JAVA Programming Questions and Answers PART III

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. 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
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
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)


Page 2 of 5


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;









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().


Page 3 of 5


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 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


 C. 20

 E. river

Page 4 of 5


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 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

}


Page 5 of 5

‫‪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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JAVA Programming Questions and Answers PART III

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