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Q431. Difference between Scanner and BufferedReader ? Which one is faster and Why ?

Ans. Scanner is used for parsing tokens from the contents of the stream while BufferedReader just reads the stream.

BufferedReader read files efficiently by using a buffer to avoid physical disk operations.

Buffer size of Scanner is usually smaller than the Buffered Writer.

BufferedReader is faster that Scanner as it just reads the Stream and doesn't Parse the tokens to read the stream into primitive data types.

Sample Code for Scanner

Sample Code for BufferedReader

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Rarely asked as it was introduced with Java 8.

Q432. 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.

Q433. What are the errors identified by DocLint ?

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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Q434. Why Java uses Unicode System ?

Ans. Before Unicode there were many language / country standards like ASCII , ISO , KOI and BIG 5. In order to accommodate multiple language letters and to overcome problems with using different multiple standards , a new language standard was developed i.e unicode system.

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Q435. What is the difference between out.println(a+b); and out.println (a+" " +b); in Java? with a=2 and b=1

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

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Q436. Which sorting algorithm is used by Collections.sort() in Java ?

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

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Q437. What is the difference between Data Type and Data Structure ?

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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Q438. 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"));

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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Q439. Which takes more memory - float or Float ?

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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Q440. What is collision in hash collections ?

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

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Q441. 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);

Ans. truefalse

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Q442. What is OutOfMemoryError in 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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Q443. Which interface does java.util.Hashtable implement ?

a. List
b. Set
c. Collection
d. Map

Ans. Map

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Q444. Which of the collections allows null as the key ?

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

Ans. HashMap

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Q445. Strings in switch were introduced in Which Java version ? a. Java 5 b. Java 6 c. Java 7 d. Java

Ans. Java 7

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Rarely asked as it was introduced with Java 8.

Q446. Which keyword specify that a variable is effectively final ? a. final b. No Keyword c. Both of the above d. None of the above

Ans. No Keyword

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Rarely asked as it was introduced with Java 8.

Q447. Which of the following has been introduced with Java 8 ? a. StringBuffer b. StringBuilder c. StringFilter d. StringJoiner

Ans. StringJoiner

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Q448. What is GregorianCalendar class ?

Ans. This class provides support for traditional Western calendars.

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Q449. What are fail-fast Iterators ?

Ans. Fail-fast iterators detect illegal concurrent modification during iteration and fail quickly and cleanly rather than risking arbitrary, non deterministic behavior at an undetermined time in future. Example could be of an Iterator failing if it smells ConcurrentModificationException.

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Q450. Print natural numbers sequentially with two threads.

Ans. http://stackoverflow.com/questions/18799591/print-natural-sequence-with-help-of-2-threads1-is-printing-even-and-2nd-is-pri

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Frequently asked in face to face interviews.

Q451. Write a program to print fibonacci series.

Ans. int count = 15;
int[] fibonacci = new int[count];
fibonacci[0] = 0;
fibonacci[1] = 1;
for(int x=2; x < count; x++){
fibonacci[x] = fibonacci[x-1] + fibonacci[x-2];
}

for(int x=0; x< count; x++){
System.out.print(fibonacci[x] + " ");
}

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Q452. What is the use of Synchronized block ?

Ans. The goal of a synchronised block is to achieve mutual exclusion i.e at one time, the segment of the code should be executed by single thread only and hence the lock needs to be retrieved before executing the segment and then released.

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Must know at all levels. Among Top 10 frequently asked questions in Java. Very frequently asked to fresh graduates or less experienced professionals.

Q453. What is Inheritance ?

Ans. Its a facility for code reuse and independent extension wherein a derived class inherits the properties of parent class.

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Q454. What is ADT or Abtstract Data Type ?

Ans. ADT is a container which holds different types of objects with specifications.

For example - Stack, Array, Liked list, Tree

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Q455. Write a method to convert all elements of a set to lower case.

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?keyword=Method+to+convert+all+elements+of+a+collection&category=code

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Q456. Write java code to Get all words from a String and display them

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?keyword=+Get+all+words+from+a+String&category=code

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Q457. Write a Method to get a map of words and their count by passing in the string

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?keyword=Method+to+get+a+map+of+words&category=code

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Q458. How is static and dynamic polymorphism achieved in Java ?

Ans. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding.

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Q459. Why can't we declare a class abstract as well as final ?

Ans. Abstract means that the class is only meant to be subclassed whereas final means that it cannot be subclassed so both concepts - abstract and final are actually mutually exclusive and hence not permitted together.

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Very frequently asked to fresh graduates. Frequently asked in NSEiT and Accenture India

Q460. Write a program to Generate prime numbers till a given number

Ans. public class Main {
public static void main(String args[]) {
int number = 2;
int count = 0;
long sum = 0;
int givenNumber = 1000;
while (count < givenNumber) {
if (isPrimeNumber(number)) {
sum = number;
count;
}
number;
}
System.out.println(sum);
}
private static boolean isPrimeNumber(int number) {
for (int i = 2; i <= number / 2; i) {
if (number % i == 0) {
return false;
}
}
return true;
}
}

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