Oxus20 is a non-profit organization aimed at improving education by providing training and assistance to IT and computer science professionals. The name Oxus20 comes from the Amu Darya river, the largest river in Central Asia, which represents the hidden talents that the organization aims to develop. The organization seeks to create an environment conducive to nurturing talent and creativity among students and researchers, institutionalize extra-curricular scientific activities, identify gifted individuals to involve in advancing the scientific community, and produce specialized publications to disseminate modern science and technology in society.

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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
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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
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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

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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
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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. ‫‪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.‬
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