Interview Questions and Answers for 'Java' | Search Interview Question

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Q1541. What doesn Http keep alive header does ?

Ans. Http is connection less by default. header informs hosts to keep the connection alive so that the same connection can be reused for multiple communication.

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Q1542. 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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Q1543. 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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Q1544. 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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Q1545. How many elements will be there in TreeSet after the last line and Why ?

TreeSet set = new TreeSet();
set .add(new String("abc"));
set .add(new String("abc"));

Core Java

Ans. One.

As we haven't specified the type of TreeSet, it being evaluated with the first element insertion. Once it's identified that it's of type String and as no comparator has been defined, the comparison is done using the String compareTo method. String compareTo method compares the elements by the content / value.

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Q1546. 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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Q1547. 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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Q1548. Difference between HashMap and WeakHashMap ?

Ans. WeakHashMap uses weak reference for keys, which means if the key object doesn't have any reference then both key/value mapping will become eligible for garbage collection.

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Q1549. Difference between Stack and Heap memory ?

Core Java

Ans. Stack memory areas is used to hold method and local variables while objects are always allocated memory in the heap. The heap memory is shared between multiple threads whereas Stack memory isn't.

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Q1550. Which tree is used to implement TreeMap in Java?

Ans. Red Black Tree

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Q1551. What is collision in hash collections ?

Core Java

Ans. Collision is the situation when two different elements have the same Hash Code.

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Q1552. When are static and instance methods resolved ? During compile time or Runtime ?

Ans. Static methods are resolved during compile time and hence they cannot participate in runtime polymorphism. Instance methods are resolved during runtime.

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Q1553. What will be the output ?Integer a = 10, b =10;Integer c = 10, d = 1000;System.out.println(a == b);System.out.println(c ==d);

Core Java

Ans. truefalse

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Q1554. How to determine if the linked list has a cycle in it ?

Ans. http://stackoverflow.com/questions/494830/how-to-determine-if-a-linked-list-has-a-cycle-using-only-two-memory-locations

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Q1555. Can we have multiple classes in single file ?

Ans. Yes, but there can be only 1 public class in a single file.

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Q1556. What is a BlockingQueue?

Data Structures

Ans. BlockingQueue is a Queue that supports operations that wait for the queue to become non-empty when retrieving and removing an element, and wait for space to become available in the queue when adding an element.

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Q1557. What is OutOfMemoryError in Java?

Core Java

Ans. OutOfMemoryError in Java is a subclass of VirtualMachineError and is thrown by JVM when it runs out of heap memory.

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Q1558. Do you know of any facility to convert between Scala and Java Util Collections ?

Scala

Ans. We can use JavaConversions which is a part of Scala Library.

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Q1559. Have you used Kafka in your project ? If Yes, for what ?

Ans. We were using Kafka as a replacement for JMS Message Queue for better throughput. We were just using a simple Java multi threaded client as order of message consumption didn't matter to us.

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Q1560. Which interfaces are implemented by BatchUpdateException?

Ans. [Iterable]

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Q1561. What is the package name for CertStoreParameters class?

Ans. java.lang

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Q1562. Which is the Parent Class of CertStoreParameters class?

Ans. Clonable

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Q1563. Which access specifiers can be used with top level class ? a. public or default b. public or private c. public or protected d. protected or default

Core Java

Ans. public or default

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Q1564. Which of the following can be marked static ?

a. Methods , Variables and Initialization Blocks.
b. Methods , Variables , Initialization Blocks and Outer Classes and nested Classes.
c. Methods , Variables , Initialization Blocks and Outer Classes.
d. Methods , Variables , Initialization Blocks and nested Classes

Core Java

Ans. Methods , Variables , Initialization Blocks and nested Classes

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Q1565. Which of the following cannot be marked static ?

a. Constructors , Classes ( Outer ) , Classes ( nested ), Interfaces , Local variables , Inner Class methods and instance variables.
b. Constructors , Classes ( Outer ) , Interfaces , Local variables , Class variables , Class Methods , Inner Class methods and instance variables.
c. Constructors , Classes ( Outer ) , Interfaces , Local variables , Inner Class methods and instance variables.
d. Constructors , Classes ( Outer ) , Classes (Nested), Interfaces , Local variables , Inner Class methods and instance variables

Ans. Constructors , Classes ( Outer ) , Interfaces , Local variables , Inner Class methods and instance variables.

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Q1566. Which is of the following is NOT TRUE for JVM ?

a. JVM reads Byte Code and generates Machine Code.
b. JVM is a virtual Machine that acts as a intermediary between Java Application and Host Operating System.
c. JVM reads Source Code and generates Byte Code.
d. JVM acts as a translator that translates different Machine code ( on the basis of Host Machine ) for a common Byte Code.

Ans. JVM reads Source Code and generates Byte Code.

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Q1567. Interface can only have ...

a. Member elements and Methods.
b. Static Variables and Static Methods.
c. Static Final Variables and Instance Method Declarations.
d. Member Elements , Instance Methods, Static variables and Static Methods.

Ans. Static Final Variables and Instance Method Declarations.

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Q1568. Which of the following collection maintain its elements in Natural Sorted order ?

a. HashMap
b. TreeMap
c. LinkedHashMap
d. LinkedMap

Ans. TreeMap

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Q1569. Which of the following collections stores its elements in insertion Order ?

a. HashMap
b. TreeMap
c. LinkedHashMap
d. LinkedMap

Core Java

Ans. LinkedHashMap

Sample Code for LinkedHashMap

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Q1570. If we add Enum constants to a sorted collection ( Treemap , TreeSet ), What will be the order in which they will be maintained ?

a. Sorted Collection wont maintain them in any order.
b. Insertion Order
c. Order in which constants are declared.
d. Natural Sorting Order.

Ans. Order in which constants are declared.

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