CMSC 433, Alan Sussman, U. Maryland (via
Bill Pugh) 1
CMSC433, Spring 2002
Programming Language
Technology and Paradigms
Basic Java, continued
Alan Sussman
February 5, 2002
CMCS 433, Spring 2002 -Alan Sussman 2
Administrivia
•Quiz returned today
•Revised version of project posted
–clarify myCounter behavior
–specify wire/socket format for timestamps
–sample code for creating a scrolling text
window
•Account issues?
–change those passwords!
CMCS 433, Spring 2002 -Alan Sussman 3
Last time
•Java basics
–statements, expressions, operators
–values –primitive types and references to
objects
–object operations –assignment, equals(),
toString(), clone(), getClass(), instanceof, cast
–arrays
CMCS 433, Spring 2002 -Alan Sussman 4
Array declarations
•int[] A and int A[] have identical semantics
–declares Ato be a variable containing a reference to an
array of ints
•int[] A[], B;
–A is a ref to an array of refs to arrays of ints
–Bis a ref to an array of ints
•None of these allocate an array
•A = new int [10]; allocates an array of 10 ints,
and makes Abe a reference to it
CMCS 433, Spring 2002 -Alan Sussman 5
Array example
int[] array1 = {1, 3, 5};
int[][] a = new int[10][3];
// a.length == 10
// a[7].length == 3
a[5][2] = 42;
a[9] = array1;
// a[9][2] == 5
// use of array initializers
int[][] twoD = {{1, 2, 3}, {4, 5}, {6}};
Object [] args = {“one”, “two”, a};
main(new String [] {“a”, “b”, “c”});
CMCS 433, Spring 2002 -Alan Sussman 6
String
•A class for representing non-mutable strings
•string constants converted to String
•+does string concatenation
•In some contexts objects automatically
converted to String type
•Example:
public static void printArray(Object [] a) {
for (int i = 0; i < a.length; i++)
System.out.println(“a[“ + i + “] = “ + a[i]);
}
