import java util Hash Set import java util
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![import java. util. Hash. Set; import java. util. Scanner; public class Hash. Set. Example import java. util. Hash. Set; import java. util. Scanner; public class Hash. Set. Example](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-8.jpg)
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![import java. util. Hash. Map; import java. util. Scanner; Δήλωση μιας μεταβλητής Hash. Map import java. util. Hash. Map; import java. util. Scanner; Δήλωση μιας μεταβλητής Hash. Map](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-11.jpg)
![import java. util. Hash. Map; import java. util. Scanner; public class Hash. Map. Example import java. util. Hash. Map; import java. util. Scanner; public class Hash. Map. Example](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-12.jpg)
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![import java. util. Hash. Set; import java. util. Iterator; import java. util. Scanner; public import java. util. Hash. Set; import java. util. Iterator; import java. util. Scanner; public](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-14.jpg)
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![import java. util. Scanner; Υλοποίηση public class Dance. Lesson { public static void main(String[] import java. util. Scanner; Υλοποίηση public class Dance. Lesson { public static void main(String[]](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-19.jpg)
![Μηχανισμός try-throw-catch • Ο κώδικας που μπορεί να δημιουργήσει εξαίρεση μπαίνει σε ένα try-block Μηχανισμός try-throw-catch • Ο κώδικας που μπορεί να δημιουργήσει εξαίρεση μπαίνει σε ένα try-block](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-20.jpg)
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![import java. util. Scanner; Υλοποίηση public class Dance. Lesson { public static void main(String[] import java. util. Scanner; Υλοποίηση public class Dance. Lesson { public static void main(String[]](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-26.jpg)
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![Παράδειγμα public class Division. By. Zero. Exception extends Exception { public Division. By. Zero. Παράδειγμα public class Division. By. Zero. Exception extends Exception { public Division. By. Zero.](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-29.jpg)
![import java. util. Scanner; public class Division. Demo. First. Version { public static void import java. util. Scanner; public class Division. Demo. First. Version { public static void](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-30.jpg)
![import java. util. Scanner; public class Division. Demo. First. Version { public static void import java. util. Scanner; public class Division. Demo. First. Version { public static void](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-31.jpg)
![public static void second. Chance( ) { Scanner keyboard = new Scanner(System. in); System. public static void second. Chance( ) { Scanner keyboard = new Scanner(System. in); System.](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-32.jpg)
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![public class Bad. Number. Exception extends Exception { private int bad. Number; public Bad. public class Bad. Number. Exception extends Exception { private int bad. Number; public Bad.](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-35.jpg)
![import java. util. Scanner; public class Bad. Number. Exception. Demo { public static void import java. util. Scanner; public class Bad. Number. Exception. Demo { public static void](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-36.jpg)
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![public class Negative. Number. Exception extends Exception { public Negative. Number. Exception( ) { public class Negative. Number. Exception extends Exception { public Negative. Number. Exception( ) {](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-38.jpg)
![try { System. out. println("How many pencils do you have? "); int pencils = try { System. out. println("How many pencils do you have? "); int pencils =](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-39.jpg)
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![import java. util. Scanner; public class Division. Demo. Second. Version { public static void import java. util. Scanner; public class Division. Demo. Second. Version { public static void](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-44.jpg)
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![import java. util. Scanner; public class Division. Demo. Second. Version { public static void import java. util. Scanner; public class Division. Demo. Second. Version { public static void](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-46.jpg)
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![import java. util. Scanner; import java. util. Input. Mismatch. Exception; public class Input. Mismatch. import java. util. Scanner; import java. util. Input. Mismatch. Exception; public class Input. Mismatch.](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-49.jpg)
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- Slides: 50
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![import java util Hash Set import java util Scanner public class Hash Set Example import java. util. Hash. Set; import java. util. Scanner; public class Hash. Set. Example](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-8.jpg)
import java. util. Hash. Set; import java. util. Scanner; public class Hash. Set. Example { public static void main(String[] args){ Hash. Set<String> my. Set = new Hash. Set<String>(); Scanner input = new Scanner(System. in); while(input. has. Next()){ String name = input. next(); if (!my. Set. contains(name)){ my. Set. add(name); } } for(String name: my. Set){ System. out. println(name); } Τοποθετούμε στο Hash. Set μόνο τα Strings τα οποία δεν έχουμε ήδη δει (δεν είναι ήδη στο σύνολο) Ένας τρόπος για να διατρέξουμε και να τυπώσουμε τα στοιχεία του Hash. Set Object[] array = my. Set. to. Array(); for (int i = 0; i < array. length; i ++){ String name = (String)array[i]; System. out. println(name); } } } Δήλωση μιας μεταβλητής Hash. Set από Strings. Ένας άλλος τρόπος για να διατρέξουμε το Hash. Set χρησιμοποιώντας την εντολή to. Array(). Ο πίνακας είναι πίνακας από Objects, και πρέπει να κάνουμε downcasting
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![import java util Hash Map import java util Scanner Δήλωση μιας μεταβλητής Hash Map import java. util. Hash. Map; import java. util. Scanner; Δήλωση μιας μεταβλητής Hash. Map](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-11.jpg)
import java. util. Hash. Map; import java. util. Scanner; Δήλωση μιας μεταβλητής Hash. Map που συσχετίζει Strings (κλειδια) και Integers (τιμές) Για κάθε όνομα (String) το id (Integer) public class Hash. Map. Example 1 { public static void main(String[] args){ Hash. Map<String, Integer> my. Map = new Hash. Map<String, Integer>(); Scanner input = new Scanner(System. in); int counter = 0; while(input. has. Next()){ String name = input. next(); if (!my. Map. contains. Key(name)){ my. Map. put(name, counter); counter ++; } } Διατρέχοντας το Hash. Map Αν το όνομα δεν είναι ήδη στο Hash. Map τότε ανάθεσε στο όνομα αυτό τον επόμενο αύξοντα αριθμό και πρόσθεσε ένα νέο ζευγάρι (όνομα αριθμός) στο Hash. Map. Διέτρεξε το σύνολο με τα κλειδιά (ονόματα) στο Hash. Map for(String name: my. Map. key. Set()){ System. out. println(name + ": "+ my. Map. get(name)); } } } Για κάθε κλειδί (όνομα) πάρε το id που αντιστοιχεί στο όνομα αυτό και τύπωσε το.
![import java util Hash Map import java util Scanner public class Hash Map Example import java. util. Hash. Map; import java. util. Scanner; public class Hash. Map. Example](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-12.jpg)
import java. util. Hash. Map; import java. util. Scanner; public class Hash. Map. Example 2 { public static void main(String[] args){ Hash. Map<String, Person> my. Map = new Hash. Map<String, Person>(); Scanner input = new Scanner(System. in); int counter = 0; while(input. has. Next()){ String name = input. next(); if (!my. Map. contains. Key(name)){ Person p = new Person(name, counter); my. Map. put(name, p); counter ++; Δημιουργούμε ένα Hash. Map το οποίο } σε κάθε διαφορετικό όνομα αντιστοιχεί } ένα αντικείμενο Person. for(String name: my. Map. key. Set()){ System. out. println(my. Map. get(name)); } } } Καλείται η to. String της κλάσης Person
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![import java util Hash Set import java util Iterator import java util Scanner public import java. util. Hash. Set; import java. util. Iterator; import java. util. Scanner; public](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-14.jpg)
import java. util. Hash. Set; import java. util. Iterator; import java. util. Scanner; public class Iterator. Example { public static void main(String[] args){ Hash. Set<String> my. Set = new Hash. Set<String>(); Scanner input = new Scanner(System. in); while(input. has. Next()){ if (!my. Set. contains(name)){ my. Set. add(input. next()); } } Διατρέχει το σύνολο και αν βρει το Iterator it = my. Set. iterator(); String “a” το αφαιρεί από το σύνολο. while (it. has. Next()){ if (it. next(). equals("a")){ it. remove(); Πρέπει να κάνουμε break γιατί αν break; αφαιρέσουμε μία τιμή ενώ διατρέχουμε το } σύνολο μπορεί να προκληθεί λάθος. } it = my. Set. iterator(); Ξανα-διατρέχουμε τον πίνακα. while (it. has. Next()){ Ο iterator πρέπει να ξανα-οριστεί για System. out. println(it. next()); να ξεκινήσει από την αρχή του } } } συνόλου.
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![import java util Scanner Υλοποίηση public class Dance Lesson public static void mainString import java. util. Scanner; Υλοποίηση public class Dance. Lesson { public static void main(String[]](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-19.jpg)
import java. util. Scanner; Υλοποίηση public class Dance. Lesson { public static void main(String[] args) { Scanner keyboard = new Scanner(System. in ); System. out. println("Enter number of male and female dancers: "); int men = keyboard. next. Int (); int women = keyboard. next. Int(); if (men == 0 && women == 0 ){ System. out. println("Lesson is canceled. No students. "); System. exit(0); }else if (men == 0){ System. out. println("Lesson is canceled. No men. "); System. exit(0); }else if (women == 0){ System. out. println("Lesson is canceled. No women. "); System. exit(0); } if (women >= men) System. out. println("Each man must dance with " + women/(double)men + " women. "); else System. out. println("Each woman must dance with " + men/(double)women + " men. "); System. out. println("Begin the lesson. "); } } χωρίς εξαιρέσεις
![Μηχανισμός trythrowcatch Ο κώδικας που μπορεί να δημιουργήσει εξαίρεση μπαίνει σε ένα tryblock Μηχανισμός try-throw-catch • Ο κώδικας που μπορεί να δημιουργήσει εξαίρεση μπαίνει σε ένα try-block](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-20.jpg)
Μηχανισμός try-throw-catch • Ο κώδικας που μπορεί να δημιουργήσει εξαίρεση μπαίνει σε ένα try-block • Αν η εξέλιξη του κώδικα είναι προβληματική εκτελείται η εντολή throw η οποία «πετάει» την εξαίρεση • Αν υπάρξει εξαίρεση η ροή του κώδικα μεταφέρεται στο catch-block το οποίο χειρίζεται τις εξαιρέσεις try { if (men == 0 && women == 0) throw new Exception("No students. Νο Lesson. "); else if (men == 0) throw new Exception("No men. Νο Lesson. "); else if (women == 0) throw new Exception("No women. Νο Lesson. "); if (women >= men) System. out. println("Each man must dance with " + women/(double)men + " women. "); else System. out. println("Each woman must dance with " + men/(double)women + " men. "); } catch(Exception e) { String message = e. get. Message( ); System. out. println(message); System. exit(0); }
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![import java util Scanner Υλοποίηση public class Dance Lesson public static void mainString import java. util. Scanner; Υλοποίηση public class Dance. Lesson { public static void main(String[]](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-26.jpg)
import java. util. Scanner; Υλοποίηση public class Dance. Lesson { public static void main(String[] args) { Scanner keyboard = new Scanner(System. in ); System. out. println("Enter number of male and female dancers: "); int men = keyboard. next. Int (); int women = keyboard. next. Int(); try{ if (men == 0 && women == 0) throw new Exception("Lesson is canceled. No students. "); else if (men == 0) throw new Exception("Lesson is canceled. No men. "); else if (women == 0) throw new Exception("Lesson is canceled. No women. "); if (women >= men) System. out. println("Each man must dance with " + women/(double)men + " women. "); else System. out. println("Each woman must dance with " + men/(double)women + " men. "); } catch(Exception e ){ String message = e. get. Message( ); System. out. println(message); System. exit(0); } System. out. println("Begin the lesson. "); } } με εξαιρέσεις
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![Παράδειγμα public class Division By Zero Exception extends Exception public Division By Zero Παράδειγμα public class Division. By. Zero. Exception extends Exception { public Division. By. Zero.](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-29.jpg)
Παράδειγμα public class Division. By. Zero. Exception extends Exception { public Division. By. Zero. Exception( ) { super("Division by Zero!"); } public Division. By. Zero. Exception(String message) { super(message); } } Η κλάση κληρονομεί και την μέθοδο get. Message()
![import java util Scanner public class Division Demo First Version public static void import java. util. Scanner; public class Division. Demo. First. Version { public static void](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-30.jpg)
import java. util. Scanner; public class Division. Demo. First. Version { public static void main(String[] args) { try { Scanner keyboard = new Scanner(System. in); System. out. println("Enter numerator: "); int numerator = keyboard. next. Int(); System. out. println("Enter denominator: "); int denominator = keyboard. next. Int(); if (denominator == 0) throw new Division. By. Zero. Exception( ); double quotient = numerator/(double)denominator; System. out. println(numerator + "/" + denominator + " = " + quotient); } catch(Division. By. Zero. Exception e) { System. out. println(e. get. Message( )); system. Exit(0); } System. out. println("End of program. "); } }
![import java util Scanner public class Division Demo First Version public static void import java. util. Scanner; public class Division. Demo. First. Version { public static void](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-31.jpg)
import java. util. Scanner; public class Division. Demo. First. Version { public static void main(String[] args) { try { Scanner keyboard = new Scanner(System. in); System. out. println("Enter numerator: "); int numerator = keyboard. next. Int(); System. out. println("Enter denominator: "); int denominator = keyboard. next. Int(); if (denominator == 0) throw new Division. By. Zero. Exception( ); double quotient = numerator/(double)denominator; System. out. println(numerator + "/" + denominator + " = " + quotient); } catch(Division. By. Zero. Exception e) { System. out. println(e. get. Message( )); second. Chance( ); } System. out. println("End of program. "); } } Μπορούμε μέσα στο catch block να καλούμε μία άλλη μέθοδο
![public static void second Chance Scanner keyboard new ScannerSystem in System public static void second. Chance( ) { Scanner keyboard = new Scanner(System. in); System.](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-32.jpg)
public static void second. Chance( ) { Scanner keyboard = new Scanner(System. in); System. out. println("Try again: "); System. out. println("Enter numerator: "); int numerator = keyboard. next. Int(); System. out. println("Enter denominator: "); System. out. println("Be sure the denominator is not zero. "); int denominator = keyboard. next. Int(); if (denominator == 0) { System. out. println("I cannot do division by zero. "); System. out. println("Aborting program. "); System. exit(0); } double quotient = ((double)numerator)/denominator; System. out. println(numerator + "/" + denominator + " = " + quotient); } }
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![public class Bad Number Exception extends Exception private int bad Number public Bad public class Bad. Number. Exception extends Exception { private int bad. Number; public Bad.](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-35.jpg)
public class Bad. Number. Exception extends Exception { private int bad. Number; public Bad. Number. Exception(int number) { super("Bad. Number. Exception"); bad. Number = number; } public Bad. Number. Exception( ) { super("Bad. Number. Exception"); } public Bad. Number. Exception(String message) { super(message); } public int get. Bad. Number( ) { return bad. Number; } }
![import java util Scanner public class Bad Number Exception Demo public static void import java. util. Scanner; public class Bad. Number. Exception. Demo { public static void](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-36.jpg)
import java. util. Scanner; public class Bad. Number. Exception. Demo { public static void main(String[] args) { try { Scanner keyboard = new Scanner(System. in); System. out. println("Enter year of birth: "); int input. Number = keyboard. next. Int(); if (input. Number > 2013) throw new Bad. Number. Exception(input. Number); System. out. println("Thank you for entering " + input. Number); } catch(Bad. Number. Exception e) { System. out. println(e. get. Bad. Number( ) + " is not valid. "); } System. out. println("End of program. "); } } Μας επιστρέφει τον αριθμό που προκάλεσε την εξαίρεση
![](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-37.jpg)
![public class Negative Number Exception extends Exception public Negative Number Exception public class Negative. Number. Exception extends Exception { public Negative. Number. Exception( ) {](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-38.jpg)
public class Negative. Number. Exception extends Exception { public Negative. Number. Exception( ) { super("Negative Number Exception!"); } public Negative. Number. Exception(String message) { super(message); } }
![try System out printlnHow many pencils do you have int pencils try { System. out. println("How many pencils do you have? "); int pencils =](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-39.jpg)
try { System. out. println("How many pencils do you have? "); int pencils = keyboard. next. Int(); if (pencils < 0) throw new Negative. Number. Exception("pencils"); System. out. println("How many erasers do you have? "); int erasers = keyboard. next. Int(); double pencils. Per. Eraser; if (erasers < 0) throw new Negative. Number. Exception("erasers"); else if (erasers != 0) pencils. Per. Eraser = pencils/(double)erasers; else throw new Division. By. Zero. Exception( ); System. out. println("Each eraser must last through " + pencils. Per. Eraser + " pencils. "); } catch(Negative. Number. Exception e) { System. out. println("Cannot have a negative number of " + e. get. Message( )); } catch(Division. By. Zero. Exception e) { System. out. println("Do not make any mistakes. "); }
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![import java util Scanner public class Division Demo Second Version public static void import java. util. Scanner; public class Division. Demo. Second. Version { public static void](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-44.jpg)
import java. util. Scanner; public class Division. Demo. Second. Version { public static void main(String[] args) { Scanner keyboard = new Scanner(System. in); try { System. out. println("Enter numerator: "); int numerator = keyboard. next. Int(); System. out. println("Enter denominator: "); int denominator = keyboard. next. Int(); Εφόσον έχουμε μία μέθοδο που πετάει εξαίρεση, θα πρέπει να τη βάλουμε μέσα σε try-catch block double quotient = safe. Divide(numerator, denominator); System. out. println(numerator + "/" + denominator + " = " + quotient); } catch(Division. By. Zero. Exception e) { System. out. println(e. get. Message( )); System. exit(0); } System. out. println("End of program. "); } Η εξαίρεση δημιουργείται στην safe. Divide αλλά την πιάνουμε και την χειριζόμαστε στην main public static double safe. Divide(int top, int bottom) throws Division. By. Zero. Exception { if (bottom == 0) throw new Division. By. Zero. Exception( ); return top/(double)bottom; } }
![](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-45.jpg)
![import java util Scanner public class Division Demo Second Version public static void import java. util. Scanner; public class Division. Demo. Second. Version { public static void](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-46.jpg)
import java. util. Scanner; public class Division. Demo. Second. Version { public static void main(String[] args) { Scanner keyboard = new Scanner(System. in); try { System. out. println("Enter numerator: "); int numerator = keyboard. next. Int(); System. out. println("Enter denominator: "); int denominator = keyboard. next. Int(); Εφόσον έχουμε δεν πετάει εξαίρεση, θα πρέπει να τη βάλουμε μέσα σε trycatch block int percentage = safe. Percentage(numerator, denominator); System. out. println("percentage = " + percentage +"%"); } catch(Division. By. Zero. Exception e) { System. out. println(e. get. Message( )); System. exit(0); } System. out. println("End of program. "); } Η safe. Percentage δεν χρειάζεται try-catch block γιατί πετάει κι αυτή την εξαίρεση της safe. Divide (declare) public static int safe. Percentage(int top, int bottom) throws Division. By. Zero. Exception { double ratio = safe. Divide(top, bottom); return (int)(ratio*100); } public static double safe. Divide(int top, int bottom) throws Division. By. Zero. Exception { if (bottom == 0) throw new Division. By. Zero. Exception( ); return top/(double)bottom; } }
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![](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-48.jpg)
![import java util Scanner import java util Input Mismatch Exception public class Input Mismatch import java. util. Scanner; import java. util. Input. Mismatch. Exception; public class Input. Mismatch.](https://slidetodoc.com/presentation_image_h/2f8df84b4a5096743a191fe6338edf55/image-49.jpg)
import java. util. Scanner; import java. util. Input. Mismatch. Exception; public class Input. Mismatch. Exception. Demo { public static void main(String[] args) { Scanner keyboard = new Scanner(System. in); int number = 0; //to keep compiler happy boolean done = false; while (! done) { try { System. out. println("Enter a whole number: "); number = keyboard. next. Int(); done = true; } catch(Input. Mismatch. Exception e) { keyboard. next. Line(); System. out. println("Not a correctly written whole number. "); System. out. println("Try again. "); } } System. out. println("You entered " + number); } }
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