Core Java - Interview Questions and Answers for 'Data type' | Search Interview Question

Core Java - Interview Questions and Answers for 'Data type' - 38 question(s) found - Order By Newest

Q1. What is casting?

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 ?

Core Java

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 ?

Core Java

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

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Q4. Why Java is not considered pure OOP's language ?

Core Java

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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Q5. What is Generalization and Specialization in terms of casting ?

Core Java

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

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?

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 ?

Core Java

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 ?

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 ?

Core Java

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?

Core Java

Ans. The default value of the boolean type is false.

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Q12. Name few classes that extends Number Class ?

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 ?

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 ?

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 ?

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 ?

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 ?

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 ?

Core Java

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 ?

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 ?

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 ?

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

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Q22. Which takes more memory - float or Float ?

Core Java

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

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

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

Ans. 16 bit

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Q26. What is ADT or Abtstract Data Type ?

Core Java

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 ?

Core Java

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?

Core Java

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 ?

Core Java

Ans. boolean
byte
char
double
float
int
long
short
void

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Q30. Difference between int and short data types ?

Core Java

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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