Lecture 4 JA V A (46-935) Somesh Jha 1 Inner Classes Flash - PDF document

Lecture 4 JA V A (46-935) Somesh Jha 1

Inner Classes Flash bac k to the class. A bstr actT ermStructur e � There w as a whic h SlowYieldV olObje ct � computed: ( i = 0) Di�erence b et w een and c ompute d yield { the market yield (otherwise) Di�erence b et w een c ompute d { and the volatility . volatility market The ob ject used b y the Clumsy! NewtonR aphson � solv er b elongs in the class. T ermStructur e Nob o dy else uses it. � 2

Inner Classes (Con td) Put a class inside the YieldV olObje ct � class. T ermStructur e Nob o dy else except class can use T ermStructur e � the ct . YieldV olObje These are called classes . memb er � There are other kind of inner classes. (Read � Chapter 5). 3

Co de F ragmen t /** Abstract class for building a BDT type interest-rate model. @author Somesh Jha */ package interestRate; import mathUtil.*; public abstract class TermStructure { private static final boolean DEBUG=false; //time horizon int T; //Used by the Newton-Raphson solver YieldVolObject slowYieldVolObj; NewtonRaphson slowSolver; //parameters of the BDT model double r[]; double k[]; //bond yields and yield volatilities //at time 0 double yield[]; double volatilities[]; //nodes[i] points to link list of //nodes with time i LinkList nodes[]; 4

class YieldVolObject extends AbstractFunctionObject { //Yield and volatality are computed for the //bond of that maturity public int maturity; public YieldVolObject() { //call the constructor for the super class super(2); }//end of constructor //If i==0 calculate the yield and otherwise //calculate the vol. Use values as value //of r[t] and k[t] public double evaluate(int i, double val[]) { r[maturity-1]=val[0]; k[maturity-1]=val[1]; if (i==0) { double tempYield =slowYield(0,0,maturity) ; return(tempYield-yield[mat urity-1 ]); } else { double tempVol = slowLogVol(0,0,maturity) ; return(tempVol-volatilitie s[matur ity-1]); } }//end of evaluate }//end of YieldVolObject 5

P oin ts to notice Notice that the class is de�ned YieldV olObje ct � inside the class. T ermStructur e Notice that has complete access YieldV olObje ct � to data of the class. T ermStructur e Nob o dy can access from outside. YieldV olObje ct � 6

JA V A pac k ages W e ha v e or will co v er some classes from the � follo wing pac k ages: (Classes concerned with applets) java.applet { (Classes concerned with GUIs) java.awt { (Classes concerned with I/O) java.io { (Classes concerned with v arious java.util { utilit i es) (Classes concerned with java.net { net w orking) Whole list of pac k ages giv en on page 86-89 in � the b o ok. 7

JA V A I/O pac k age W e co v ered v arious kind of I/O streams. � Ho w to read and write to a �le. � A v ery wide v ariet y of I/O pro vided b y JA V A. � 8

JA V A utlitie s pac k age is in the pac k age. StingTokenizer java.util � Allo ws us to break a line in to tok ens for parsing. � Consider the follo wing fragmen t of co de. � String line=''hhh:xxx:ccc''; StringTokenizer tokenizer = new StringTokenizer(line,'':'') ; String firstToken = tokenizer.nextToken(); String secondToken = tokenizer.nextToken(); 9

Other in teresting classes HashTable � Date � Random � Vector � Stack � Read ab out them on page 527. � 10

pac k age ja v a.lang This pac k age is loaded up b y default . � String , Math , System , are all in this Double � pac k age. and are also de�ned in this Object Exception � pac k age. Read ab out it on page 442. � 11

What is a thread? A is a lik e a program. Thr e ad � Tw o threads run indep enden tly lik e separate � programs. Di�erence is that threads run within a program � and hence can share v ariables. 12

Concurren t Programming Threads enable concurren t programming. � Tw o separate tasks can b e going on in parallel in � a single program. Let us sa y y ou en ter the w ebsite. Blo omb er g � 13

Concurren t Programming (con td) The follo wing tasks can b e going on in parallel: � V arious indexes b eing displa y ed in a b o x. { Hot news tic k er. { Asking the user to en ter a sto c k sym b ol. { All these separate tasks could b e handled b y � separate threads. 14

A small example package threadRelated; public class MyThread extends Thread { public MyThread(String name) { super(name); }//end of MyThread public void run() { for(int i=0; i < 10; i++) { System.out.println(i+" "+getName()); try { sleep((int)Math.random()*1 000); } catch (InterruptedException e) {}; } System.out.println("DONE! "+getName()); }//end of run }//end of MyThread 15

Constructor A thread class extends the JA V A class Thread � de�ned in the pac k age java.lang . The constructor tak es the name of thread as an � argumen t. What do es do? super(name) � 16

metho d run Whenev er a thread is started, metho d is run � called. The metho d in this case go es through the run � lo op times. 10 sleep((int)Math.ran dom() *1000 ) susp ends � the thread for a random time. What is Math.random() ? � gets the name of the thread. getName() � 17

Main Program package threadRelated; public class testMyThread { static public void main(String argv[]) { MyThread thread1 = new MyThread("put"); MyThread thread2 = new MyThread("call"); thread1.start(); thread2.start(); } } 18

Main Program (Con td). There are t w o threads: and thread2 . thread1 � First thread has name and the second one put � call . The metho d on the thread starts the start � thread. 19

When do es a thread stop? A thread stops when either of the follo wing � ev en ts happ en: metho d exits. run { metho d is called on the thread. stop { 20

Output of the program 0 put 0 call 1 call 1 put 2 put 2 call 3 put 3 call 4 put 5 put 4 call 5 call 6 put 6 call 7 put 7 call 8 put 8 call 9 put 9 call DONE! put DONE! call 21

Sync hronization Supp ose that there are t w o threads 1 and 2 T T � that share t w o v ariables and . i j Supp ose eac h thread incremen ts and then i � incremen ts b y the v alue of i . j W e can ha v e t w o sample executions sho wn on � the next slide. 22

Tw o executions Initial value i=1 j=1 First exceution i = i+1 (T1 executes) j = j+i (T2 executes) i = i+1 (T2 executes) j = j+i (T1 exceutes) Second execution i = i+1 (T1 executes) j = j+i (T1 executes) i = i+1 (T2 executes) j = j+i (T2 executes) 23

Inconsistency! First Exc eution � 1 observ es = 6. T j Se c ond Exc eution � 1 observ es = 3. T j Need to con trol access to shared v ariables. � A nswer: Synchronization � 24

T o y T rading System Eac h trader en ters the transaction he/she just � made. A thread reads the transaction record pr o duc er � and puts in a queue. threads read records from the queue Consumer � and log it. 25

T o y T rading Example (Fig) Consumer 1 Consumer 2 log log Trader Queue Producer Figure 1: A T o y T rading System 26

Pro ducer Thread package threadRelated; import java.io.*; public class ProducerThread extends Thread { Queue myQueue; BufferedReader bSystemIn; public ProducerThread(String name, Queue q) { super(name); myQueue = q; bSystemIn = new BufferedReader(new InputStreamReader(System .in)); } public void run() { try { String line; while ((line = bSystemIn.readLine()) != null) { TraderEntry tEntry = new TraderEntry(line); myQueue.add(tEntry); }//end of while } catch (IOException e) { System.err.println("Excepti on occured "+e.getMessage()); } }//end of run } 27

Constructor Constructor tak es: � Name of the thread. { The queue to put things in. { 28

metho d run Reads a line from the screen. � Mak es that line in to a trader-en try . � Adds that trader-en try to the queue. � 29