1. Which of these is a super class of wrappers Double and Float?
a) Long
b) Digits
c) Float
d) Number
Explanation: Number is an abstract class containing subclasses Double, Float, Byte, Short, Integer and Long.
2. Which of the following methods return the value as a double?
a) doubleValue()
b) converDouble()
c) getDouble()
d) getDoubleValue()
Explanation: doubleValue()
3. Which of these methods can be used to check whether the given value is a number or not?
a) isNaN()
b) isNumber()
c) checkNaN()
d) checkNumber()
Explanation: isNaN() methods returns true if num specified is not a number, otherwise it returns false.
4. Which of these method of Double wrapper can be used to check whether a given value is infinite or not?
a) Infinite()
b) isInfinite()
c) checkInfinite()
d) None of the mentioned
Explanation: isInfinite() methods returns true if the specified value is an infinite value otherwise it returns false.
5. Which of these exceptions is thrown by compareTo() method defined in a double wrapper?
a) IOException
b) SystemException
c) CastException
d) ClassCastException
Explanation: compareTo() methods compare the specified object to be double, if it is not then ClassCastException is thrown.
6. What will be the output of the following Java code?
class Output
{
public static void main(String args[])
{
Double i = new Double(257.5);
boolean x = i.isNaN();
System.out.print(x);
}
}
a) true
b) false
c) 0
d) 1
Explanation: i.isNaN() method returns returns true if i is not a number and false when i is a number. Here false is returned because i is a number i:e 257.5.
Output:
false
7. What will be the output of the following Java code?
class Output
{
public static void main(String args[])
{
Double i = new Double(257.578);
int x = i.intValue();
System.out.print(x);
}
}
a) 0
b) 1
c) 256
d) 257
Explanation: i.intValue() method returns the value of wrapper i as a Integer. i is 257.578 is double number when converted to an integer data type its value is 257.
Output:
257
8. What will be the output of the following Java code?
class Output
{
public static void main(String args[])
{
Double i = new Double(257.578123456789);
float x = i.floatValue();
System.out.print(x);
}
}
a) 0
b) 257.0
c) 257.57812
d) 257.578123456789
Explanation: floatValue() converts the value of wrapper i into float, since float can measure till 5 places after decimal hence 257.57812 is stored in floating point variable x.
Output:
257.57812
9. What will be the output of the following Java code?
class Output
{
public static void main(String args[])
{
Double y = new Double(257.57812);
Double i = new Double(257.578123456789);
try
{
int x = i.compareTo(y);
System.out.print(x);
}
catch(ClassCastException e)
{
System.out.print("Exception");
}
}
}
a) 0
b) 1
c) Exception
d) None of the mentioned
Explanation: i.compareTo() methods two double values, if they are equal then 0 is returned and if not equal then 1 is returned, here 257.57812 and 257.578123456789 are not equal hence 1 is returned and stored in x.
Output:
1
10. Which of these packages contain classes and interfaces used for input & output operations of a program?
a) java.util
b) java.lang
c) java.io
d) all of the mentioned
Explanation: java.io provides support for input and output operations.