand into
the variable operand2
The location of this statement is here:
- Complete the switch-statement
that perform the selected operation and
prints the result.
The location of this statement is here:
For hints on what to do, look at the first part of the code where the '-' operation is handled (shown in the figure above).
Add cases to handle: '+', * and /.
In the default case, you should handle the case when the operation is not any of '+', '-', '*' or '/' by printing the message:
"Error: invalid operator!"
- Adding a statement to
obtain the second operand into
the variable operand2
- You must turn in your work
by enter these terminal commands:
cd ~/cs170/lab4 /home/cs170002/turnin-lab Arithmetic1.java lab4 /home/cs170002/turnin-lab Arithmetic2.java lab4a
For the Lead TA:
- Make sure that when a student leaves the lab that he/she has turned in his/her work !!!