MAS-02-en [tryb zgodności] - pjwstk

Castingo Why?o An examplevoid casts( ) {int i = 200;long l = (long)i;long l2 = (long)200;}Design and Analysis of Information Systems (MAS), lecture 02 12

o IfA Control Flowif(Boolean-expression)statementelsestatemento returno Iterationwhile(Boolean-expression)statementDesign and Analysis of Information Systems (MAS), lecture 02 13

o do-whiledostatementA Control Flow (2)while(Boolean-expression);o break, continueo forfor(initialization; Booleanexpression;step)statementDesign and Analysis of Information Systems (MAS), lecture 02 14

A Control Flow (3)o switchswitch(integral-selector) {}case integral-value1 : statement; break;case integral-value2 : statement; break;case integral-value3 : statement; break;case integral-value4 : statement; break;case integral-value5 : statement; break;// ...default: statement;Design and Analysis of Information Systems (MAS), lecture 02 15

InterfacesooA purposeAn exampleinterface Instrument {// A constant:// static & finalint I = 5;// Declaration only// a public methodvoid play(Note n);String what();}void adjust();Design and Analysis of Information Systems (MAS), lecture 02 16

Interfaces(2)oImplementation of the interfaceclass Wind implements Instrument {// windpublic void play(Note n) {System.out.println("Wind.play() " + n);}public String what() { return "Wind"; }public void adjust() {}}class Brass extends Wind {public void play(Note n) {System.out.println("Brass.play() " + n);}public void adjust() {System.out.println("Brass.adjust()");}}class Woodwind extends Wind {public void play(Note n) {System.out.println("Woodwind.play() " + n);}public String what() { return "Woodwind"; }}Design and Analysis of Information Systems (MAS), lecture 02 17

o Errors:l Compilation time,l Runtimeo Old approachesErrors handlingl A special global variable,l Returning a special value (which one?)o The current approach – exceptionsl Prosl Cons (?)Design and Analysis of Information Systems (MAS), lecture 02 19

o The classExceptionso Inheritance from the Exception classo Attributeso Catching and processingtry {// a code which may cause n exception} catch(Type1 id1) {// processing of the exception Type1} catch(Type2 id2) {// processing of the exception Type2}Design and Analysis of Information Systems (MAS), lecture 02 20

Exceptions (2)o A method which does not throw exceptionsoutside but processes them insidevoid f( ) { // ...o A method which warns that it may throw anexceptionvoid f( ) throws TooBigException,DivZeroException{ //...o Which approach is better?Design and Analysis of Information Systems (MAS), lecture 02 21

Exceptions (3)o Catching all exceptionscatch(Exception e) {System.err.println("Caught an exception");}o Rethrowing the exceptioncatch(Exception e) {System.err.println("An exception was thrown");throw e;}o Special case: NullPointerExceptionperson.showName();Design and Analysis of Information Systems (MAS), lecture 02 22

Exceptions (4)o Cleaining up with finallytry {// „Suspicious region”: we expect some exceptions:// A, B or C} catch(A a1) {// processing for A} catch(B b1) {// processing for B} catch(C c1) {// processing for C} finally {}// processed every time!Design and Analysis of Information Systems (MAS), lecture 02 23

o Different needsllConstants’ UtilizationA constant value (i.e. a iteration number)A classification of different items• Old-school solution (not recommended!)public class MainMenu {}public static final int MENU_FILE = 0;public static final int MENU_EDIT = 1;public static final int MENU_FORMAT = 2;public static final int MENU_VIEW = 3;• A new apporach (enum type)public enum MainMenu {FILE, EDIT, FORMAT, VIEW};Design and Analysis of Information Systems (MAS), lecture 02 24

To be continued…Design and Analysis of Information Systems (MAS), lecture 02 25