Java - Interview Questions and Answers on Integers

Q1.  What are the Wrapper classes available for primitive types ?

Ans. boolean  - java.lang.Boolean
byte - java.lang.Byte
char - java.lang.Character
double - java.lang.Double
float - java.lang.Float
int - java.lang.Integer
long - java.lang.Long
short - java.lang.Short
void - java.lang.Void

Q2.  Will this code give error if i try to add two heterogeneous elements in the arraylist. ? and Why ?

List list1 = new ArrayList<>();
list1.add(5);
list1.add("5");

Ans. If we don't declare the list to be of specific type, it treats it as list of objects.

int 1 is auto boxed to Integer and "1" is String and hence both are objects.

Q3.  How to find whether a given integer is odd or even without use of modules operator in java?

Ans. public static void main(String ar[])
{
     int n=5;
     if((n/2)*2==n)
     {
          System.out.println("Even Number ");
     }
     else
     {
          System.out.println("Odd Number ");
     }
}
}

Q4.  Is it legal to initialize List like this ?

LinkedList<Integer> l=new LinkedList<int>(); 

Ans. No, Generic parameters cannot be primitives.

Q5.  What will the following code print ?

public static void main(String[] args){
Integer i1 = new Integer("1");
        Integer i2 = new Integer("2");
        Integer i3 = Integer.valueOf("3"); 
        int i4 = i1 + i2 + i3; 
        System.out.println(i4);  
}

Ans. 6

Q6.  Which of the following syntax are correct ?

a. LinkedList<Integer> l=new LinkedList<int>();
b. List<Integer> l=new LinkedList<int>();
c. LinkedList<Integer> l=new LinkedList<Integer>();
d. List<Integer> l = new LinkedList<Integer>();

Ans. c and d are correct.

Q7.  Can we compare Integers by using equals() in Java ?

Ans. Yes for the Wrapper class Integer but not for the primitive int.

Q8.  Name few Integer related classes and interfaces ?

Ans. http://www.buggybread.com/2015/01/java-data-types-integer-classes-and.html

Q9. Which is the Parent Class of  Integer class?

Ans.Number

Q10. Which interfaces are implemented by  Integer?

Ans.[Comparable]

Q11. What is the package name for Integer class?

Ans.java.lang

Q12.  If you have access to a function that returns a random integer from one to five, write another function which returns a random integer from one to seven.

Ans. We can do that by pulling binary representation using 3 bits ( random(2) ).

getRandom7()  {
      String binaryStr = String.valuesOf(random(2))+String.valuesOf(random(2))+String.valuesOf(random(2));
      binaryInt = Integer.valueOf(binaryStr); 
      int sumValue=0;
      int multiple = 1;
      while(binaryInt > 0){
             binaryDigit = binaryInt%10;
             binaryInt = binaryInt /10;
             sumValue = sumValue + (binaryDigit * multiple);
             multiple = multiple * 2;
      }
}             

Q13.  Write a method to convert binary to a number ?

Ans. convert(int binaryInt)  {
     int sumValue=0;
      int multiple = 1;
      while(binaryInt > 0){
             binaryDigit = binaryInt%10;
             binaryInt = binaryInt /10;
             sumValue = sumValue + (binaryDigit * multiple);
             multiple = multiple * 2;
      }
      return sumValue;
}         

Q14.  How to find whether a given integer is odd or even without use of modules operator in java?

Ans. public static void main(String ar[])
{
     int n=5;
     if((n/2)*2==n)
     {
          System.out.println("Even Number ");
     }
     else
     {
          System.out.println("Odd Number ");
     }
}
}

Q15.  What will be the output of following code ?

public static void main(String[] args) 
{ 
     int x = 10; 
     int y; 
     if (x < 100) y = x / 0; 
     if (x >= 100) y = x * 0; 
     System.out.println("The value of y is: " + y); 
}

Ans. The code will not compile raising an error that the local variable y might not have been initialized. Unlike member variables, local variables are not automatically initialized to the default values for their declared type. 


Q16.  What will the following code print ?

public static void main(String[] args){
Integer i1 = new Integer("1");
        Integer i2 = new Integer("2");
        Integer i3 = Integer.valueOf("3"); 
        int i4 = i1 + i2 + i3; 
        System.out.println(i4);  
}

Ans. 6