Interview Questions and Answers for 'T' | Search Interview Question

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Rarely asked as it was introduced with Java 8.

Q901. What is DocLint in Java 8 ?

Ans. DocLint Provide a means to detect errors in Javadoc comments early in the development cycle and in a way that is easily linked back to the source code.

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Rarely asked as it was introduced with Java 8.

Q902. What are the errors identified by DocLint ?

Core Java

Ans. Bad syntax, such as unescaped characters or unmatched parentheses

Bad HTML, such as invalid or missing tags or attributes

Bad references, such as referencing a non-existent type with @see

Accessibility errors, such as a missing summary or caption from a table

Missing info, such as an undocumented parameter

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Q903. What is the difference between out.println(a+b); and out.println (a+" " +b); in Java? with a=2 and b=1

Core Java

Ans. First will give the ouput as 3 and the second will give output as 2 1

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Q904. Which sorting algorithm is used by Collections.sort() in Java ?

Core Java

Ans. The sorting algorithm is a modified mergesort. This algorithm offers guaranteed n log(n) performance.

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Q905. What doesn Http keep alive header does ?

Java EE

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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Q906. 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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Q907. 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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Q908. 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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Q909. 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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Q910. 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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Q911. 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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Q912. 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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Q913. Which tree is used to implement TreeMap in Java?

Ans. Red Black Tree

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Q914. 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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Q915. 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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Q916. What will the following code result ?

List> intList = new ArrayList>();

intList.add(Optional.empty());
intList.add(Optional.of(2));
intList.add(Optional.of(3));
intList.add(Optional.of(4));

System.out.println(intList.get(null));

Ans. Compile time error at last line as the get method expect argument of type native int.

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Q917. What will the following code result ? Will it compile ?

List> intList = new ArrayList>();

intList.add(Optional.empty());
intList.add(Optional.of(2));
intList.add(Optional.of(3));
intList.add(Optional.of(4));

System.out.println(intList.get((Integer)null));

Ans. Yes but the last line will throw NullPointerException upon execution.

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Q918. 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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Q919. 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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Q920. 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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Q921. What is Apache Kafka ?

BigData

Ans. Kafka is a distributed, partitioned, replicated commit log service. It provides the functionality of a messaging system through messages being written to logs.

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Q922. What is a broker in Apache Kafka ?

Ans. Kafka is run as a cluster comprised of one or more servers each of which is called a broker

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Q923. What is a Topic in Apache Kafka ?

Ans. A topic is a category or feed name to which messages are published

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Q924. 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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Q925. 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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Q926. Does Kafka uses ZooKeeper ?

Ans. Yes

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Q927. Which interfaces are implemented by BatchUpdateException?

Ans. [Iterable]

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Q928. What is the package name for CertStoreParameters class?

Ans. java.lang

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Q929. Which is the Parent Class of CertStoreParameters class?

Ans. Clonable

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Q930. Action Class is singleton and hence not thread safe in ..

a. All versions of Struts
b. Struts 1
c. Struts 2
d. None of Struts versions

Ans. Struts 1

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