Wrap-up:
Where do we go from here?
CMPU-101: Problem-Solving and
Abstraction
Jennifer Walter
Vassar College
Spring 2008
Running and compiling code at the command line (i.e. the
"system prompt"):
1. Need to write main method in a public class:
public static void main (String[] args)
args is an array of Strings that is space-delimited and
whose elements are typed on the same line as the
command to execute the file.
2. To compile code at command line:
javac -classpath .:acm.jar
filename
.java
where filename is the file with the .java extension to
be compiled.
3. To run code at command line:
java -classpath .:acm.jar
filename
leave off the .java extension when running code.
The -classpath specifies location of acm.jar file.
4. To include arguments to the main method on the
command line when running code:
java -classpath .:acm.jar
filename 20 hi there
Note:
No extension used when running a program.
In this case, args.length = 3 and args[0] = "20", args[1]
= "hi", and args[2] = "there"
Printing to terminal without using acm.jar commands
•Use System.out.println("String to print");
System.out.print("String to print");
These methods are the same as the print and
println in acm.jar except they print to terminal
window.
•
System
is a class defined in the
java.lang
package.
This package is always imported by default and
includes commonly used classes like:
String,
Character, Math, Integer, Double, Boolean
•To read from the keyboard without using acm.jar,
you must declare a new Scanner and import
java.util.*, as was done in Assignment 10.
Static methods
•We did not cover the definition and use of static
methods in this class. A method is
static
if it
includes the keyword "static" in its signature.
•The main method is an example of a static method.
Other static methods we used were in the Math
class, the Character class, the RandomGenerator
class, and the System class. These methods are
called using the class name as a receiver rather
than using an object as the receiver.
•One limitation of static methods is that they cannot
call any non-static methods in their own class
directly. An object must be created on which to
call non-static methods.
Dealing with Exceptions in Java
1. Lines that generate exceptions when doing file input:
a. Instantiating a new Scanner for an input file.
b. Instantiating a new FileWriter for file output.
2. To deal with Exceptions:
a. Include a "throws Exception" clause on method
signature
b. Include a try{ } block around line that may cause
exception and follow it with a catch(Exception e){ }
to take appropriate action if an Exception occurs.
