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Qwizdom : Basic Java review

Qwizdom : Basic Java review. Chris Loftus. Which of the following signatures are valid for the main() method entry point of an application?. public static void main() public static void main(String arg []) public void main(String [] arg ) public static void main(String [] args )

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Qwizdom : Basic Java review

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  1. Qwizdom: Basic Java review Chris Loftus

  2. Which of the following signatures are valid for the main() method entry point of an application? • public static void main() • public static void main(String arg[]) • public void main(String [] arg) • public static void main(String [] args) • public static int main(String [] arg)

  3. Study the following class diagram.The multiplicity constraint 0..* on the association between MUDGame and Treasure means (choose one): Player --------------------- -String name -intpowerPoints -Treasure[] booty -Image image --------------------- +void takeTurn() MUDGame --------------------- -Player[] players -Treasure[] treasures --------------------- +void run() 0..* • A MUDGame class is connected to many Treasure classes • An object of class Treasure may be connected to zero or many MUDGame objects • An object of class MUDGame may be connected to zero or many Treasure objects • A Treasure class is connected to many MUDGame classes 0..* Treasure --------------------- -String specialPower -Image image --------------------- +void applyPower() 0..* 1..1 Image --------------------- -String filename 1..1

  4. Consider the following line of code:int x[] = new int[25];After execution, which statement or statements is/are true? • x[24] is 0 • x[24] is undefined • x[25] is 0 • x[0] is null • x.length is 25

  5. Consider the following application: 1. class HolderApp { 2. public static void main(String args[]){ 3. Holder h = new Holder(); 4. h.held = 100; 5. h.bump(h); 6. System.out.println(h.held); 7. } 8. } 9. class Holder {10. public int held;11. public void bump(Holder theHolder){12. theHolder.held++;13. }14. }What value is printed out at line 6? • 0 • 1 • 100 • 101

  6. Study the following class diagram.The multiplicity constraint 1..1 on the association between Treasure and Image means (choose one): Player --------------------- -String name -intpowerPoints -Treasure[] booty -Image image --------------------- +void takeTurn() MUDGame --------------------- -Player[] players -Treasure[] treasures --------------------- +void run() 0..* • An object of class Treasure must be connected to one Image class • An object of class Treasure may be connected to one Image object • An object of class Treasure must be connected to one object of class Image 0..* Treasure --------------------- -String specialPower -Image image --------------------- +void applyPower() 0..* 1..1 Image --------------------- -String filename 1..1

  7. Study the following class diagram.The constraint “-” before String specialPowermeans (choose one): Treasure --------------------- -String specialPower -Image image --------------------- +void applyPower() • The attribute specialPower is private to the Treasure class • The attribute specialPower is public to all classes • The attribute specialPower is protected within the Treasure class

  8. Consider the following application: 1. class DecrementerApp{ 2. public static void main(String args[]){ 3. double d = 12.3; 4. Decrementerdec = new Decrementer(); 5. dec.decrement(d); 6. System.out.println(d); 7. } 8. } 9. class Decrementer{10. public void decrement(double decMe){11. decMe = decMe – 1;12. }13. }What value is printed out at line 6? • 0.0 • -1.0 • 12.3 • 11.3

  9. After execution of the code fragment below, what are the values of the variables x, a, and b?1. int x, a = 6, b = 7;2. x = a++ + b++; • x = 15, a = 7, b = 8 • x = 15, a = 6, b = 7 • x = 13, a = 7, b = 8 • x = 13, a = 6, b = 7

  10. Quiz: How many times does this loop execute? int n = 10; for (int i=0; i<=n; i++){ // statements here } • 10 times • Only once since i is only incremented once • 11 times • 0 times, since i is given the value 0 • It never stops

  11. Quiz: How many times does this loop execute? int n = 10; for (int i=0; i<n; i--){ // statements here } • 10 times • Only once since i is only incremented once • 11 times • 0 times, since i is given the value 0 • It only stops when i has value -2147483648

  12. Study the following code fragment:1. String [] names = { “Fred”, “Jim”, “Sheila” };2. for (inti=0; i <= names.length; i++){3. System.out.print(names[i] + “ – “);4. } What output results when this code fragment is run? (Choose one) • An ArrayIndexOutOfBoundsException is thrown at line 3 • Fred – Jim – Sheila – ArrayIndexOutOfBoundsException thrown at line 3 • Fred – Jim – Sheila -

  13. What results from the following fragment of code?1. int x = 1;2. String [] names = { “Fred”, “Jim”, “Sheila” };3. names[--x] += “.”;4. for (inti=0; i < names.length; i++){5. System.out.println(names[i]);6. }Choose one answer. • The output includes Fred. with the trailing full stop • The output includes Jim. with the trailing full stop • The output includes Sheila. with the trailing full stop • None of the outputs shows a trailing full stop • An ArrayIndexOutOfBoundsException is thrown

  14. Lab: Basic Java all tasks

  15. Study the following class diagram.What is the meaning of the relationship between Employee and Manager? (choose one): Employee • Employee extends Manager • Employee implements Manager • Manager implements Employee • Manager extends Employee Manager

  16. Which one statement is true about the following code fragment?1. int j = 2; 2. switch (j) { 3. case 2: 4. System.out.println(“value is two”); 5. case 3: 6. System.out.println(“value is three”); 7. break; 8. default: 9. System.out.println(“value is “ + j);10. break;11. } • The code will not compile because case 2 is missing a break statement • The output would be only the text valueis two • The output would be the text value is two followed by the text value is three • The output would be the text value is two, followed by the text value is three, followed by the text value is 2

  17. Quiz: What is printed if the user types in “one”? String answer = in.next(); switch (answer.charAt(0)){ case ‘o’: System.out.println(“Typed one”); case ‘t’: System.out.println(“Typed two or three”); break; default: System.out.println(“Something else”); } • Typed one • Typed two or three • Something else • None of the above

  18. Study the following class diagram.The constraint “+” before void applyPower() means (choose one): Treasure --------------------- -String specialPower -Image image --------------------- +void applyPower() • The attribute applyPower is public to all classes • The method applyPower is public to all classes • The method applyPower is protected within the Treasure class • The attribute applyPower is protected within the Treasure class

  19. Study the following class diagram.What is the meaning of the relationship between Employee and Manager? (choose one): <<interface>> Employee • Employee extends Manager • Employee implements Manager • Manager implements Employee • Manager extends Employee Manager

  20. Quiz: When should we use a collection such as ArrayList? (Choose the most accurate answer) • When we have a fixed number of data items to store in an object • When we have a variable and unknown number of items to store in an object • When we want to make our code more flexible

  21. Quiz: arrayList.add(“value”) inserts “value” at the start of arrayList. TRUE or FALSE?

  22. Consider this class:1. public class Test1 { 2. public float aMethod(float a, float b) { 3. return 0.0F; 4. } 5. 6. }Which of the following methods would be legal if added (individually) at line 5? • public intaMethod(int a, int b) {return 0;} • public float aMethod(float a, float b) {return 0.0F;} • public float aMethod(float a, float b, int c) {return 0.0F;} • public float aMethod(float c, float d) {return 0.0F;} • private float aMethod(int a, int b, int c) {return 0.0F;}

  23. Consider the following fragment of code:1. try { 2. runMethod(); 3. } 4. catch(IOExceptionioe){ 5. System.out.println(“IOException thrown”); 6. } 7. catch(FileNotFoundExceptionfnfe){ 8. System.out.println(“FileNotFoundException thrown”); 9. }10. catch(Exception e){11. System.out.println(“Exception thrown”); 12. }13. finally {14. System.out.println(“In finally”); 15. }What output results when runMethod completes without throwing an exception? (Choose one) • The string In finally is displayed • Nothing is displayed

  24. Consider the following fragment of code:1. try { 2. runMethod(); 3. } 4. catch(IOExceptionioe){ 5. System.out.println(“IOException thrown”); 6. } 7. catch(FileNotFoundExceptionfnfe){ 8. System.out.println(“FileNotFoundException thrown”); 9. }10. catch(Exception e){11. System.out.println(“Exception thrown”); 12. }13. finally {14. System.out.println(“In finally”); 15. }What output results when runMethod throws ClassCastException? (Choose one) • The string Exception thrown followed by In finally are displayed • The string Exception thrown is display • All the above messages from lines 5, 8,11 and 14 are displayed

  25. Consider the following fragment of code:1. try { 2. runMethod(); 3. } 4. catch(Exception ioe){ 5. System.out.println(“Exception thrown”); 6. } 7. catch(FileNotFoundExceptionfnfe){ 8. System.out.println(“FileNotFoundException thrown”); 9. }10. catch(IOException e){11. System.out.println(“IOException thrown”); 12. }13. finally {14. System.out.println(“In finally”); 15. }What output results when runMethod throws IOException? (Choose one) • The string IOException thrown followed by In finally are displayed • The string Exception thrown followed by In finally are displayed • The string IOException thrown is display • All the above messages from lines 5, 8,11 and 14 are displayed

  26. Consider this method:1. public void readKeyboard(){2. Scanner in = new Scanner(System.in);3. System.out.print("enter license: ");4. licenseNumber = in.next();5. }When called, this method will do the following (choose the most accurate)? • Create a Scanner object that will read text from a file, and will on line 4 read text until a whitespace character is reached and will return that text as a String • Create a Scanner object that will read text from the standard input (probably the keyboard), and will on line 4 read text until a whitespace character is reached and will return that text as a String • Create a Scanner object that will read text from the standard input (probably the keyboard), and will on line 4 read text until a whitespace character is reached and will return that text as an int

  27. Consider the following classes, declared in separate source files:1. public class Base { 2. public void meth(inti){ 3. System.out.print(“Value is “ + i + “ - “); 4. } 1. public class Sub extends Base { 2. public void meth(int j){ 3. System.out.print(“This value is “ + j + “ - “); 4. } 5. public static void main(String args[]){ 6. Base b1 = new Base(); 7. Base b2 = new Sub(); 8. b1.meth(5); 9. b2.meth(6);10. }11. }What output results when the main method of the class Sub is run? (Choose one) • Value is 5 - Value is 6 • This value is 5 - This value is 6 • Value is 5 - This value is 6 • This value is 5 - Value is 6

  28. Quiz: What is printed if the user types in “three”? String answer = in.next(); switch (answer){ case “one”: System.out.println(“Typed one”); break; case “two”: case “three”: System.out.println(“Typed two or three”); break; default: System.out.println(“Something else”); } • Typed one • Typed two or three • Something else • None of the above

  29. for (Person p: people) { System.out.println(p); } Consider the following code and design. What will be displayed? Person ----------------------- -String name etc ----------------------- +toString(): String 0..* Application ----------------------- -people: Person[] This will not compile Zero or many Person details An incomprehensible set of characters representing objects

  30. Lab: Basics: Times and Clocks

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