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OXUS20 JAVA Programming Questions and Answers PART I
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OXUS20 JAVA Programming Questions and Answers PART I

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OXUS 20 is pleased to offer PART I of Java Programming Questions and Answers with details explanation to support the educational needs and hoping these series help and benefit Computer Science …

OXUS 20 is pleased to offer PART I of Java Programming Questions and Answers with details explanation to support the educational needs and hoping these series help and benefit Computer Science student, IT professionals and those who eager to learn programming and in particular Java Programming...

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  • 1. https://www.facebook. com/Oxus20 PART I – Single and Multiple choices, True/False and Blanks: 1) ............. If I have a variable that is a constant, then I must define the variable name with capital letters.  True  False  False - Because you don't have to define the constant variable name with CAPITAL; but it is recommended. 2) If you forget to put a closing quotation mark on a string, what kind error will be raised?  A compilation error  A runtime error  A logic error 3) ............. What is the size of a char?  4 bits  8 bits  7 bits  16 bits  16 bits - Because the char data type is a single 16-bit Unicode character. It has a minimum value of 'u0000' (or 0) and a maximum value of 'uFFFF' (or 65,535 inclusive). 4) If a program compiles fine, but it produces incorrect result, then the program suffers __________.  A compilation error A logic error -  A runtime error Because the program compiles fine, also there is no Runtime Error because the program does not crush.  A logic error 5) Which of the following are the reserved words?  public  static  void  class Abdul Rahman Sherzad All of them are Reserved Words (Key Words) in JAVA. Page 1 of 11
  • 2. https://www.facebook. com/Oxus20 6) ............. The operator, +, may be used to concatenate strings together as well as add two numeric quantities together.  True  False  True - Because: String full_name = "Abdul Rahman " + "Sherzad"; int sum = 2 + 3; 7) Analyze the following code. public class Test { public static void main(String[] args) { System.out.println(myMethod(2)); } public static int myMethod(int num) { return num; } public static void myMethod(int num) { System.out.println(num); } }  The program has a compile error because the two methods myMethod have the same signature.  The program has a compile error because the second myMethod method is defined, but not invoked in the main method.  The program runs and prints 2 once.  The program runs and prints 2 twice. The method name and parameter list are part of method signature. Declaration of two methods with same signature is not possible because The Java compiler is able to distinguish the difference between the methods through their method signatures. 8) Math.pow(4, 1 / 2) returns __________. 2  2.0 0  0.0 1  1.0  1.O – Because:  1 / 2 = 0 due to the INTEGER Division  Math.pow(4, 0) = 1.0 since every number to the power is 1; on the other hand the pow() method returns double thus 1 becomes 1.0 Abdul Rahman Sherzad Page 2 of 11
  • 3. https://www.facebook. com/Oxus20 9) Which of the following is a valid identifier?  $343  class  9X  8+9  radius  _999  All variable names must begin with a letter of the alphabet, an underscore ( _ ), or a dollar sign ($).  You cannot use a java keyword (reserved word) for a variable name. 10) Which of the following is a constant, according to Java naming conventions?  MAX_VALUE  Test  read  ReadInt Use ALL_UPPER_CASE for your named constants,  COUNT  Variable_Name separating words with the underscore character. For example, use TAX_RATE rather than taxRate or TAXRATE. 11) Analyze the following code: Code 1: int number = 45; boolean even; if (number % 2 == 0) even = true; else even = false; Code 2: boolean even = (number % 2 == 0);  Code 1 has compile errors.  Code 2 has compile errors.  Both Code 1 and Code 2 have compile errors.  Both Code 1 and Code 2 are correct, but Code 2 is better. boolean even = (number % 2 == 0);  The above expression interprets as if the number is completely divisible by 2 even will be set to true else even will be set to false. Abdul Rahman Sherzad Page 3 of 11
  • 4. https://www.facebook. com/Oxus20 12) What is the exact output of the following code? double area = 3.5; System.out.print("area"); System.out.print(area);  3.53.5  3.5 3.5  area3.5  area 3.5 System.out.print("area"); // the word area will be printed as it appears between "" with cursor on same line. System.out.println(area); // the word area will be interpreted as 3.5 this time because it does not appear between "". 13) How many times will the following code print "Welcome to OXUS 20"? int count = 0; while (count++ < 10) { System.out.println("Welcome to OXUS 20"); } 8 9  10  11 The above code can be written as follow: int count = 0; while (count < 10) { System.out.println("Welcome to OXUS 20"); count++; }  The loop start from 0 (0 is inclusive) and continues until 10 (10 is not included)  Interval demonstration [0, 10) 14) What is the result of -7 % 5 is _____? 2 0  -2  -7 Abdul Rahman Sherzad JAVA language developers decided to choose the sign of the result equals the sign of the dividend in modulus expression. Thus, in expression -7 % 5 the dividend is -7, so result of modulus will be evaluated to -2. Page 4 of 11
  • 5. https://www.facebook. com/Oxus20 15) You should fill in the blank in the following code with ______________. public class Test { public static void main(String[] args) { System.out.print("The grade is "); printGrade(78.5); System.out.print("The grade is "); printGrade(59.5); } public static __________ printGrade(double score) { if (score >= 90.0) { System.out.println('A'); } else if (score >= 80.0) { System.out.println('B'); } else if (score >= 70.0) { System.out.println('C'); } else if (score >= 60.0) { System.out.println('D'); } else { System.out.println('F'); } } }  int  double  boolean  char  void  String  void is the correct answer because the printGrade() method does not return anything; it simply prints the result. 16) The following code fragment reads in two numbers: public static void main(String[] args) { Scanner input = new Scanner(System.in); int i = input.nextInt(); double d = input.nextDouble(); } What are the correct ways to enter these two numbers?  Enter an integer, a space, a double value, and then the Enter key.  Enter an integer, two spaces, a double value, and then the Enter key.  Enter an integer, an Enter key, a double value, and then the Enter key.  Enter a numeric value with a decimal point, a space, an integer, and then the Enter key. Abdul Rahman Sherzad Page 5 of 11
  • 6. https://www.facebook. com/Oxus20 PART II – Write output of the followings programs: 1. What output is produced by the following program? public class Test { public static void main(String[] args) { int limit = 100, num1 = 10, num2 = 20; if (limit <= limit) { if (num1 == num2) System.out.println("Tricky Question"); System.out.println("OXUS 20"); } System.out.println("OXUS means (Amu Darya)"); } } OXUS 20 OXUS means (Amu Darya) Following is the correct indentation and syntax of above program: public class Test { public static void main(String[] args) { int limit = 100, num1 = 10, num2 = 20; if (limit <= limit) { if (num1 == num2) { System.out.println("Tricky Question"); } System.out.println("OXUS 20"); } System.out.println("OXUS means (Amu Darya)"); } } 2. What output is produced by the following program? public class Test { public static void main(String[] args) { char c1 = 'A'; char c2 = 'B'; System.out.println(c1 + c2); } } 131 Why the output is 131? Because:   'B' = 66  Abdul Rahman Sherzad 'A' = 65 'A' + 'B' => 65 + 66 = 131 Page 6 of 11
  • 7. https://www.facebook. com/Oxus20 1. What output is produced by the following program? public class Test { public static void main(String[] args) { char c1 = 'A'; char c2 = 'B'; System.out.println("" + c1 + c2); } } Why the output is AB? Because java calculates the expression from AB left to right as follow:  "" + c1 = "A"  "A" + c2 = "AB" // String plus char will be converted to String  Thus output will be AB // String plus char will be converted to String 1. What output is produced by the following program? public class Test { public static void main(String[] args) { char c1 = 'A'; char c2 = 'B'; System.out.println(c1 + c2 + ""); } } Why the output is 131? Because java calculates the expression from 131 left to right as follow:  c1 + c2 => 'A' + 'B' => 65 + 66 = 131 // Both will be considered as interger  Now 131 + "" = "131" // integer plus String will be evaluated to String  Abdul Rahman Sherzad Thus output will be 131 Page 7 of 11
  • 8. https://www.facebook. com/Oxus20 PART III – Write the program for the following s: 1. Write a method called isAlphaNumeric that accepts a character parameter and returns true if that character is either an uppercase, lowercase or numeric letter. Method1: Using Regular Expression public static boolean isAlphanumeric(String input) { if (input == null || input.length() == 0) return false; if (input.matches("[a-zA-Z0-9]+")) { return true; } else { return false; } } Method2: Using for loop public static boolean isAlphanumeric(String input) { if (input == null || input.length() == 0) return false; for (int i = 0; i < input.length(); i++) { char c = input.charAt(i); if (!((c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') || (c >= '0' && c <= '9'))) { return false; } } return true; } Method3: Using for loop with Character Wrapper Class public static boolean isAlphanumeric(String input) { if (input == null || input.length() == 0) return false; for (int i = 0; i < input.length(); i++) { char c = input.charAt(i); if (!Character.isLetterOrDigit(c)) { return false; } } return true; } Abdul Rahman Sherzad Page 8 of 11
  • 9. https://www.facebook. com/Oxus20 2. Write a method to count the number of occurrences of a char in a String? Method1: Using loop with support of String methods public static int countOccurrences(String strInput, char needle) { int count = 0; for (int i = 0; i < strInput.length(); i++) { if (strInput.charAt(i) == needle) { count++; } } return count; } Method1: Using Advanced for loop public static int countOccurrences(String strInput, char needle) { int count = 0; for (char c : strInput.toCharArray()) { if (c == needle) { count++; } } return count; } Method1: Using String replaceAll() method public static int countOccurrences(String strInput, char needle) { return strInput.length() - strInput.replaceAll(String.valueOf(needle), "").length(); } return strInput.length() - strInput.replaceAll(String.valueOf(needle), "").length(); Consider strInput = "Abdul Rahman Sherzad" and needle = 'a' strInput.length() // 20 strInput.replaceAll(String.valueOf(needle), ""); // Abdul Rhmn Sherzd "Abdul Rhmn Sherzd".length() // 17 Return 20 – 17 = 3 // Thus, letter 'a' appears 3 times in "Abdul Rahman Sherzad". Abdul Rahman Sherzad Page 9 of 11
  • 10. https://www.facebook. com/Oxus20 3. Write a method called sumRange that accepts two integers as parameters that represent a range. Print an error message and return zero if the second parameter is less than the first. Otherwise, the method should return the sum of the integers in that range (both first and second parameters are inclusive). public static int sumRange(int start, int end) { int sum = 0; if (end < start) { System.err.println("ERROR: Invalid Rangen"); } else { for (int num = start; num <= end; num++) { sum = sum + num; } } return sum; } 4. Write a method called isAlpha that accepts a String as parameter and returns true if the given String contains only either uppercase or lowercase alphabetic letters. Method1: Using Regular Expression public static boolean isAlpha(String input) { if (input == null || input.length() == 0) return false; if (input.matches("[a-zA-Z]+")) return true; return false; } Method2: Using for loop public static boolean isAlpha(String input) { if (input == null || input.length() == 0) return false; for (int i = 0; i < input.length(); i++) { char c = input.charAt(i); if (!((c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z'))) { return false; } } return true; } Note: similar functionality is provided by the Character.isLetter(c) method as follow: if (!Character.isLetter(c)) { return false; } Abdul Rahman Sherzad OX US20 Page 10 of 11
  • 11. https://www.facebook. com/Oxus20 Society is the premier Computer society Science professionals and founded of IT in March 2013. The society's goal is to provide information and assistance to Computer Science professionals, increase their job performance and overall agency function by providing cost effective products, services and educational opportunities. So the society believes with the education of Computer Science and IT they can help their nation to higher standards of living. Follow us on Facebook, https://www.facebook.com/Oxus20 Abdul Rahman Sherzad Page 11 of 11