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Review

Review. 1. How many primitive data types in Java?. 6 8 10 12. 2, After execution of the code fragment below, what are the values of the variables result, a, and b? int result, a=10,b=11; result=( a++ + b--)%5;. result= 3, a = 11, b = 10 result= 2, a = 10, b = 11

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Review

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  1. Review

  2. 1. How many primitive data types in Java? • 6 • 8 • 10 • 12

  3. 2, After execution of the code fragment below, what are the values of the variables result, a, and b? int result, a=10,b=11;result=( a++ + b--)%5; • result= 3, a = 11, b = 10 • result= 2, a = 10, b = 11 • result= 1, a = 11, b = 10 • result= 1, a = 11, b = 11

  4. 3. After execution of the code fragment below, what are the values of the variables result, a, and b? int result, a=10,b=11; result = ((++a) > b) ? a : b; • result= 11, a = 11, b = 11 • result= 0, a = 11, b = 11 • result= 10, a = 11, b = 11 • result= 11, a = 10, b = 11

  5. 4. A statement for a constructor that invokes the no-args, default constructor in its superclass is: • this.constructor(); • descendent classes can not call constructors of their superclass. • This • super();

  6. The program has a syntax error because Test does not have a default constructor. • The program has a syntax error because x has not been initialized. • The program has a syntax error because you cannot create an object from the class that defines the object. • The program has a syntax error because System.out.println method cannot be invoked from the constructor.

  7. 6. Assume class A extends class B, that is, class A is defined as: class A extends B { .... }// end of class A Which class is the super class and which one is the subclass? • B is both the super class and subclass • B is the super class, A is the subclass • A is both the super class and subclass • A is the super class, B is the subclass

  8. 7. Choose the 1 item below that is not typically listed as a major component of object oriented languages: • Polymorphism • Inheritance • Abstraction • Encapsulation

  9. 8. Choose the best answer. What is created by lines 6-9 of the Point3D subclass? 3: public class Point3D extends Point { 4: public int z; 5: 6: public Point3D(int x, int y, int z) { 7: super(x,y); 8: this.z = z; 9: } • constructor method • method to extend Point3D • new method called Point3D

  10. 9. What does the following code do? double a=Double.parseDouble(new String ("12.566")); • Converts the double 12.566 into a string with the text 12.566 • Syntax Error • Converts a string with the text 12.566 into an double with the value 12 • Converts a string with the text 12.566 into an double with the value 12.566

  11. 10. What is about constructor? • it has the same name as the class • it does not return a value • it has void • it often sets the initial values of instance variables

  12. 11. What is about overloading? • Method overloading is the process of using the same method name for multiple methods • The signature of each overloaded method must be unique  • The signature includes the number, type, and order of the parameters • Constructors can not be overloaded

  13. 12. Assume s = " aa bb ccdd efg kh "; What's the value of count after this while loop? int count=0;StringTokenizer tokenizer = new StringTokenizer (s); while (tokenizer.hasMoreTokens()) { count++; tokenizer.nextToken(); } • 5 • 6 • 7 • 8

  14. 13. What is about Static modifier? • Static variables are sometimes called class variables • The static modifier can be applied to variables as well • Static methods cannot reference instance variables, because instance variables don't exist until an object exists • The static modifier can not be applied to variables

  15. 14. What is about Overriding? • Overriding deals with two methods, one in a parent class and one in a child class, that have the same signature • Overriding deals with two methods, one in a parent class and one in a child class, that have the diferrent signature • Overriding l deals with two methods in the same Class • Overriding lets you define a similar operation in different ways for different object types

  16. 15. Which correctly creates an array of five empty Strings? • String[] a = new String [5]; • String[] a = {"", "", "", "", ""}; • String[5] a; • String[ ] a = new String [5]; for (int i = 0; i < 5; a[i++] = null;

  17. 16. which of the following are valid identifiers? • _id • $id • #id • -id

  18. 17. which of the following are characteristic of a fully encapsulated class? • all variables are private • all methods are private • methods are provided to access the class's properties • the class's design may be changed with minimal impact on its implementation

  19. 18. Which of these are valid declaration of the main() method? • public void main(String args[]) {/* … */} • static void main(String args[]) {/* … */} • public static int main(String args[]) {/* … */} • final static public void main(String[] arguments) {/* … */}

  20. 19. which of the following is not a wrapper class? • String • Integer • Boolean • character

  21. 20. Which three are valid declarations of a float? (Choose three.) • float foo = -1; • float foo = 1.0; • float foo = 42el; • float foo = 2.02f; • float foo = 3.03d; • float foo = 0x0123;

  22. 21. Which two are legal String declarations? (Choose two.) • String s = null; • String s = 'null'; • String s = (String)'abc'; • String s = "This is a string";

  23. 22. Which two are valid declarations of a float? (Choose two.) • float f = 1F; • float f = 1.0; • float f = '1'; • float f = "1"; • float f = 1.0d;

  24. 23. Which two are valid declarations of a boolean? (Choose two.) • boolean b = 0; • boolean b = true; • boolean b = "true"; • boolean b = 'true'; • boolean b = (3 >= 0); • boolean b = Boolean.TRUE;

  25. 24. Given:11. Object objA = new Object();12. Object objB = new Object();13. Object objC = objA;Which two evaluate to true? (Choose two.) • objA == objB • objC == objA • objB == objC • objA.equals(objC) • objB.equals(objA)

  26. 25. Given:11. String s = "Hello" + 9 + 1;12 System.out.println(s);What is the result? • Hello91 • Hello10 • Compilation fails. • An exception is thrown at runtime.

  27. 26. Given:21. int i = 1;22. int j = i++;23. if((i == ++j) | (i++ == j)) {24. i += j;25. }26. System.out.println("i = " + i);What is the result? • i = 1 • i = 2 • i = 3 • i = 4 • i = 5

  28. 27. Given:11. int i = 0, j = 1;12. if((i++ == 0) || (j++ == 2)) {13. i = 42;14. }15. System.out.println("i = " + i + ", j = " + j);What is the result? • i = 1, j = 2 • i = 1, j = 1 • i = 42, j = 2 • i = 42, j = 1

  29. 28. Which two demonstrate encapsulation of data? (Choose two.) • Methods are protected. • Instance variables are private. • Instance variables have default access. • Instance variables can be modified directly. • Instance variables are accessed and modified only through methods.

  30. 29. Given "B is a D" and "B has a C," which two statements are true? (Choose two.) • D refers to C. • B refers to C. • D inherits from B. • B inherits from D

  31. 30. Which modifier, when applied to instance variable, breaks encapsulation? • void • final • public • static • private

  32. Finish

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