JAVA Programming Questions and Answers PART III

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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. M e t ho d I: - Us in g L o op 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 2 nd 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 M e t ho d I I :- Us in g R e g u la r E xp r es s ion 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 5
  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. M e t ho d I: - Us in g Lo op 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 M e t ho d I I :- Us in g r e ve rs e ( ) m e t ho d o f S t ri n g B u i ld e r / S t r in g Bu f f e r c la s s 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. M e t ho d I I I:- Us in g s ubs t r in g ( ) a n d Re c u rs i o n 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 5
  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. M e t ho d I: - Us in g R a nd om c la s s o f ja va .u t il p a c ka g e 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. M e t ho d I I :- Us in g M a t h .r a nd om ( ) m e th o d 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 5
  4. 4. https://www.facebook. com/Oxus20 PART II – Single Choice and Multiple Choices: 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 w ith 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 5
  5. 5. https://www.facebook. com/Oxus20 4. A constructor  A. mus t have the same name as the class it is declared w ithin.  B. is used to create objects.  C. may be declared private  D. A ll the above  A. A c o n s t r u c t o r m u s t h a ve 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 e c l a r e d w i t h i n . public class OXUS20 { public OXUS20() { } }  B. C o n s t ru c t o r i s u s e d t o c re a te o b j e c ts OXUS20 amu_darya = new OXUS20();  C. C o n s t ru c t o r m a y b e d e c l a r e d p r i va 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 5
  6. 6. ‫‪OXUS20 is a non-profit society with the aim of changing education for the better‬‬ ‫.‪by providing education and assistance to IT and computer science professionals‬‬ ‫آکسیوس20 یک انجمن غیر انتفاعی با هدف تغییرو تقویت آموزش و پرورش از طریق ارائه آموزش و کمک به متخصصان علوم‬ ‫کامپیوتر است.‬ ‫نام این انجمن برگرفته از دریای آمو پر آب ترین رود آسیای میانه که دست موج آن بیانگر استعداد های نهفته این انجمن بوده، و این دریا از دامنه های کهن پامیر‬ ‫سرچشمه گرفته و ماورای شمالی سرزمین باستانی افغانستان را آبیاری میکند که این حالت دریا هدف ارایه خدمات انجمن را انعکاس میدهد.‬ ‫آکسیوس20 در نظر دارد تا خدماتی مانند ایجاد فضای مناسب برای تجلی استعدادها و برانگیختن خالقیت و شکوفایی علمی محصالن و دانش پژوهان، نهادمند‬ ‫ساختن فعالیت های فوق برنامه علمی و کاربردی، شناسایی افراد خالق، نخبه و عالقمند و بهره گیری از مشارکت آنها در ارتقای فضای علمی پوهنتون ها و دیگر‬ ‫مراکز آموزشی و جامعه همچون تولید و انتشار نشریات علمی تخصصی علوم عصری و تکنالوژی معلوماتی را به شکل موثر آن در جامعه در راستای هرچه بهتر‬ ‫شدن زمینه تدریس، تحقیق و پژوهش و راه های رسیدن به آمال افراد جامعه را فراهم میسازد.‬ ‫,‪Follow us on Facebook‬‬ ‫02‪https://www.facebook.com/Oxus‬‬

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