Java

Question 1

How to create a char array from a String?

Answer 1

String str = “123445”;

char[] arr = str.toCharArray();

Question 2

How to get an String from a value of a different type?

Answer 2

String str = String.valueOf(1234);
or
Integer.toString(int i, int radix); Integer.toString(int i);

Question 3

What are the bitwise operations in Java?

Answer 3

& (bitwise and)
| (bitwise or)
^ (bitwise XOR)
~ (bitwise compliment)
>>> (Fill with zero left)
>> (fill with highest bit on the left - sign)

Question 4

How to isolate the lowerst bit that is 1 in X?

Answer 4

x &~(x-1)
x= 00101100 ;
y = x &~(x-1);
y = 0000100;

Question 5

What are the primitive data types in java?

Answer 5

byte, short, int, long, float, double, boolean, char

Question 6

What are the sizes of the primitive java types?

Answer 6

byte = 8 bit signed
short = 16 bit signed
int = 32 bit signed (Unsigned too in Java 8)
long = 64 signed (Unsigned too in Java 8)
float = 32 bit IEEE 754 precisions
double = 64 bit IEEE 754 precisions
boolean = Not defined
char = 16 bit unicode

Question 7

How can integer literals be represented in java?

Answer 7

// The number 26, in decimal
int decVal = 26;
//  The number 26, in hexadecimal
int hexVal = 0x1a;
// The number 26, in binary
int binVal = 0b11010;

Question 8

How can Floating-Point Literals be represented in java?

Answer 8

double d1 = 123.4;
// same value as d1, but in scientific notation
double d2 = 1.234e2;
float f1  = 123.4f;

Question 9

How to separate long numbers in java 7?

Answer 9

You can use underscore:
long creditCardNumber = 1234_5678_9012_3456L;
long socialSecurityNumber = 999_99_9999L;
float pi = 3.14_15F;
long hexBytes = 0xFF_EC_DE_5E;
long hexWords = 0xCAFE_BABE;
long maxLong = 0x7fff_ffff_ffff_ffffL;
byte nybbles = 0b0010_0101;
long bytes = 0b11010010_01101001_10010100_10010010;

Question 10

How to get the absolute number in java?

Answer 10

Math.abs(value)

It’s static and works for long, int, float and double

Question 11

How to get a logarithm base 10?

Answer 11

Math.log10(double value)

Question 12

How to get the maximum between 2 values?

Answer 12

Math.max(value)

It’s static and works for double, long, float and int

Question 13

How to get the minimum between 2 values?

Answer 13

Math.min(value)

It’s static and works for double, long, float and int

Question 14

How to raise a to a power in java?

Answer 14

Math.pow(double a, double b)

Question 15

How to get the square root of a number in java?

Answer 15

Math.sqrt(double a)

Question 16

Which collection classes are synchronized or thread-safe ?

Answer 16

Stack, Properties , Vector and Hashtable

Question 17

What is the difference between List and Set ?

Answer 17

Set contain only unique elements while List can contain duplicate elements.
Set is unordered while List is ordered . List maintains the order in which the objects are added .

Question 18

What is the difference between Map and Set ?

Answer 18

Map object has unique keys each containing some value, while Set contain only unique values.

Question 19

What do you understand by iterator fail-fast property?

Answer 19

terator fail-fast property checks for any modification in the structure of the underlying collection everytime we try to get the next element. If there are any modifications found, it throws ConcurrentModificationException. All the implementations of Iterator in Collection classes are fail-fast by design except the concurrent collection classes like ConcurrentHashMap and CopyOnWriteArrayL

Question 20

What is difference between fail-fast and fail-safe?

Answer 20

Iterator fail-safe property work with the clone of underlying collection, hence it’s not affected by any modification in the collection. By design, all the collection classes in java.util package are fail-fast whereas collection classes in java.util.concurrent are fail-safe.
Fail-fast iterators throw ConcurrentModificationException whereas fail-safe iterator never throws ConcurrentModificationException.

Question 21

What is BlockingQueue

Answer 21

java.util.concurrent.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.

BlockingQueue interface is part of java collections framework and it’s primarily used for implementing producer consumer problem. We don’t need to worry about waiting for the space to be available for producer or object to be available for consumer in BlockingQueue as it’s handled by implementation classes of BlockingQueue.

Java provides several BlockingQueue implementations such as ArrayBlockingQueue, LinkedBlockingQueue, PriorityBlockingQueue, SynchronousQueue etc.