Using long as bit mask

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Checking, setting, clearing, and toggling individual bits. Using long as bit mask

Assuming we want to modify bit n of an integer primitive, i (byte, short, char, int, or long):

(i & 1 << n) != 0 // checks bit 'n'
i |= 1 << n; // sets bit 'n' to 1
i &= ~(1 << n); // sets bit 'n' to 0
i ^= 1 << n; // toggles the value of bit 'n'

Using long/int/short/byte as a bit mask:

public class BitMaskExample {
    private static final long BIT_1 = 1L << 0;
    private static final long BIT_2 = 1L << 1;
    private static final long BIT_3 = 1L << 2;
    private static final long BIT_4 = 1L << 3;
    private static final long BIT_5 = 1L << 4;
    private static final long BIT_60 = 1L << 59;
 
    public static void main(String[] args) {
        checkBitMask(BIT_1 | BIT_3 | BIT_5 | BIT_60);
    }
 
    private static void checkBitMask(long bitmask) {
        System.out.println("BIT_1: " + ((bitmask & BIT_1) != 0));
        System.out.println("BIT_2: " + ((bitmask & BIT_2) != 0));
        System.out.println("BIT_3: " + ((bitmask & BIT_3) != 0));
        System.out.println("BIT_4: " + ((bitmask & BIT_4) != 0));
        System.out.println("BIT_5: " + ((bitmask & BIT_5) != 0));
        System.out.println("BIT_60: " + ((bitmask & BIT_60) != 0));
    }
}

Result:

BIT_1: true
BIT_2: false
BIT_3: true
BIT_4: false
BIT_5: true
BIT_60: true

which matches that mask we passed as checkBitMask parameter: BIT_1 | BIT_3 | BIT_5 | BIT_60

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java.util.BitSet class

Since 1.7 there's a java.util.BitSet class that provides simple and user-friendly bit storage and manipulation interface:

final BitSet set1 = new BitSet(8); // by default all bits are unset
 
IntStream.range(0, 8).filter(i -> i % 2 == 0).forEach(set1::set); // {0, 2, 4, 6}
 
set1.set(3); // {0, 2, 3, 4, 6}
 
set1.set(3, false); // {0, 2, 4, 6}
 
final boolean check1 = set1.get(3); // check1 = false
 
set1.flip(6); // {0, 2, 4}
 
set1.set(100); // {0, 2, 4, 100} - expands automatically

BitSet implements Clonable and Serializable, and under the hood all bit values are stored in long[] words field, that expands automatically.

It also supports whole-set logical operations and, or, xor, andNot:

final BitSet setA = new BitSet(8);
final BitSet setB = new BitSet(8);
final BitSet setC = new BitSet(8);
final BitSet setD = new BitSet(8);
 
setA.and(new BitSet(8)); // Performs AND operation with an empty BitSet
setB.or(new BitSet(8)); // Performs OR operation with an empty BitSet
setC.xor(new BitSet(8)); // Performs XOR operation with an empty BitSet
setD.andNot(new BitSet(8)); // Performs AND-NOT operation with an empty BitSet

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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
• Iterating over arrays
• Sorting arrays and Length of an Array
• Finding an element in an array nd change the size of an array
• 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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• ArrayList and adding objects and Iterating over Collections
• Immutable Empty , Sub and Unmodifiable Collection
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Lists

• Sorting a generic list
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• Positional Access Operations and Iterating over elements in a list

Sets

• Initialization and Basics of Set
• Types and Usage of Sets

Maps

• Iterating Map Entries Effciently
• Using Default Methods of Map from Java 8
• Usage of HashMap and Iterating through the contents of a Map
• Merging, combine and composing Maps and Add multiple items
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• Check if key exists, Add an element and Clear the map
• LinkedHashMap, WeakHashMap and SortedMap

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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• LinkedList as a FIFO Queue and Queue Interface
• Dequeue Interface

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

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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)

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Generics

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Classes and Objects

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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

• Using Packages to create classes and Protected Scope

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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

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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

• Basic and Custom 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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• Introduction and Return statements in try catch block
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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
• Using Lambda Expressions to Sort a Collection
• Implementing multiple interfaces, Listener and Java Closures with lambda expressions
• 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
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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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