Date Time Formatting and Date Manipulations

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Date Time Formatting

Before Java 8, there was DateFormat and SimpleDateFormat classes in the package java.text and this legacy code will be continued to be used for sometime

But, Java 8 offers a modern approach to handling Formatting and Parsing.

In formatting and parsing first you pass a String object to DateTimeFormatter, and in turn use it for formatting or parsing.

import java.time.*;
import java.time.format.*;
 
class DifferentDateTimeFormat {
    public static void main(String[] args) {
        // Parsing
        String pattern = "MM-dd-yyyy HH:mm";
        DateTimeFormatter customFormatter = DateTimeFormatter.ofPattern(pattern);
 
        LocalDateTime defaultDateTime = LocalDateTime.parse("2019-07-15T09:30"); // Default format
        LocalDateTime customFormattedDateTime = LocalDateTime.parse("07-25-2023 14:45", customFormatter);
 
        System.out.println(defaultDateTime + "\n" + customFormattedDateTime); // Will be printed in default format
 
        // Formatting
        DateTimeFormatter customFormat = DateTimeFormatter.ofPattern("EEEE, MMMM d, yyyy HH:mm");
 
        DateTimeFormatter isoFormat = DateTimeFormatter.ISO_LOCAL_DATE_TIME;
        LocalDateTime now = LocalDateTime.now();
 
        System.out.println(now.format(customFormat) + "\n" + now.format(isoFormat));
    }
}

An important notice, instead of using Custom patterns, it is good practice to use predefined formatters. Your code look more clear and usage of ISO8061 will definitely help you in the long run.

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Simple Date Manipulations

Get the current date.

LocalDate.now()

Get yesterday's date.

LocalDate y = LocalDate.now().minusDays(1);

Get tomorrow's date

LocalDate t = LocalDate.now().plusDays(1);

Get a specific date.

LocalDate t = LocalDate.of(1974, 6, 2, 8, 30, 0, 0);

In addition to the plus and minus methods, there are a set of "with" methods that can be used to set a particular field on a LocalDate instance.

LocalDate.now().withMonth(6);

The example above returns a new instance with the month set to June (this differs from java.util.Date where setMonth was indexed a 0 making June 5).

Because LocalDate manipulations return immutable LocalDate instances, these methods may also be chained together.

LocalDate ld = LocalDate.now().plusDays(1).plusYears(1);

This would give us tomorrow's date one year from now.

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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
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Collections

• Removing items from a List within a loop
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Lists

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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

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Queues and Deques

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Enums

• Declaring and using a basic enum
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Operators

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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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Generics

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Classes and Objects

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The java.util.Objects Class

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Collection Factory Methods

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Alternative Collections

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Concurrent Collections

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super keyword

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Optional

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Object References

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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
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• Stream vs Writer/Reader API and Reading a file with a Scanner
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Scanner

• General Pattern that does most commonly asked about tasks
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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
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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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