CMSC 433, Alan Sussman, U. Maryland
(via Bill Pugh) 1
CMSC433, Spring 2001
Programming Language
Technology and Paradigms
Basic Java, continued
Alan Sussman
October 4, 2001
CMCS 433, Fall 2001 -Alan Sussman 2
Administrivia
•Java project due Friday, 6PM
–see TA or Dr. Porter for questions
•Second Java project posted soon
•Practice midterm posted, with answers
–there are topics on there that we haven’t gotten
to yet
•but only topics covered in lecture will be on the
exam
CMCS 433, Fall 2001 -Alan Sussman 3
Last time -Java
•Constructors
–call another constructor or super() first
•Static methods/instance variables
–associated with Class object
•Types –primitive, class, array, interface
•Object obligations –equals(), toString(), clone(),
etc.
–write them if you don’t want the default implementation
•Use Object for polymorphism
–need to downcast to actual type before using a reference
declared as Object
Interacting with External
Environment
CMCS 433, Fall 2001 -Alan Sussman 5
Applications and I/O
•Java external interface is a public class
•via public static void main(String [] args)
•args[0] is first argument
–unlike C/C++
•System.out and System.err are PrintStreams’s
–should be PrintWriter’s, but would break 1.0 code
–System.out.print(…)prints a string
–System.out.println(…)prints a string with a newline
•System.in is an InputStream
–not quite so easy to use
CMCS 433, Fall 2001 -Alan Sussman 6
Input (JDK 1.1 and higher)
•Wrap System.in in an InputStreamReader
–converts from bytes to characters
•Wrap the result in a BufferedReader
–makes input operations efficient
–supports readline() interface
•readline() returns a string
–returns null if at EOF
