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AWS

May 19, 2023 Permissions 0777 for 'your_key.pem' are too open
Dec 17, 2022 How to link domain's name server to AWS Route 53
Oct 25, 2022 How to upload files to S3 on Spring Boot project (from set-up to controller)
Sep 28, 2022 A MUST check when setting up AWS RDS (or you will get Fatal Error 3000:0 - No such database found)
Sep 19, 2022 How to deploy Spring jar app to AWS

Ajax

Jun 03, 2023 Ajax button not showing up

Binary Search

Bitmask

Jul 08, 2023 Programmers 2차원 동전 뒤집기
Jul 07, 2023 Programmers 2개 이하로 다른 비트

Data structure & Algorithms

Jul 08, 2023 Programmers 2차원 동전 뒤집기
Jul 07, 2023 Programmers 2개 이하로 다른 비트
Jul 06, 2023 Programmers 기능개발
Jul 05, 2023 Programmers 같은 숫자는 싫어
Jul 04, 2023 Programmers 선입 선출 스케줄링
Jul 03, 2023 Programmers 선입 선출 스케줄링
Jul 02, 2023 Programmers 징검다리
Jul 01, 2023 Programmers 입국심사
May 08, 2023 String and methods in Python and practice questions
May 05, 2023 Difference between split() and strip() in Python
Apr 28, 2023 Floyd Warshall algorithm
Apr 25, 2023 Greedy algorithms and practice questions
Apr 21, 2023 Kruskal algorithm for minimal spanning tree (MST)
Apr 19, 2023 defaultdict(list) vs just dictionary
Apr 16, 2023 Sorting and practice questions
Apr 14, 2023 List and practice questions
Apr 10, 2023 Queue and practice questions
Apr 07, 2023 Stack (with deque) and practice questions
Apr 05, 2023 Dijkstra template and practice questions
Mar 27, 2023 Dictionary (+Counter) and practice questions
Mar 22, 2023 Using helper functions in python and updating return value
Mar 20, 2023 List index out of range (list initialised wrong!)
Mar 14, 2023 List as method argument and parameter in Python
Mar 12, 2023 Appending return value to list in Python
Mar 10, 2023 Python coding test prep for Java main users
Mar 08, 2023 Appending list to list in Python will not work
Jan 28, 2023 What is ArrayList<Integer>[] or StringBuilder[]? What is this square bracket's role?
Jan 16, 2023 Java regex
Jan 09, 2023 Useful Java data conversion tricks
Jan 06, 2023 Bucket sort
Dec 30, 2022 Useful Java data type functions for coding test
Dec 23, 2022 Sliding window
Dec 22, 2022 Quick union (not quick find)
Dec 17, 2022 String useful methods and practice questions
Dec 13, 2022 Use Deque over Stack in Java!
Dec 08, 2022 DFS and practice questions
Dec 04, 2022 General approach to backtracking + template
Dec 01, 2022 How to save time in for loop?
Nov 25, 2022 How to build graph with lambda?
Nov 21, 2022 Dynamic Programming error
Nov 18, 2022 Does HashMap allow duplicate keys when putting same key with different value?
Nov 15, 2022 How to convert ArrayList to array?
Nov 04, 2022 XOR in Leetcode string or character
Nov 01, 2022 Mistake in dealing with HashMap
Oct 30, 2022 5 main Dynamic Programming patterns and templates
Oct 28, 2022 Binary Search explained
Oct 11, 2022 Dynamic Programming explained
Sep 26, 2022 Java's ListNode in Leetcode
Sep 12, 2022 2 different ways to create 2D array (List vs ArrayList?)
Jun 27, 2022 TreeSet- HashSet with sorting capability
Jun 23, 2022 HashSet - Reference equality vs Object equality
Jun 20, 2022 Java's list, set and map
May 30, 2022 Java's StringBuilder
May 05, 2022 Difference between StringBuffer and StringBuilder
Mar 07, 2022 Difference between method size() and length()
Jan 07, 2022 Difference between Array and ArrayList
Jan 05, 2022 ArrayList

Database

Jun 06, 2023 What and how to use SQL coalesce
May 31, 2023 SQL Trigger and a possible error
May 27, 2023 Solve insertion type and select type at position 9 are not compatible error
May 10, 2023 Unique constraint error in Oracle db
May 01, 2023 What is SQL truncate? What is its use?
Mar 03, 2023 insert number does not match select in Querydsl JPA
Feb 06, 2023 Setting up H2 database

Docker

Sep 15, 2022 How to deploy Spring app (jar file) with Docker
Sep 12, 2022 docker push denied - requested access to the resource is denied
Aug 04, 2022 Docker's basic commands

Dynamic Programming

Oct 11, 2022 Dynamic Programming explained

General Knowledge

Dec 02, 2022 GarbageCollection in Java (feat. stack and Heap)
Nov 14, 2022 ASCII value in Java and how to store in array of size 128 or 256?
Oct 05, 2022 What is Object-oriented programming (OOP)?
Oct 03, 2022 SOLID principles of object-oriented design
Aug 02, 2022 Spring JAR vs WAR
Jul 17, 2022 IntelliJ Shortcut Windows
May 05, 2022 How long does object live?
Mar 11, 2022 When to add business logic to domain class, not service
Feb 23, 2022 Command Query Separation
Feb 18, 2022 The Stack and the Heap - where things live
Jan 12, 2022 How does Java code run? (feat. Compiler & JVM)
Jan 10, 2022 Difference between for and while loop

Git

Oct 17, 2022 Uploading your local source code to Github repo
Oct 15, 2022 How to use .gitignore to hide sensitive files in Spring Boot
Oct 12, 2022 Git upstream

H2

Feb 06, 2023 Setting up H2 database

Head First Java

Jan 12, 2023 Deducing ternary operator in Java
Jan 04, 2023 Double brace initialisation in Java
Dec 14, 2022 What is deadlock?
Dec 10, 2022 What is thread in Java? (feat. process)
Dec 02, 2022 GarbageCollection in Java (feat. stack and Heap)
Nov 29, 2022 How does reference variable work when adding it to list
Oct 23, 2022 Error in declaring variables in 1 line
Oct 07, 2022 Order of operator in Java (e.g. order matters in &&)
Sep 29, 2022 Careful with ternary operator
Sep 22, 2022 Problem of overflow with lambda
Sep 12, 2022 2 different ways to create 2D array (List vs ArrayList?)
Aug 14, 2022 Java nested class
Aug 01, 2022 try/catch finally flow control
Jul 28, 2022 Java's Exception handling
Jul 25, 2022 Java's Optional
Jul 21, 2022 Method reference to replace lambda expressions
Jul 14, 2022 Java Stream operation methods with examples
Jul 11, 2022 Java Stream with Lambda
Jul 07, 2022 Java Stream Matching its values
Jul 04, 2022 Java's Stream theory explained
Jul 01, 2022 Java's Convenience factory methods
Jun 27, 2022 TreeSet- HashSet with sorting capability
Jun 23, 2022 HashSet - Reference equality vs Object equality
Jun 20, 2022 Java's list, set and map
Jun 13, 2022 Java Lambda
Jun 09, 2022 Comparable, Comparator generics and Intro to Lambda
Jun 06, 2022 What is generics?
Jun 02, 2022 How to format numbers in Java (feat "%")
May 30, 2022 Primitive and how to wrap and unwrap (feat. ArrayList<Object>)
May 30, 2022 Java's StringBuilder
May 26, 2022 Final keyword on variable, method and class
May 09, 2022 Meaning of static variable and method and how to initialise them
May 05, 2022 How long does object live?
May 05, 2022 Difference between StringBuffer and StringBuilder
Mar 17, 2022 How to call a constructor from another constructor within the same class (not from subclass)
Mar 14, 2022 Role of superclass constructors in an object’s life
Mar 07, 2022 Difference between method size() and length()
Feb 21, 2022 Constructor
Feb 18, 2022 The Stack and the Heap - where things live
Feb 16, 2022 Invoking the superclass version of a method
Feb 14, 2022 How to differentiate class, a subclass, an abstract class or an interface?
Feb 10, 2022 Interface
Feb 07, 2022 Casting Polymorphism
Feb 03, 2022 Object Class polymorphism
Jan 27, 2022 Deeper knowledge on Polymorphism
Jan 24, 2022 Polymorphism
Jan 21, 2022 Inheritance
Jan 19, 2022 Encapsulation in Java
Jan 17, 2022 Difference between local and instance variables
Jan 14, 2022 Short-Circuit Operators ( && , || ) vs Non-Short-Circuit Operators ( &, | )
Jan 12, 2022 How does Java code run? (feat. Compiler & JVM)
Jan 10, 2022 Difference between for and while loop
Jan 07, 2022 Difference between Array and ArrayList
Jan 05, 2022 ArrayList

Http and Network

Nov 29, 2022 Applying SSL cert on AWS Load Balancer
Aug 04, 2022 TCP port
Apr 17, 2022 All about HTTP

Interview

Dec 30, 2022 Spring Interview Questions
Dec 30, 2022 Java Interview Questions

JPA

May 15, 2023 Different strategies of mapping PK (identity, sequence, automatic)
May 12, 2023 UniqueConstraints annotation and for multiple column conditions(제약조건) where Column annotation is insufficient
Apr 03, 2023 JPA cannot resolve column or table
Jan 31, 2023 JPA 양방향 연관관계 편의 메소드
Dec 23, 2022 JPA's Transactional and precautions
Sep 01, 2022 JPA 연관관계 편의 메서드
Aug 31, 2022 JPA force DB query when entity is already saved in 1st cache
Aug 25, 2022 JPA Table indexing
Aug 22, 2022 Spring Boot + JPA following Java's camelCase or DB's underscore when naming fields
Aug 19, 2022 JPA relationships in multi-module architecture (MSA)
Jun 02, 2022 What is entity and its precautions when designing in JPA?
May 12, 2022 JPA p6spy dependency to fill JPA ? gaps
May 02, 2022 JPA application.yml Hibernate settings explained
Mar 21, 2022 JPA cascade
Mar 05, 2022 JPA FetchType
Feb 28, 2022 Java inheritance in JPA
Feb 23, 2022 Command Query Separation

Java

Mar 24, 2023 return new String(array) when you modified array
Jan 12, 2023 Deducing ternary operator in Java
Jan 04, 2023 Double brace initialisation in Java
Dec 14, 2022 What is deadlock?
Dec 10, 2022 What is thread in Java? (feat. process)
Nov 29, 2022 How does reference variable work when adding it to list
Nov 14, 2022 ASCII value in Java and how to store in array of size 128 or 256?
Oct 23, 2022 Error in declaring variables in 1 line
Oct 07, 2022 Order of operator in Java (e.g. order matters in &&)
Oct 05, 2022 What is Object-oriented programming (OOP)?
Sep 29, 2022 Careful with ternary operator
Sep 27, 2022 Difference between ArrayList and LinkedList
Sep 22, 2022 Overloading method
Sep 22, 2022 Problem of overflow with lambda
Sep 17, 2022 Comparator VS Lambda
Aug 14, 2022 Java nested class
Aug 01, 2022 try/catch finally flow control
Jul 28, 2022 Java's Exception handling
Jul 25, 2022 Java's Optional
Jul 21, 2022 Method reference to replace lambda expressions
Jul 14, 2022 Java Stream operation methods with examples
Jul 11, 2022 Java Stream with Lambda
Jul 07, 2022 Java Stream Matching its values
Jul 04, 2022 Java's Stream theory explained
Jul 01, 2022 Java's Convenience factory methods
Jun 13, 2022 Java Lambda
Jun 09, 2022 Comparable, Comparator generics and Intro to Lambda
Jun 06, 2022 What is generics?
Jun 02, 2022 How to format numbers in Java (feat "%")
May 30, 2022 Primitive and how to wrap and unwrap (feat. ArrayList<Object>)
May 26, 2022 Final keyword on variable, method and class
May 09, 2022 Meaning of static variable and method and how to initialise them
May 05, 2022 How long does object live?
Mar 17, 2022 How to call a constructor from another constructor within the same class (not from subclass)
Mar 14, 2022 Role of superclass constructors in an object’s life
Mar 02, 2022 MOOC.fi Java Programming I Part 11
Feb 26, 2022 MOOC.fi Java Programming I Part 10
Feb 21, 2022 Constructor
Feb 19, 2022 MOOC.fi Java Programming I Part 9
Feb 16, 2022 Invoking the superclass version of a method
Feb 14, 2022 How to differentiate class, a subclass, an abstract class or an interface?
Feb 13, 2022 MOOC.fi Java Programming I Part 8
Feb 10, 2022 Interface
Feb 08, 2022 MOOC.fi Java Programming I Part 7
Feb 07, 2022 Casting Polymorphism
Feb 03, 2022 Object Class polymorphism
Feb 03, 2022 MOOC.fi Java Programming I Part 6
Jan 27, 2022 Deeper knowledge on Polymorphism
Jan 27, 2022 MOOC.fi Java Programming I Part 5
Jan 24, 2022 Polymorphism
Jan 21, 2022 Inheritance
Jan 20, 2022 MOOC.fi Java Programming I Part 4
Jan 19, 2022 Encapsulation in Java
Jan 17, 2022 Difference between local and instance variables
Jan 14, 2022 Short-Circuit Operators ( && , || ) vs Non-Short-Circuit Operators ( &, | )
Jan 14, 2022 MOOC.fi Java Programming I Part 3
Jan 10, 2022 MOOC.fi Java Programming I Part 2
Jan 05, 2022 MOOC.fi Java Programming I Part 1

Linux

Jun 14, 2023 How to set JDK in bash profile in linux
May 24, 2023 How to set environment variable in bash profile in linux
Dec 01, 2022 Linux ln -s (Symbolic link)

MOOC.fi

Mar 02, 2022 MOOC.fi Java Programming I Part 11
Feb 26, 2022 MOOC.fi Java Programming I Part 10
Feb 19, 2022 MOOC.fi Java Programming I Part 9
Feb 13, 2022 MOOC.fi Java Programming I Part 8
Feb 08, 2022 MOOC.fi Java Programming I Part 7
Feb 03, 2022 MOOC.fi Java Programming I Part 6
Jan 27, 2022 MOOC.fi Java Programming I Part 5
Jan 20, 2022 MOOC.fi Java Programming I Part 4
Jan 14, 2022 MOOC.fi Java Programming I Part 3
Jan 10, 2022 MOOC.fi Java Programming I Part 2
Jan 05, 2022 MOOC.fi Java Programming I Part 1

Markdown

Nginx

Sep 21, 2022 Nginx Basic commands

Python

Mar 22, 2023 Using helper functions in python and updating return value
Mar 20, 2023 List index out of range (list initialised wrong!)
Mar 14, 2023 List as method argument and parameter in Python
Mar 12, 2023 Appending return value to list in Python
Mar 08, 2023 Appending list to list in Python will not work

Querydsl

Jun 16, 2023 Limitations of subquery in Querydsl
Jun 12, 2023 ExpressionUtils.sum() not allowed in querydsl
Jun 08, 2023 error no property "some_method_name" not found for type "entity"
Jun 01, 2023 OracleDatabaseException table or view does not exist error when generate-ddl is set to none
May 22, 2023 BooleanExpression in Querydsl and use booleanexpression over booleanbuilder
Mar 08, 2023 When should your repoImpl extend Querydsl querydslrepositorysupport?
Mar 06, 2023 Querydsl noSuchMethodException
Mar 03, 2023 insert number does not match select in Querydsl JPA
Mar 01, 2023 How to set up Querydsl in your Spring Boot gradle project

Redis

Oct 14, 2022 Authorisation with Redis

Sliding window

Dec 23, 2022 Sliding window

Spring

May 17, 2023 Spring Legacy and some precautions
May 03, 2023 ThreadLocal to change Hibernate's query manually
Mar 31, 2023 What if we don't add @Column annotation to our fields? How are they mapped then?
Mar 29, 2023 Declaring role in SecurityFilterChain (I struggled with this a lot)
Mar 17, 2023 Convert dto to entity and vice versa with MapStruct
Feb 27, 2023 Error - no ParameterResolver registered for parameter error
Feb 24, 2023 Mockito
Feb 22, 2023 NullPointer with Spring Security's loadUserByUsername
Feb 20, 2023 Careful with Spring Security's SecurityFilterChain (front slash for url!)
Feb 15, 2023 Error Neither BindingResult nor plain target object for bean name '...' available as request attribute
Feb 13, 2023 Spring Security's default Login page feature
Feb 10, 2023 Error - preparing SQL statement
Feb 08, 2023 Set up directories in your Spring project properly
Feb 02, 2023 How to cleanly convert Dtos to Entities and vice versa
Jan 03, 2023 How to change and run different configurations in multi-module Spring project?
Dec 01, 2022 Spring ConstraintViolationException error solution
Nov 26, 2022 Protected annotation
Nov 12, 2022 What is DTO and its difference between VO?
Nov 02, 2022 How to handle entity inside DTO?
Oct 25, 2022 What is Dependency Injection and how to do it via constructor?
Oct 17, 2022 Difference between Spring filter and interceptor?
Oct 17, 2022 Spring Events and what are they?
Oct 02, 2022 Error with ModelMapper and solution - Parameter 1 of constructor in Service class required a bean of type 'org.modelmapper.ModelMapper' that could not be found.
Sep 26, 2022 Basic JPA annotations you should know (e.g. PersistenceContext, Transactional, etc)
Sep 21, 2022 Error-BeanCreationException at AbstractAutowireCapableBeanFactory
Sep 20, 2022 Can we have 2 Lombok's @Builder in 1 class?
Sep 19, 2022 JPA repository.save is Null (NullPointerException) - feat. @RunWith & @SpringBootTest & @DataJpaTest
Sep 14, 2022 NEVER put LocalDateTime into DTOs!
Sep 08, 2022 Difference between NotBlank, NotEmpty and NotNull when validating DTOs
Sep 04, 2022 Spring MVC Basic Knowledge
Sep 01, 2022 How does Spring MVC work?
Aug 16, 2022 How to manage DTOs in Spring Boot well
Aug 10, 2022 Spring Multi-module structure
Aug 07, 2022 What is Lombok's Builder and why do we use it?
Aug 02, 2022 Spring JAR vs WAR
Jul 17, 2022 Difference between ModelAttribute and Model annotations
Jul 17, 2022 IntelliJ Shortcut Windows
Jul 04, 2022 Good Spring practice to follow
Jun 20, 2022 Controller VS RestController
Jun 05, 2022 Logging with Lombok's @Slf4j
Jun 01, 2022 Spring Controller and difference between Controller VS RestController
May 23, 2022 yml file for setting up local, dev, production environment
Apr 29, 2022 Make good CRUD APIs (feat. DTO)
Apr 27, 2022 JsonIgnore annotation
Apr 25, 2022 How to create effective APIs with DTO?
Apr 19, 2022 Prevent multiple ways to initialise/create Object
Mar 11, 2022 When to add business logic to domain class, not service
Mar 09, 2022 How to test exception in test cases
Mar 03, 2022 Enumerated annotation and its EnumType types
Mar 01, 2022 PathVariable annotation
Feb 25, 2022 Tips on application.yml
Feb 23, 2022 Command Query Separation
Feb 08, 2022 Spring Devtools

Spring Security

Mar 29, 2023 Declaring role in SecurityFilterChain (I struggled with this a lot)
Feb 22, 2023 NullPointer with Spring Security's loadUserByUsername
Feb 20, 2023 Careful with Spring Security's SecurityFilterChain (front slash for url!)
Feb 13, 2023 Spring Security's default Login page feature

Stack

Jul 06, 2023 Programmers 기능개발
Jul 05, 2023 Programmers 같은 숫자는 싫어

Thymeleaf

Feb 17, 2023 Comparing 2 strings in thymeleaf
Nov 03, 2022 Classappend and No-operation (_) in Thymeleaf
Nov 01, 2022 Safe Navigation Operator (?) in Thymeleaf to prevent NullPointerException

application.yml

Dec 28, 2022 application.yml for Multi-Module (feat. AWS RDS settings)
Oct 30, 2022 Could not resolve placeholder 'test.name' in value "${test.name}"
Sep 23, 2022 H2 db connection with application.yml