Core Java - Interview Questions and Answers for 'Wrapper classe' | Search Interview Question

Core Java - Interview Questions and Answers for 'Wrapper classe' - 13 question(s) found - Order By Newest

Q1. 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.

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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. What are the benefits of using Wrapper classes over primitive types ?

Core Java

Ans. With Collection classes , we cannot use primitive types. Moreover for any class using generic types, we cannot use primitive types.

They add more functionality by means of additional methods.

As their reference can be null , they offer consistent check for uninitialized state.

They facilitate caching and reuse by means of constant Pools.

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Q5. Explain Autoboxing ?

Core Java

Ans. Autoboxing is the automatic conversion that the Java compiler makes between the primitive types and their corresponding object wrapper classes

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Q6. Difference between boolean and Boolean ?

Core Java

Ans. boolean is a primitive type whereas Boolean is a class.

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Q7. What are Wrapper Classes ? What are Primitive Wrapper Classes ?

Core Java

Ans. A wrapper class is any class which "wraps" or "encapsulates" the functionality of another class or component. A Wrapper Class that wraps or encapsulates the primitive data type is called Primitive Wrapper Class.

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Q8. What Design pattern Wrapper Classes implement ?

Design

Ans. Adapter.

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Q9. Can we compare Integers by using equals() in Java ?

Core Java

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

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Q10. Is this valid in Java ?

Long x = new Long ("42");

Core Java

Ans. Yes. Long wrapper class has overloaded constructor which takes String as input and then translate it to the long value and stored it as long.

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Q11. What is Boxing conversion ?

Core Java

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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Q12. Does Wrapper classes produces immutable objects ?

Core Java

Ans. Yes

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Q13. Is immutability an advantage with Wrapper classes over primitive types ?

Core Java

Ans. There is no concept of de referencing with primitive types and hence they are implicitly immutable. Having wrapper classes as mutable offers disadvantages compared to primitive types. Wrapper classes being immutable offer similar advantage as primitive types.It actually overshadows the disadvantage wrapper class could have if they are immutable.

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