Stacks and BlockingQueue

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Stacks

What is a Stack?

In Java, Stacks are a LIFO (Last In, First Out) Data structure for objects.

Stack API

Java contains a Stack API with the following methods

Stack() //Creates an empty Stack
isEmpty() //Is the Stack Empty? Return Type: Boolean
push(Item item) //push an item onto the stack
pop() //removes item from top of stack Return Type: Item
size() //returns # of items in stack Return Type: Int

Example

import java.util.*;
 
public class CustomStackExample {
    public static void main(String args[]) {
        Stack customStack = new Stack();
        System.out.println("Custom stack: " + customStack);
 
        customStack.push(5);
        System.out.println("5 was pushed to the custom stack");
        System.out.println("Custom stack: " + customStack);
 
        customStack.push(8);
        System.out.println("8 was pushed to the custom stack");
        System.out.println("Custom stack: " + customStack);
 
        customStack.push(20);
        System.out.println("20 was pushed to the custom stack");
        System.out.println("Custom stack: " + customStack);
 
        customStack.pop();
        System.out.println("20 was popped from the custom stack");
        System.out.println("Custom stack: " + customStack);
 
        customStack.pop();
        System.out.println("8 was popped from the custom stack");
        System.out.println("Custom stack: " + customStack);
 
        customStack.pop();
        System.out.println("5 was popped from the custom stack");
        System.out.println("Custom stack: " + customStack);
 
        if (customStack.isEmpty()) {
            System.out.println("Empty custom stack");
        }
    }
}

Output

Custom stack: []
5 was pushed to the custom stack
Custom stack: [5]
8 was pushed to the custom stack
Custom stack: [5, 8]
20 was pushed to the custom stack
Custom stack: [5, 8, 20]
20 was popped from the custom stack
Custom stack: [5, 8]
8 was popped from the custom stack
Custom stack: [5]
5 was popped from the custom stack
Custom stack: []
Empty custom stack

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BlockingQueue

A BlockingQueue is an interface, which is a queue that blocks when you try to dequeue from it and the queue is empty, or if you try to enqueue items to it and the queue is already full. A thread trying to dequeue from an empty queue is blocked until some other thread inserts an item into the queue. A thread trying to enqueue an item in a full queue is blocked until some other thread makes space in the queue, either by dequeuing one or more items or clearing the queue completely.

BlockingQueue methods come in four forms, with different ways of handling operations that cannot be satisfied immediately, but may be satisfied at some point in the future: one throws an exception, the second returns a special value (either null or false, depending on the operation), the third blocks the current thread indefinitely until the operation can succeed, and the fourth blocks for only a given maximum time limit before giving up.

A BlockingQueue can be bounded or unbounded. A bounded BlockingQueue is one which is initialized with initial capacity.

BlockingQueue<String> bQueue = new ArrayBlockingQueue<String>(2);

Any calls to a put() method will be blocked if the size of the queue is equal to the initial capacity defined.

An unbounded Queue is one which is initialized without capacity, actually by default it initialized with Integer.MAX_VALUE.

Some common implementations of BlockingQueue are:

• ArrayBlockingQueue
• LinkedBlockingQueue
• PriorityBlockingQueue

Now let's look at an example of ArrayBlockingQueue:

import java.util.concurrent.*;
 
public class BlockingQueueExample {
    public static void main(String[] args) throws InterruptedException {
        BlockingQueue<String> queue = new ArrayBlockingQueue<>(2);
 
        queue.put("First item");
        System.out.println("First item added");
 
        queue.put("Second item");
        System.out.println("Second item added");
 
        queue.put("Third item");
        System.out.println("Third item added");
    }
}

Output

First item added
Second item added

And the thread will be blocked after the second output.

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Basic Programs

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• Creating Your First Java Program
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• Reference Data Types
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Strings in Java

• Comparing Strings
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• Remove Whitespace from the Beginning and End of a String and Case insensitive switch
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• Counting occurrences of a substring or character in a string

StringBuffer and StringBuilder

• String Buffer
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Date Class

• Convert java.util.Date to java.sql.Date and Basic date
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• 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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• Immutable Empty , Sub and Unmodifiable Collection
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• Creating your own Iterable structure for use with Iterator or for-each loop

Lists

• Sorting a generic list
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• Creating, Adding and Removing element from an ArrayList
• 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
• Creating and Initializing Maps
• 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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• TreeMap and TreeSet Thread Safety

Queues and Deques

• Usage of the Queue and Deque
• Stacks and BlockingQueue
• LinkedList as a FIFO Queue and Queue Interface
• Dequeue Interface

Enums

• Declaring and using a basic enum
• Enums with constructors and Abstract Methods
• Implements Interface and Singleton pattern
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Operators

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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
• Typical design flaws which prevent a class from being immutable

Visibility (controlling access to members of a class)

• Private ,Public ,Package and Protected Visibility

Generics

• Creating a Generic Class
• Diamond and Declaring a Generic Method
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Classes and Objects

• Method Overloading and Overriding
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• Basic Object Construction and Use

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

• Why Use, Usage and Accessing overridden of default methods
• interface methods, multiple inheritance and Abstract class

Packages

• Using Packages to create classes and Protected Scope

Inheritance

• What is Inheritance
• Abstract Classes
• Abstract class and Interface usage
• Programming to an interface
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Reference Types

• Different Reference Types

Console I/O

• Reading user input from the console
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Streams

• Using Streams
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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
• Apache HashBag, Guava HashMultiset and Eclipse HashBag
• 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

• Map,Return default value and Throw an exception
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Object References

• Object References as method parameters

Exceptions and exception handling

• Catching an exception with try-catch
• The try-with-resources statement
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• Introduction and Return statements in try catch block
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• Creating and reading stacktraces
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• try-catch-finally statements and throws clause in a method declaration

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
• 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
• Usefulness of interfaces and Default methods
• 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
• Converting other datatypes to String

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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