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

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Not frequently asked as it was introduced with Java 8.

Q1451. What is StringJoiner ?

Ans. StringJoiner is a util method to construct a string with desired delimiter. This has been introduced with wef from Java 8.

Sample Code

StringJoiner strJoiner = new StringJoiner(".");

strJoiner.add("Buggy").add("Bread");

System.out.println(strJoiner); // prints Buggy.Bread

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Not frequently asked as it was introduced with Java 8.

Q1452. What is the use of Optional ?

Core Java

Ans. Optional is a good way to protect application from runtime nullPointerException in case the the absent value has been represented as null. So basically Optional class provides the type checking during compile time and hence will never result in NPE.

For ex -

List> intList = new ArrayList>();
intList.add(Optional.empty());
intList.add(Optional.of(new Employee("abc")));
intList.add(Optional.of(new Employee("xyz")));
intList.add(Optional.of(new Employee("123")));
System.out.println(intList.get(0).getName());

So Now , even when the first list element is empty, this code will never throw an NullPointerException.

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Q1453. Have you ever used StringTokenizer ?

Core Java

Ans. No, Alternatively I have used String.split("\\s") for achieving the same function.

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Q1454. What is ConcurrentLinkedDeque ?

Core Java

Ans. It's a Collections concrete class that provides implementation of a Double Ended queue that allows concurrent insertion, removal, and access operations that can be executed safely across multiple threads.

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Q1455. What is CopyOnWriteArrayList ?

Ans. Its a type of ArrayList in which all Write operations , i.e add and set are performed by creating a new copy. This array never changes during the lifetime of the iterator, so it never throws ConcurrentModificationException

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Q1456. What are the advantages and disadvantages of CopyOnWriteArrayList ?

Core Java

Ans. This collections class has been implemented in such a manner that it can never throw ConcurrentModificationException. As it performs update and write operations by creating a new copy of ArrayList, It's slower compared to ArrayList.

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Q1457. Name few Concurrent Collection Classes ?

Ans. ConcurrentHashMap
ConcurrentLinkedDeque
ConcurrentLinkedQueue
ConcurrentMap
ConcurrentNavigableMap
ConcurrentSkipListMap
ConcurrentSkipListSet

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Q1458. Name few Collections Map implementations ?

Ans. AbstractMap
ConcurrentHashMap
ConcurrentSkipListMap
EnumMap
HashMap
IdentityHashMap
LinkedHashMap
SystemFlavorMap
TreeMap
WeakHashMap

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Q1459. What is ConcurrentModificationException ?

Core Java

Ans. This is the exception that is thrown when we try to modify the non concurrent collection class while iterating through it.

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Q1460. What is ArrayIndexOutOfBoundException ?

Core Java

Ans. Exception thrown by the application is we try to access an element using an index which is not within the range of array i.e lower than 0 or greater than the size of the array.

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Q1461. how can we generate JavaDoc documentation for our code ?

Eclipse

Ans. In Eclipse, Go to File -> Export -> Java -> JavaDoc

Select the projects , other properties and output directory for which JavaDoc and Click Finish.

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Q1462. Can we generate Java Documentation using Export -> JavaDoc using a jar file ?

Eclipse

Ans. Yes, If the jar contains the source code. No, If it contains only classes.

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Q1463. Can we initialize member variables within static block ?

Ans. Static block is like static method that gets executed upon class loading. The way static method allows accessing member variables ( using object references only ), the same static block can also access and initialize member variables.

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Q1464. Difference between jar , war and ear ?

Java EE

Ans. Jar is Java Archieve i.e compressed Class or Class / Java files.

War comprises of compressed Servlet class files,JSP FIles,supporting files, GIF and HTML files.

Ear comprise of compressed Java and web module files ( was files ).

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Q1465. Name few interfaces that extends Collection Interface ?

Ans. http://www.buggybread.com/2015/02/java-collections-interfaces-that.html

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Q1466. 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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Q1467. Name few classes that extend Thread class ?

Core Java

Ans. http://www.buggybread.com/2015/02/java-threads-classes-that-inherit.html

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Q1468. Name few classes that extends Collections class ?

Ans. http://www.buggybread.com/2015/02/java-collections-classes-that-inherit.html

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Q1469. Name few Date and Time Classes you have used in your projects ?

Ans. http://www.buggybread.com/2015/02/java-util-date-time-classes-and.html

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Q1470. Name few Calendar related classes and Interfaces ?

Ans. http://www.buggybread.com/2015/02/java-util-calendar-classes-and.html

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Q1471. Name few abstract classes of Java collections framework ?

Ans. http://www.buggybread.com/2015/02/java-collections-abstract-classes.html

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Q1472. Name few classes that implement Cloneable interface ?

Ans. http://www.buggybread.com/2015/02/java-collections-classes-that-implement_58.html

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Q1473. Name few classes that implement Set interface ?

Ans. http://www.buggybread.com/2015/02/java-collections-classes-that-implement_78.html

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Q1474. Name few classes that implement iterable interface ?

Ans. http://www.buggybread.com/2015/02/java-collections-classes-that-implement_45.html

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Q1475. Name few classes that implement Map interface ?

Ans. http://www.buggybread.com/2015/02/java-collections-classes-that-implement_82.html

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Q1476. Name few classes that implement List interface ?

Ans. http://www.buggybread.com/2015/02/java-collections-classes-that-implement_35.html

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Q1477. Name few classes that implement Queue interface ?

Ans. http://www.buggybread.com/2015/02/java-collections-classes-that-implement_1.html

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Q1478. Name few classes that implement Collection interface ?

Ans. http://www.buggybread.com/2015/02/java-collections-classes-that-implement.html

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Q1479. Name few classes java provides for File compression ?

Ans. http://www.buggybread.com/2015/01/java-zip-classes-and-interfaces.html

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Q1480. Name few Buffered IO classes and interfaces ?

Ans. http://www.buggybread.com/2015/01/java-io-buffered-classes-and-interfaces.html

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