Programming Language Technologies and Paradigm - Basic Java | CMSC 433, Study notes of Programming Languages

Download Programming Language Technologies and Paradigm - Basic Java | CMSC 433 and more Study notes Programming Languages in PDF only on Docsity! CMSC 433,Michael Hicks, U. Maryland (via W. Pugh, A. Sussman, and A, Porter) 1 CMSC433, Fall 2002 Programming Language Technology and Paradigms Basic Java Michael Hicks Sep 12, 2002 CMCS 433, Fall 2002 - Michael Hicks 59 Exceptions • On an error condition, we throw an exception • At some point up the call chain, the exception is caught and the error is handled • Separates normal from error-handling code • A form of non-local control-flow – Like goto, but structured CMSC 433,Michael Hicks, U. Maryland (via W. Pugh, A. Sussman, and A, Porter) 2 CMCS 433, Fall 2002 - Michael Hicks 60 Throwing an Exception • Create a new object of the class Exception, and throw it if (i > 0 && i < a.length ) { return (a[I]) } else throw new ArrayIndexOutOfBounds(); • Exceptions thrown are part of return type – when overriding a method in a superclass – can’t throw anything that would surprise a superclass object CMCS 433, Fall 2002 - Michael Hicks 61 Method throws declarations • A method declares the exceptions it might throw – public void openNext() throws UnknownHostException, EmptyStackException { … } • Must declare any exception the method might throw – unless it is caught in the method – includes exceptions thrown by called methods – certain built-in exceptions excluded CMSC 433,Michael Hicks, U. Maryland (via W. Pugh, A. Sussman, and A, Porter) 5 Java Libraries CMCS 433, Fall 2002 - Michael Hicks 67 You should familiarize yourself • Packages – java.lang – java.util – java.net – java.io • Read the documentation on line CMSC 433,Michael Hicks, U. Maryland (via W. Pugh, A. Sussman, and A, Porter) 6 I/O and Network Libraries CMCS 433, Fall 2002 - Michael Hicks 69 • Raw communication takes place using streams • Java also provides readers and writers • Applies to files, network connections, strings, etc. I/O streams InStream OutStream Process CMSC 433,Michael Hicks, U. Maryland (via W. Pugh, A. Sussman, and A, Porter) 7 CMCS 433, Fall 2002 - Michael Hicks 70 I/O Classes • OutputStream – byte stream going out • Writer – character stream going out • InputStream – byte stream coming in • Reader – character stream coming in CMCS 433, Fall 2002 - Michael Hicks 71 OutputStream - bytes • Example classes – ByteArrayOutputStream – goes to byte [] – FileOutputStream – goes to file • Wrappers – wrapped around OutputStream – BufferedOutputStream – ObjectOutputStream – serialization of object graph CMSC 433,Michael Hicks, U. Maryland (via W. Pugh, A. Sussman, and A, Porter) 10 CMCS 433, Fall 2002 - Michael Hicks 76 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 CMCS 433, Fall 2002 - Michael Hicks 77 Example Echo Application import java.io.*; public class Echo { public static void main(String [] args) { String s; BufferedReader in = new BufferedReader( new InputStreamReader(System.in)); int i = 1; try { while((s = in.readLine()) != null) System.out.println((i++) + “: “ + s); } catch(IOException e) { System.out.println(e); } } } CMSC 433,Michael Hicks, U. Maryland (via W. Pugh, A. Sussman, and A, Porter) 11 CMCS 433, Fall 2002 - Michael Hicks 78 Java Networking • class Socket – Client-side connections to servers • class ServerSocket – Server-side “listen” socket – Awaits and responds to connection requests CMCS 433, Fall 2002 - Michael Hicks 79 Example Client/Server ServerSocket s = new ServerSocket(5001); Socket conn = s.accept(); InputStream in = conn.getInputStream(); OutputStream out = conn.getOutputStream(); Socket conn = new Socket (5001); InputStream in = conn.getInputStream(); OutputStream out = conn.getOutputStream(); Client code Server code server client CMSC 433,Michael Hicks, U. Maryland (via W. Pugh, A. Sussman, and A, Porter) 12 CMCS 433, Fall 2002 - Michael Hicks 80 Example Client/Server ServerSocket s = new ServerSocket(5001); Socket conn = s.accept(); InputStream in = conn.getInputStream(); OutputStream out = conn.getOutputStream(); Socket conn = new Socket (5001); InputStream in = conn.getInputStream(); OutputStream out = conn.getOutputStream(); Client code Server code server client CMCS 433, Fall 2002 - Michael Hicks 81 Example Client/Server ServerSocket s = new ServerSocket(5001); Socket conn = s.accept(); InputStream in = conn.getInputStream(); OutputStream out = conn.getOutputStream(); Socket conn = new Socket (5001); InputStream in = conn.getInputStream(); OutputStream out = conn.getOutputStream(); Client code Server code server client ? CMSC 433,Michael Hicks, U. Maryland (via W. Pugh, A. Sussman, and A, Porter) 15 Utility Libraries CMCS 433, Fall 2002 - Michael Hicks 87 java.util • Lots of stuff – Vector – Dictionaries – Enumerations and Bitsets – Container classes • We will focus on Container classes CMSC 433,Michael Hicks, U. Maryland (via W. Pugh, A. Sussman, and A, Porter) 16 CMCS 433, Fall 2002 - Michael Hicks 88 Other libraries • java.lang.Math – abstract final class – only static members – includes constants e and π – includes static methods for trig, exponentiation, min, max, … • java.text – text formatting tools • class MessageFormat provides printf/scanf functionality – lots of facilities for internationalization CMCS 433, Fall 2002 - Michael Hicks 89 Java Container Classes • A unified architecture for representing and manipulating collections of objects • Container classes contain three things: – Interfaces: abstract data types representing collections of objects – Implementations: concrete implementations of the collection interfaces – Algorithms: methods that perform computations on objects that implement collection interfaces CMSC 433,Michael Hicks, U. Maryland (via W. Pugh, A. Sussman, and A, Porter) 17 CMCS 433, Fall 2002 - Michael Hicks 90 Container class hierarchy CMCS 433, Fall 2002 - Michael Hicks 91 Collection Classes • Collections contain groups of objects (elements) • Collection interface is not implemented in Java. Subinterfaces implemented – Set: unordered, can’t contain duplicate elements • Hashset – unordered, no duplicates • TreeSet - ordered, no duplicates – List: ordered, can contain duplicate elements • LinkedList – unordered, dynamic size, add/delete quick • ArrayList – unordered, dynamic size, random access CMSC 433,Michael Hicks, U. Maryland (via W. Pugh, A. Sussman, and A, Porter) 20 CMCS 433, Fall 2002 - Michael Hicks 96 Example1 import java.util.*; import java.awt.*; class MyPoint extends java.awt.Point implements Comparable { MyPoint(int x, int y) {super(x,y);} public int compareTo(Object o) { MyPoint p = (MyPoint)o; double d1 = Math.sqrt(x*x + y*y); double d2 = Math.sqrt(p.x*p.x + p.y*p.y); if (d1 < d2) {return -1;} else if (d2 < d1) {return 1;} return 0; } } class Sort3 { public static void main(String[] args) { Random rnd = new Random(); MyPoint[] points = new MyPoint[10]; for (int i=0; i<points.length; i++) { points[i] = new MyPoint (rnd.nextInt(100),rnd.nextInt(100)); System.out.println(points[i]); } System.out.println("-----------"); Arrays.sort(points); //Print the points for (int i=0; i<points.length; i++){ System.out.println(points[i]); } } } CMCS 433, Fall 2002 - Michael Hicks 97 Example2 import java.util.*; import java.awt.*; class MyPoint extends java.awt.Point implements Comparable { MyPoint(int x, int y) { super(x, y); } public int compareTo(Object o) { MyPoint p = (MyPoint)o; return x - p.x; } } class Sort2 { public static void main(String[] args) { Random rnd = new Random(); MyPoint[] points = new MyPoint[10]; for (int i=0; i<points.length; i++) { points[i] = new MyPoint (rnd.nextInt(100), rnd.nextInt(100)); System.out.println(points[i]); } System.out.println("-----------"); Arrays.sort(points); //Print the points for (int i=0; i<points.length; i++){ System.out.println(points[i]); } } } CMSC 433,Michael Hicks, U. Maryland (via W. Pugh, A. Sussman, and A, Porter) 21 CMCS 433, Fall 2002 - Michael Hicks 98 Output Sort2 …….. // after sort MyPoint[x=1,y=95] MyPoint[x=2,y=16] MyPoint[x=3,y=26] MyPoint[x=12,y=95] MyPoint[x=22,y=55] MyPoint[x=30,y=73] MyPoint[x=31,y=42] MyPoint[x=66,y=33] MyPoint[x=70,y=33] MyPoint[x=80,y=31] Sort3…….. // after sort MyPoint[x=2,y=0] MyPoint[x=0,y=15] MyPoint[x=18,y=4] MyPoint[x=39,y=13] MyPoint[x=39,y=19] MyPoint[x=42,y=23] MyPoint[x=65,y=5] MyPoint[x=38,y=74] MyPoint[x=80,y=40] MyPoint[x=87,y=62] This document was created with Win2PDF available at http://www.daneprairie.com. The unregistered version of Win2PDF is for evaluation or non-commercial use only.