OXUS20 JAVA Programming Questions and Answers PART III

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OXUS 20 is pleased to offer PART III 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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OXUS20 JAVA Programming Questions and Answers PART III

  1. 1. https://www.facebook. com/Oxus20 PART I – Scenario to program and code : 1. Write a method that accept a String named "strInput" as a parameter and returns every other character of that String parameter starting with the first character. Method I:- Using Loop public static String everyOther(String strInput) { String output = ""; for (int index = 0; index < strInput.length(); index += 2) { output += strInput.charAt(index); } return output; } Tips:  Each and every characters of the given String parameter needs to be scanned and processed. Therefore, we need to know the number of characters in the String. strInput.length(); st 1 character is needed that is why int index = 0; we don't need the 2nd character that is why we incremented index by 2 as follow: index += 2  strInput.charAt(index); reading the actual character and concatenated to the output variable.  Finally System.out.println( everyOther("SshHeErRzZaAdD") ); // will print Sherzad Method II:- Using Regular Expression public static String everyOther(String strInput) { return strInput.replaceAll("(.)(.)", "$1"); } Tips:  In Regular Expression . matches any character  In Regular Expression () use for grouping  strInput.replaceAll("(.)(.)", "$1"); // in the expression (.)(.), there are two groups and each group matches any character; then, in the replacement string, we can refer to the text of group 1 with the expression $1. Therefore, every other character will be returned as follow: System.out.println( everyOther("SshHeErRzZaAdD") ); // will print Sherzad Abdul Rahman Sherzad Page 1 of 6
  2. 2. https://www.facebook. com/Oxus20 2. Write a method named reverseString that accepts a String parameter and returns the reverse of the given String parameter. Method I:- Using Loop public static String reverseString(String strInput) { String output = ""; for (int index = (strInput.length() - 1); index >= 0; index--) { output += strInput.charAt(index); } return output; } Tips:  Each and every characters of the given String parameter needs to be scanned and processed. Therefore, we need to know the number of characters in the String. strInput.length();  Since index ranges from 0 to strInput.length() - 1; that is why we read each and every character from the end int index = (strInput.length() - 1);  Finally System.out.println( reverseString("02SUXO") ); // will print OXUS20 Method II:- Using reverse() method of StringBuilder / StringBuffer class public static String reverseString(String strInput) { if ((strInput == null) || (strInput.length() <= 1)) { return strInput; } return new StringBuffer(strInput).reverse().toString(); } Tips:  Both StringBuilder and StringBuffer class have a reverse method. They work pretty much the same, except that methods in StringBuilder are not synchronized. Method III:- Using substring() and Recursion public static String reverseString(String strInput) { if ( strInput.equals("") ) return ""; return reverseString(strInput.substring(1)) + strInput.substring(0, 1); } public String substring(int beginIndex) public String substring(int beginIndex, int endIndex) Abdul Rahman Sherzad Page 2 of 6
  3. 3. https://www.facebook. com/Oxus20 3. Write a method to generate a random number in a specific range. For instance, if the given range is 15 - 25, meaning that 15 is the smallest possible value the random number can take, and 25 is the biggest. Any other number in between these numbers is possible to be a value, too. Method I:- Using Random class of java.util package public static int rangeInt(int min, int max) { java.util.Random rand = new java.util.Random(); int randomOutput = rand.nextInt((max - min) + 1) + min; return randomOutput; } Tips:  The nextInt(int n) method is used to get an int value between 0 (inclusive) and the specified value (exclusive).  Consider min = 15, max = 25, then o rand.nextInt(max - min) // return a random int between 0 (inclusive) and 10 (exclusive). Interval demonstration [0, 10) o rand.nextInt((max - min) + 1) // return a random int 0 and 10 both inclusive o rand.nextInt((max - min) + 1) + min // return a random int 0 and 10 both inclusive + 15;  if the return random int is 0 then 0 + 15 will be 15;  if the return random int is 10 then 10 + 15 will be 25;  if the return random int is 5 then 5 + 15 will be 20;  Hence the return random int will be between min and max value both inclusive. Method II:- Using Math.random() method public static int rangeInt(int min, int max) { return (int) ( Math.random() * ( (max – min) + 1 ) ) + min; } Note:  In practice, the Random class is often preferable to Math.random(). Abdul Rahman Sherzad Page 3 of 6
  4. 4. https://www.facebook. com/Oxus20 PART II – Single Choice and Multiple Choice s: 1. Which of the following declarations is correct?  [A] boolean b = TRUE;  [B] byte b = 255; [A] boolean b = TRUE; // JAVA is Case Sensitive!  [C] String s = "null"; [B] byte b = 255; // Out of range MIN_VALUE = -128 and MAX_VALUE = 127  [D] int i = new Integer("56"); [C] String s = "null"; // Everything between double quotes "" considered as String [D] int i = new Integer("56"); // The string "56" is converted to an int value. 2. Consider the following program: import oxus20Library.*; public class OXUS20 { public static void main(String[] args) { // The code goes here ... } } What is the name of the java file containing this program?  A. oxus20Library.java  B. OXUS20.java  Each JAVA source file can contain only one public class.  C. OXUS20  The source file's name has to be the name of that public class. By convention, the  D. OXUS20.class source file uses a .java filename extension  E. Any file name with the java suffix is accepted 3. Consider the following code snippet public class OXUS20 { public static void main(String[] args) { String river = new String("OXUS means Amu Darya"); System.out.println(river.length()); } } What is printed?  A. 17  B. OXUS means Amu Darya Abdul Rahman Sherzad  C. 20  E. river Page 4 of 6
  5. 5. https://www.facebook. com/Oxus20 4. A constructor  A. must have the same name as the class it is declared within.  B. is used to create objects.  C. may be declared private  D. All the above  A. A c o n s t r u c t o r m u s t h a v e t h e s a m e n a m e a s t h e c l a s s i t i s d ec l a r ed w i t h i n . public class OXUS20 { public OXUS20() { } }  B. C o n s t r u c t o r i s u s ed t o c r e a t e o b j e c t s OXUS20 amu_darya = new OXUS20();  C. C o n s t r u c t o r m a y b e d e c l a r ed p r i v a t e // private constructor is off course to restrict instantiation of the class. Actually a good use of private constructor is in Singleton Pattern. 5. Which of the following may be part of a class definition?  A. instance variables  B. instance methods Following is a sample of class declaration:  C. constructors  D. All of the above class MyClass {  Field // class variables or instance variables  E. None of the above  constructor, and // class constructor or overloaded constructors  method declarations // class methods or instance methods } Abdul Rahman Sherzad Page 5 of 6
  6. 6. https://www.facebook. com/Oxus20 is a nonprofit society with the aim of changing education for the better by providing education and assistance to Computer Science and IT professionals. 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 6 of 6

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