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Core Java - Interview Questions and Answers for 'Data type' - 39 question(s) found - Order By Newest

Q1. What is casting?

^Anonymous

Ans. There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference

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Q2. What are the Wrapper classes available for primitive types ?

^Anonymous

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

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Q3. What are wrapper classes ?

^Anonymous

Ans. They are wrappers to primitive data types. They allow us to access primitives as objects.

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Q4. What is Generalization and Specialization in terms of casting ?

^{Admin
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Ans. Generalization or UpCasting is a phenomenon where a sub class is prompted to a super class, and hence becomes more general. Generalization needs widening or up-casting. Specialization or DownCasting is a phenomenon where a super class is narrowed down to a sub class. Specialization needs narrowing or down-casting.

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Q5. Why Java is not considered pure OOP's language ?

Ans. There are 2 reasons for it.

1. Usage of Primitive types - Though Java provides classes for the primitive data types but as the usage of primitives is permissible, its considered unpure OOP's language.

2. Usage of Static members - Static members belong to the class and not objects and hence not considered fit for pure OOP's programming.

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Q6. What are the default or implicitly assigned values for data types in java ?

^Anonymous

Ans. boolean ---> false
byte ----> 0
short ----> 0
int -----> 0
long ------> 0l
char -----> /u0000
float ------> 0.0f
double ----> 0.0d
any object reference ----> null

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Q7. What is the difference between float and double?

^{Admin
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Ans. Float can represent up to 7 digits accurately after decimal point, where as double can represent up to 15 digits accurately after decimal point.

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Q8. How do you prefer to store money values in your application ?

^{2016-11-15 09:38:25}

Ans. At Application level we use either Double or BigDecimal , preferably BigDecimal. At Database level we use Number with decimal precision 3.

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Q9. Difference between long.Class and Long.TYPE ?

^Anonymous

Ans. They both represent the long primitive type. They are exactly the same.

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Q10. What data type Variable can be used in a switch statement ?

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Ans. Variables used in a switch statement can only be a byte, short, int, or char ( and String with Java 7 and above )

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Q11. Variable of the boolean type is automatically initialized as?

^{Admin
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Ans. The default value of the boolean type is false.

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Q12. Name few classes that extends Number Class ?

^{Admin
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Ans. http://www.buggybread.com/2015/02/java-util-classes-that-inherit-number.html

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Q13. Name few Boolean classes and interfaces ?

^{Admin
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Ans. http://www.buggybread.com/2015/01/java-data-types-double-classes-and_31.html

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Q14. Name few Double data types related classes and interfaces ?

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

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Q15. Name few float data type related classes and interfaces ?

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

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Q16. Name few Integer related classes and interfaces ?

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

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Q17. Name few long data type related classes and interfaces ?

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

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Q18. What is the difference between Data Type and Data Structure ?

^{Admin
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Ans. Data type: a set of values together with operations on that type
Data structure: a physical implementation of a data type

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Q19. Is it correct to say that Interfaces are abstract data types ?

^{Admin
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Ans. No.

Data Type holds data whereas Interface doesn't hold anything. Interface is a contract about how to communicate with the underlying Class.

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Q20. Do you see Class as a Data Type or Data Structure ?

^{Admin
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Ans. Class can be better seen as Data Type. This could be implemented as a Data Structure too in some cases.

One thing worth understanding here is that Data type and Data structure are conceptual things. Class could be implementation of either of these.

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Q21. Which of the following data type you will prefer to store price - BigDecimal or Double ?

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Ans. BigDecimal if memory and Performance is not critical concern, otherwise double.

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Q22. Which takes more memory - float or Float ?

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Ans. float is a native data type whereas Float is a class. A Float object will always take more memory than float variable as there are metadata overheads with the objects.

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Q23. What is the size of long data type ?

a. 16 bit
b. 32 bit
c. 64 bit
d. 128 bit

^Anonymous

Ans. 64 bit

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Q24. What is the size of double type ?

a. 16 bit
b. 32 bit
c. 64 bit
d. 128 bit

^Anonymous

Ans. 64 bit

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Q25. What is the size of short type ?

a. 8 bit
b. 16 bit
c. 32 bit
d. 128 bit

^Anonymous

Ans. 16 bit

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Q26. What is ADT or Abtstract Data Type ?

Ans. ADT is a container which holds different types of objects with specifications.

For example - Stack, Array, Liked list, Tree

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Q27. Why calculations in float or Double sometimes gives unpredictable results ?

^{2016-11-21 11:26:07}

Ans. Because the way float values are stored its not precise.

For example - 0.1 is actually stored as
0.1000000000000000055511151231257827021181583404541015625

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Q28. How does Java handle integer overflows and underflows?

^{2017-01-12 11:18:41}

Ans. It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.

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Q29. What are the different primitive data types in Java ?

^{2017-01-28 15:14:23}

Ans. boolean
byte
char
double
float
int
long
short
void

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Q30. Difference between int and short data types ?

^{2017-03-24 09:15:23}

Ans. Both holds numeric values. short is a 16-bit signed two's complement integer whereas int is a 32-bit signed two's complement integer.

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Q31. What is widening and narrowing conversion in Java ?

^{2017-06-06 12:30:31}

Ans. Conversion means that the expression / literal / value of one type getting converted to other type.

Widening conversion is the conversion from Type A to Type B where B requires a wider space than A. For example - int to long, float to double, char to String etc. As the value moves to a wider space, there is no loss of information.

Narrowing conversion is the conversion from Type A to Type B where B requires a narrower space space than A. For example - int to long, float to double, char to String etc.As the value moves to a narrower space, there is a loss of information.

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Q32. What is Boxing conversion ?

^{2017-06-06 12:31:36}

Ans. Boxing conversion converts expressions of primitive type to corresponding expressions of reference type.

For example

boolean to Boolean
long to Long
double to Double

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Q33. Is String a Data type in Java ?

^{2017-06-18 18:04:10}

Ans. String is not a primitive type in java. Anything defined within double quotes like "abc" is an object of String class.

Sample Code for String

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Q34. Are char,String and Char data types in java ?

^{2017-06-18 18:05:30}

Ans. char is a primitive data type. String is a class. Char is a wrapper class for primitive char.

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Q35. What will be the output of following code and Why ?

int x = 5;
int y = 7;
float f = 5f;
float z = y / x * f;
System.out.println(z);

^{2017-07-23 20:00:12}

Ans. 5.0

operation between two ints generate int only. so 7/5 generates 1 and not 1.4. Multiplication between int and float generates float and hence

1 * 5.0 = 5.0

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Q36. What do we mean by a Data Type ?

^{2017-08-08 15:15:15}

Ans. if you have similar type of data or objects or entities, then we can give them a type with unique name. And this name will be our Data type.

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Q37. In the Following code which foo will get called.

foo(Integer i){
}

foo(String s){
}

public static void main(){
passing foo(null);
}

^{2018-01-21 17:16:39}

Ans. ambiguity error

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Q38. What is the advantage of BidDecimal over Double ?

^{2018-04-10 15:04:39}

^{This question is still unanswered. Can you please provide an answer.}

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Q39. What will be the output of following ?

public class BuggyBread {

   private int x;
   private Integer y;

   BuggyBread(int x,int y){};

   public static void main(String[] args){
      BuggyBread buggybread = new BuggyBread(1,2);
      System.out.println(buggybread.x);
      System.out.println(buggybread.y);
   }
}    Reference

a. 0 0

b. 0 null

c. null 0

d. null null

Ans.b. 0 null