CIS525 - Lecture#11 - October 11, 2000
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CIS 525 LECTURE 11 10/11/00
Java, continued
CHAPTER 8
2 basic data types - primitives, (built in), and reference, (pointer based)
Primitives: page 299
a) boolean
flag1 = false;
flag2 = (6 < 7);
flag3 = !true;
b) char
16 bit unsigned int
char c0 = 3;
char c1 = 'Q';
char c2 = '\u0000'; //smallest
char c3 = '\uffff'; //largest
char c4 = '\b'; //back space
char c5 = '\n'; //new line
char c6 = '\"'; //double quote
c) byte
8 bit 2's compliment
d) short
16 bit 2's compliment
e) int
32 bit 2's compliment
int i0 = 0;
int i1 = -12345;
int i2 = OxCafeBabe; //'magic numbers' for .class files
f) long
64 bit 2's compliment
g) float
32 bit IEEE 754
-1.23f
6.02E23f //exponential - can use either upper or lower case
h) double
64 bit IEEE 754
all else is 'reference'
Typecasts - explicit
converting among various types:
type2 type2Var = (type2)type1Var;
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Arithmetic Operators:
operators meaning
+,- addition, subtraction
*, /, % multiplication, division, modulo
++, -- prefix/postfix increment/decrement
<<, >>, >>> signed and unsigned shift
~ bitwise compliment
&, |, ^ bitwise and, or, not
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Conditional Operators:
a) if(expression)
statement1;
else
statement2;
b) expression ? val1 : val2; //val1 if true, val2 if false
c) switch(someInt) {
case val1: statement1;
break;
case val2: statement2;
break;
|
|
|
default:
statement;
}
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Boolean operators:
operators meaning
==, != equal, not equal, same as C++
<, <=, >, >= less than, less or equal, greater than, greater or equal
&&, || logical and, logical or
! logical negation
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Loops, page 312:
a) pre-test: // may not execute at all
i = 0;
while(i < bound) {
statement;
i++;
}
b) post-test: // will execute at least once
i = 0;
do {
statement;
}while( i < bound);
c) for loop:
for(i = 0; i < bound; i++) {
statement;
i++
}
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See pages 313-318 for a litany of math operations
Input and Output, page 319
a) print - standard out, (like 'cout' in C++)
(class PrintStream)
system.out.println(arg); //prints a new line each time
primitive types to strings:
string.valueOf();
non-string objects to strings
toString(); // method
system.out.flush(); // prints all data left in buffer
system.err)(); // prints standard error message
b) standard input, (like 'cin' in C++)
DataInputStream in = new DataInputSteam(system.in);
string urlString = in.ReadLine();
char urlChar = in.read Char();
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Stand Alone Java application, pg 320
=> CAN execute other programs
1) get a runtime object
Runtime rt = Runtime.getRuntime();
2) execute program
Process proc = rt.exec("someProgram");
3) OPTIONAL: wait for program to execute
proc.waitFor();
4) OPTIONAL: print the results, see page 321
BufferedInputStream = new BufferedInputStream(proc.getInputStream());
DataInputStream commandResult = new DataInputStream(buffer);
string S = null;
try{
while((s=commandResult.readLine())!=nul)
system.out.println("output: " + s);
commandResult.close();
}catch (Exception e)
{/* ignore read errors*/}
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Reference types, page 328
import java.awt.point
1) Point p1 = new Point(1,2); // (1,2) is x,y coordinates, p1.x, p1.y
2) Point p2 = p1; // this may result in aliasing problems, see below
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public static Point triple(Point p) {
p = new Point(p.x * 3, p.y * 3);
return p; //this would create memory leak in C++
}
triple(p2); // in Java, no explicit 'delete' is needed here
// as 'garbage collection' is used
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Arrays, page 346:
Like vectors, except vectors can grow in size - arrays cannot
int[] values = new int[2];
Point[] points = new Point[5]; // an array with 5 elements
values[0] = 10;
values[1] = 100;
for(int i = 0; i < point.length; i++) {
points[i] = new point(i * 2, i * 4); // new values for
// x & y coordinates
}
Multi-dimensional arrays, page 348:
int[][] values = new int[12][14]; // init a 12 x 14 array
for(int i = 0; i < 12; i++) {
for(int j = 0; j < 14; j++) {
values[i][j] = 0;
}
}
String[][] name0={"John", "Q", "Public"};
name1={"Jane", "Doe"};
name2={"Pele"};
since Java is an interpretted language, this is allowable, not all
array entries need to have the same dimensions
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