Checking if a number is a power of 2

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If an integer x is a power of 2, only one bit is set, whereas x-1 has all bits set after that. For example: 4 is 100 and 3 is 011 as binary number, which satisfies the aforementioned condition. Zero is not a power of 2 and has to be checked explicitly.

boolean isPowerOfTwo(int x)
{
   return (x != 0) && ((x & (x - 1)) == 0);
}

Usage for Left and Right Shift

Let’s suppose, we have three kind of permissions, READ, WRITE and EXECUTE. Each permission can range from 0 to 7. (Let’s assume 4 bit number system)

RESOURCE = READ WRITE EXECUTE (12 bit number)
RESOURCE = 0100 0110 0101 = 4 6 5 (12 bit number)

How can we get the (12 bit number) permissions, set on above (12 bit number)?

0100 0110 0101
0000 0000 0111 (&)
0000 0000 0101 = 5

So, this is how we can get the EXECUTE permissions of the RESOURCE. Now, what if we want to get READ permissions of the RESOURCE?

0100 0110 0101
0111 0000 0000 (&)
0100 0000 0000 = 1024

Right? You are probably assuming this? But, permissions are resulted in 1024. We want to get only READ permissions for the resource. Don’t worry, that’s why we had the shift operators. If we see, READ permissions are 8 bits behind the actual result, so if apply some shift operator, which will bring READ permissions to the very right of the result? What if we do:

0100 0000 0000 >> 8 => 0000 0000 0100 (Because it’s a positive number so replaced with 0’s, 
if you don’t care about sign, just use unsigned right shift operator)

We now actually have the READ permissions which is 4.

Now, for example, we are given READ, WRITE, EXECUTE permissions for a RESOURCE, what can we do to make permissions for this RESOURCE?

Let’s first take the example of binary permissions. (Still assuming 4 bit number system)

READ = 0001
WRITE = 0100
EXECUTE = 0110

If you are thinking that we will simply do:

READ | WRITE | EXECUTE, you are somewhat right but not exactly. See, what will happen if we will perform READ | WRITE | EXECUTE

0001 | 0100 | 0110 => 0111

But permissions are actually being represented (in our example) as 0001 0100 0110

So, in order to do this, we know that READ is placed 8 bits behind, WRITE is placed 4 bits behind and PERMISSIONS is placed at the last. The number system being used for RESOURCE permissions is actually 12 bit (in our example). It can(will) be different in different systems.

(READ << 8) | (WRITE << 4) | (EXECUTE)
0000 0000 0001 << 8 (READ)
0001 0000 0000 (Left shift by 8 bits)
0000 0000 0100 << 4 (WRITE)
0000 0100 0000 (Left shift by 4 bits)
0000 0000 0001 (EXECUTE)

Now if we add the results of above shifting, it will be something like;

0001 0000 0000 (READ)
0000 0100 0000 (WRITE)
0000 0000 0001 (EXECUTE)
0001 0100 0001 (PERMISSIONS)

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Basic Programs

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• Creating Your First Java Program
• Type Conversion
• Getters and Setters
• Reference Data Types
• Java Compiler - javac
• Documenting Java Code
• Command line Argument Processing
• Java Command - java and javaw
• Literals
• Primitive Data Types

Strings in Java

• Comparing Strings
• Changing the case of characters within a String
• Finding a String Within Another String
• String pool and heap storage
• Splitting Strings
• Joining Strings with a delimiter and Reversing Strings
• String concatenation and StringBuilders
• Substrings and Platform Independent new line Separator
• Adding toString() method for custom objects
• Remove Whitespace from the Beginning and End of a String and Case insensitive switch
• Replacing parts of Strings and Getting the nth character in a String
• Counting occurrences of a substring or character in a string

StringBuffer and StringBuilder

• String Buffer
• String Builder
• String Tokenizer and Splitting a string into fixed length parts

Date Class

• Convert java.util.Date to java.sql.Date and Basic date
• LocalDate and LocalDateTime objects
• Creating a Specific Date and Converting Date to String format
• Convert formatted string representation of date to Date object
• Comparing Date objects
• Converting String into Date and Time Zones and java.util.Date

Dates and Time (java.time.*)

• Dates and Time
• Date Time Formatting and Date Manipulations
• LocalTime

BigDecimal

• Comparing and Using BigDecimals
• BigDecimal.valueOf()
• Mathematical operations with BigDecimal

BigInteger

• Initialization and Generating random BigIntegers
• BigInteger Mathematical Operations Examples
• NumberFormat

Bit Manipulation

• Checking, setting, clearing, and toggling individual bits. Using long as bit mask
• Checking if a number is a power of 2
• Signed vs unsigned shift and Expressing the power of 2

Arrays

• Creating and Initializing Arrays
• Creating a List from an Array
• Multidimensional and Jagged Arrays
• Array Covariance and Arrays to Stream
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• Primitives and boxed types and Remove an element from an array
• Comparing arrays for equality and Copying arrays

Collections

• Removing items from a List within a loop
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Lists

• Sorting a generic list
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Sets

• Initialization and Basics of Set
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Maps

• Iterating Map Entries Effciently
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TreeMap and TreeSet

• TreeMap and TreeSet of a simple Java type
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Queues and Deques

• Usage of the Queue and Deque
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Enums

• Declaring and using a basic enum
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Operators

• Increment/Decrement and Conditional Operator
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Constructors

• Default and Call parent Constructor

Object Class Methods and Constructor

• hashCode() method
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Annotations

• Defining annotation types
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Immutable Class

• What is the advantage of immutability and Rules and Example

Immutable Objects

• Creating an immutable version of a type using defensive copying
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Visibility (controlling access to members of a class)

• Private ,Public ,Package and Protected Visibility

Generics

• Creating a Generic Class
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Classes and Objects

• Method Overloading and Overriding
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Nested and Inner Classes

• Static vs Non Static Nested Classes
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The java.util.Objects Class

• Basic use for object null check and Objects.nonNull() method

Default Methods

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Packages

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Reference Types

• Different Reference Types

Console I/O

• Reading user input from the console
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Streams

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InputStreams and OutputStreams

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Readers and Writers

• BufferedReader and StringWriter Example

Preferences

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Collection Factory Methods

• List<E>, Set<E> and Map<K, V> Factory Method Examples

Alternative Collections

• Multimap in Guava, Apache and Eclipse Collections
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• Compare operation with collections - Create collections

Concurrent Collections

• Insertion into ConcurrentHashMap, Thread-safe and Concurrent Collections

super keyword

• Super keyword use with examples

Serialization

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Optional

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Object References

• Object References as method parameters

Exceptions and exception handling

• Catching an exception with try-catch
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Calendar and its Subclasses

• Creating, Subtracting and Finding AM/PM Calendar

Using the static keyword

• Reference to non-static member from static context

Properties Class

• Reference to non-static member from static context

Lambda Expressions

• Introduction to Java lambdas
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• Memory utilization, own functional interface and Traditional style to Lambda
• return only returns from the lambda and Execute-around Pattern

Basic Control Structures

• Switch, do while, For Each, Continue Statement in Java
• If, Else If, Else Control, For Loops and Ternary Operator
• Try-Catch-Finally, Break, While Loops, If Else and Nested break / continue

BufferedWriter

• Write a line of text to File

New File I/O

• Creating paths, Manipulating, Retrieving, Reading and Writing files

File I/O

• Migrating from java.io.File to Java 7 NIO
• Reading an image, File Read/Write, Reading all bytes and Copying a file
• Stream vs Writer/Reader API and Reading a file with a Scanner
• Copying a file using InputStream and OutputStream
• Blocking or redirecting standard output / error
• Reading a file using BufferedInputStream

Scanner

• General Pattern that does most commonly asked about tasks
• Custom delimiters, Reading system input and Reading file input using Scanner

Interfaces

• Implementing multiple interfaces, Declaring and Implementing an Interface
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• Using Interfaces with Generics and Strengthen bounded type parameters

Regular Expressions

• Using capture groups and Escape Characters
• Matching a backslash, Not matching string and Matching with a regex literal

Comparable and Comparator

• Sorting a List using Comparable<T> or a Comparator<T>
• compareTo, compare Methods and Natural vs explicit sorting

Java Floating Point Operations

• Comparing floating point values
• OverFlow and UnderFlow, Formatting the floating point values

Currency and Money

• Add custom currency

Object Cloning

• Cloning performing a deep copy and copy factory
• Cloning using a copy constructor and implementing Clonable interface

Recursion

• Basic idea of Recursion
• StackOverflowError & recursion to loop
• Computing the Nth Fibonacci Number and power of a number

Converting to and from Strings

• Converting String to other datatypes
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Random Number Generation

• Pseudo Random Numbers in Specific Range
• Generating Random Numbers with a Specified Seed

Singletons

• Enum Singleton and Singleton without use of Enum, Thread safe Singleton
• Extending singleton (singleton inheritance)

Autoboxing

• Using int and Integer interchangeably and Auto-unboxing may lead to NullPointerException
• Different Cases When Integer and int can be used interchangeably

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