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    • Jenkins μ‹œμž‘ν•˜κΈ°
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  • 개발 방법둠
    • TDD
  • Spring
    • IoC
    • Is Spring Bean Thread-Safe?
    • Spring Singleton
    • Component Scan
    • Spring Annotation
    • 의쑴 관계 μ£Όμž…(DI)
    • Lombok ν™œμš©ν•˜κΈ°
    • Bean 생λͺ…주기와 콜백
    • Bean Scope
    • AOP(1) - AOPλž€
    • AOP(2) - Aop Proxy
    • AOP(3) - Dynamic Proxy
    • AOP(4) - AspectJ
    • POJO
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    • Transaction
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    • JPA Entity
    • Spring Data JPA
    • Spring Data Specification
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    • Cache
    • restTemplate
    • YAML 파일 μ„€μ •
    • Spring Boot
      • H2 DB μ„€μ •
      • 닀쀑 λ°μ΄ν„°λ² μ΄μŠ€ μ„€μ •
      • Mybatis μ—°λ™ν•˜κΈ°
    • Spring Batch
      • Batch μ‹œμž‘ν•΄λ³΄κΈ°
      • Batch Job Flow
      • Job
      • Step
      • Batch Scope & Job Parameter
      • JobRepository와 λ©”νƒ€ν…Œμ΄λΈ”
      • Chunk μ§€ν–₯ ν”„λ‘œκ·Έλž˜λ°
      • ItemReader
      • ItemProcessor
      • ItemWriter
      • Batch Schedular
      • Job별 Beanλ“±λ‘ν•˜κΈ°
      • Batch κ΅¬ν˜„μ‹œ λ°œμƒν•œ 였λ₯˜ 정리
      • Spring Batch Scaling
        • Multithread Jobκ΅¬ν˜„μ‹œ μ΄μŠˆμ‚¬ν•­
    • Spring test
      • Junit5
        • ν…ŒμŠ€νŠΈ 이름 ν‘œκΈ°
        • ν…ŒμŠ€νŠΈ κ·Έλ£Ή μ‚¬μ΄μ˜ 관계
        • νƒœκ·Έμ™€ 필터링
        • 동적 ν…ŒμŠ€νŠΈ
        • ν…ŒμŠ€νŠΈ LifeCycle
        • ν…ŒμŠ€νŠΈ λ©”μ„œλ“œ
        • ν…ŒμŠ€νŠΈ μˆœμ„œ
        • AssertJ
        • ν…ŒμŠ€νŠΈ 병렬 μ‹€ν–‰
        • AssertJ
        • Mock
      • Spring Boot Test DB 뢄리
      • Spring Batch Test
  • Web Application
    • Web Server & WAS
    • κ΄€λ ¨ κ°œλ… - HTTP API, HTML, CSR, SSR
    • Servlet
    • JSP
    • Cookie And Session
    • μ˜ˆμ™ΈνŽ˜μ΄μ§€
    • Java Bean
    • JDBC
    • Connection Pool
    • 파일 μ—…λ‘œλ“œ
    • Expression Language
    • JSTL
    • FrontControllerνŒ¨ν„΄ Command νŒ¨ν„΄
    • Forwarding
    • MVC
    • νšŒμ›κ°€μž…μ˜ˆμ œ
    • μ°Έκ³ 
      • κ°œλ°œν™˜κ²½μ„€μ •
  • Java+
    • SOAP/WSDL vs REST
    • WSDL을 JAVA둜 λ³€ν™˜ν•˜κΈ°
    • SOAP 톡신 OPEN API둜 κ°œλ°œν•΄λ³΄κΈ°
  • Java
    • Basic
      • λ³€μˆ˜μ™€ νƒ€μž…
      • μ—°μ‚°μž
      • 쑰건문과 반볡문
      • μ°Έμ‘° νƒ€μž…
      • 클래슀
      • 상속(Inheritance)
      • μΈν„°νŽ˜μ΄μŠ€(Interface)
      • 쀑첩 ν΄λž˜μŠ€μ™€ 쀑첩 μΈν„°νŽ˜μ΄μŠ€
      • μ˜ˆμ™Έ 처리
      • API - Object, System, Class, Math, Wrapper
      • API - String, StringBuffer, StringBuilder
      • Thread
      • Generic
      • Lambda
      • Collection - List, Set
      • Collection - Map
      • Collection - Tree
      • Collection - Stack, Queue
      • Stream
      • Reflection
      • μ •κ·œν‘œν˜„μ‹
      • GUI
      • UML
      • Serializable
    • Advanced
      • OutOfMemoryError
      • AutoValue
      • meta-annotation
        • @Retention
        • @Target
        • @Repeatable
    • Effective Java 3/E
      • ITEM 1: Static Factory Method(정적 λ©”μ†Œλ“œ)
      • ITEM 2: Builder Pattern
      • ITEM 3: Singleton
      • ITEM 4: Private Constructor
      • ITEM 5: Dependency Injection
      • ITEM 6: Avoid Unnecessary Object
      • ITEM 7: Eliminate Object Reference
      • ITEM 8: Avoid finalizer and cleaner
      • ITEM 9: try-with-resources
      • ITEM 10: The gerneral contract when overriding equlas
      • ITEM 11: Overriding hashCode
      • ITEM 12: overriding toString
      • ITEM 13: overriding clone judiciously
      • ITEM 14: Consider implementing comparable
      • ITEM 15: ν΄λž˜μŠ€μ™€ λ©€λ²„μ˜ 접근을 μ΅œμ†Œν™”ν•΄λΌ
      • ITEM 16: Use Accessor methods
      • ITEM 17: λ³€κ²½ κ°€λŠ₯성을 μ΅œμ†Œν™”ν•΄λΌ(λΆˆλ³€ 클래슀)
      • ITEM 18: 상속보단 μ»΄ν¬μ§€μ…˜μ„ μ‚¬μš©ν•΄λΌ
      • ITEM 19: 상속을 κ³ λ €ν•΄ μ„€κ³„ν•˜κ³  λ¬Έμ„œν™”ν•΄λΌ
      • ITEM 20: 좔상 ν΄λž˜μŠ€λ³΄λ‹€ μΈν„°νŽ˜μ΄μŠ€λ₯Ό μš°μ„ ν•˜λΌ
      • ITEM 21: μΈν„°νŽ˜μ΄μŠ€λŠ” κ΅¬ν˜„ν•˜λŠ” μͺ½μ„ 생각해 섀계해라.
      • ITEM 22: μΈν„°νŽ˜μ΄μŠ€λŠ” νƒ€μž…μ„ μ •μ˜ν•˜λŠ” μš©λ„λ‘œλ§Œ μ‚¬μš©ν•΄λΌ
      • ITEM 23: νƒœκ·Έ 달린 ν΄λž˜μŠ€λ³΄λ‹€ 클래슀 계측ꡬ쑰λ₯Ό ν™œμš©ν•΄λΌ
      • ITEM 24: 멀버 ν΄λž˜μŠ€λŠ” λ˜λ„λ‘ static으둜 κ΅¬ν˜„ν•΄λΌ
      • ITEM 25: ν†±λ ˆλ²¨ ν΄λž˜μŠ€λŠ” ν•œ νŒŒμΌμ— ν•˜λ‚˜λ§Œ 생성해라.
      • ITEM 26: Raw type은 μ‚¬μš©ν•˜μ§€ 마라
      • ITEM 27: 비검사 κ²½κ³ λ₯Ό μ œκ±°ν•΄λΌ
      • ITEM 28: λ°°μ—΄λ³΄λ‹€λŠ” 리슀트λ₯Ό μ‚¬μš©ν•΄λΌ
      • ITEM 29: 이왕이면 μ œλ„€λ¦­ νƒ€μž…μœΌλ‘œ λ§Œλ“€μ–΄λΌ
      • ITEM 30: 이왕이면 μ œλ„€λ¦­ λ©”μ„œλ“œλ‘œ λ§Œλ“€μ–΄λΌ
      • ITEM 31 : ν•œμ •μ  μ™€μΌλ“œμΉ΄λ“œλ₯Ό μ‚¬μš©ν•΄ API μœ μ—°μ„±μ„ 높여라
      • ITEM 32: μ œλ„€λ¦­κ³Ό κ°€λ³€μΈμˆ˜λ₯Ό ν•¨κ»˜ μ“Έ λ•ŒλŠ” 신쀑해라
      • ITEM 33: νƒ€μž… μ•ˆμ „ 이쒅 μ»¨ν…Œμ΄λ„ˆλ₯Ό 고렀해라
      • ITEM 34: int μƒμˆ˜ λŒ€μ‹  μ—΄κ±° νƒ€μž…μ„ μ‚¬μš©ν•΄λΌ
      • ITEM 35: ordinal λ©”μ„œλ“œ λŒ€μ‹  μΈμŠ€ν„΄μŠ€ ν•„λ“œλ₯Ό μ‚¬μš©ν•΄λΌ
      • ITEM 36: λΉ„νŠΈ ν•„λ“œ λŒ€μ‹  EnumSet을 μ‚¬μš©ν•΄λΌ
      • ITEM 37: ordinal 인덱싱 λŒ€μ‹  EnumMap을 μ‚¬μš©ν•΄λΌ
      • TEM 38 : ν™•μž₯ν•  수 μžˆλŠ” μ—΄κ±°νƒ€μž…μ΄ ν•„μš”ν•˜λ©΄ μΈν„°νŽ˜μ΄μŠ€λ₯Ό μ‚¬μš©ν•΄λΌ
      • ITEM 39: λͺ…λͺ… νŒ¨ν„΄λ³΄λ‹€ μ• λ„ˆν…Œμ΄μ…˜μ„ μ‚¬μš©ν•΄λΌ
      • ITEM 40: @Override μ–΄λ…Έν…Œμ΄μ…˜μ„ μΌκ΄€λ˜κ²Œ μ‚¬μš©ν•΄λΌ
      • ITEM 41: μ •μ˜ν•˜λ €λŠ” 것이 νƒ€μž…μ΄λΌλ©΄ 마컀 μΈν„°νŽ˜μ΄μŠ€λ₯Ό μ‚¬μš©ν•΄λΌ
      • ITEM 42: 읡λͺ… ν΄λž˜μŠ€λ³΄λ‹€λŠ” λžŒλ‹€λ₯Ό μ‚¬μš©ν•΄λΌ
      • ITEM 43: λžŒλ‹€λ³΄λ‹€λŠ” λ©”μ„œλ“œ μ°Έμ‘°λ₯Ό μ‚¬μš©ν•΄λΌ
      • ITEM 44: ν‘œμ€€ ν•¨μˆ˜ν˜• μΈν„°νŽ˜μ΄μŠ€λ₯Ό μ‚¬μš©ν•΄λΌ
      • ITEM 45: μŠ€νŠΈλ¦Όμ€ μ£Όμ˜ν•΄μ„œ μ‚¬μš©ν•΄λΌ
      • ITEM 46: μŠ€νŠΈλ¦Όμ—μ„œ λΆ€μž‘μš© μ—†λŠ” ν•¨μˆ˜λ₯Ό μ‚¬μš©ν•΄λΌ
      • ITEM 47: λ°˜ν™˜ νƒ€μž…μœΌλ‘œλŠ” μŠ€νŠΈλ¦Όλ³΄λ‹€ μ»¬λ ‰μ…˜μ΄ λ‚«λ‹€.
      • ITEM 48: 슀트림 λ³‘λ ¬ν™”λŠ” μ£Όμ˜ν•΄μ„œ μ‚¬μš©ν•΄λΌ
      • ITEM 49: λ§€κ°œλ³€μˆ˜κ°€ μœ νš¨ν•œμ§€ 검사해라
      • ITEM 50: μ μ‹œμ— 방어적 볡사본을 λ§Œλ“€μ–΄λΌ
      • ITEM 51: λ©”μ„œλ“œ μ‹œκ·Έλ‹ˆμ²˜λ₯Ό μ‹ μ€‘νžˆ 섀계해라
      • ITEM 52: λ‹€μ€‘μ •μ˜λŠ” μ‹ μ€‘νžˆ μ‚¬μš©ν•΄λΌ
      • ITEM 53: κ°€λ³€μΈμˆ˜λŠ” μ‹ μ€‘νžˆ μ‚¬μš©ν•΄λΌ
      • ITEM 54: null이 μ•„λ‹Œ, 빈 μ»¬λ ‰μ…˜μ΄λ‚˜ 배열을 λ°˜ν™˜ν•΄λΌ
      • ITEM 55: Optional λ°˜ν™˜μ€ μ‹ μ€‘ν•˜κ²Œ 해라
      • ITEM 56: 곡개된 API μš”μ†Œμ—λŠ” 항상 주석을 μž‘μ„±ν•΄λΌ
      • ITEM 57: μ§€μ—­λ³€μˆ˜μ˜ λ²”μœ„λ₯Ό μ΅œμ†Œν™”ν•΄λΌ
      • ITEM 58: 전톡적인 for λ¬Έλ³΄λ‹€λŠ” for-each문을 μ‚¬μš©ν•΄λΌ
      • ITEM 59: 라이브러리λ₯Ό 읡히고 μ‚¬μš©ν•΄λΌ
      • ITEM 60: μ •ν™•ν•œ 닡이 ν•„μš”ν•˜λ‹€λ©΄ float와 double은 피해라
      • ITEM 61: λ°•μ‹±λœ κΈ°λ³Έ νƒ€μž…λ³΄λ‹€λŠ” κΈ°λ³Έ νƒ€μž…μ„ μ‚¬μš©ν•΄λΌ
      • ITEM 62: λ‹€λ₯Έ νƒ€μž…μ΄ μ μ ˆν•˜λ‹€λ©΄ λ¬Έμžμ—΄ μ‚¬μš©μ„ 피해라
      • ITEM 63: λ¬Έμžμ—΄ 연결은 λŠλ¦¬λ‹ˆ μ£Όμ˜ν•΄λΌ
      • ITEM 64: κ°μ²΄λŠ” μΈν„°νŽ˜μ΄μŠ€λ₯Ό μ‚¬μš©ν•΄ 참쑰해라
      • ITEM 65: λ¦¬ν”Œλ ‰μ…˜λ³΄λ‹€λŠ” μΈν„°νŽ˜μ΄μŠ€λ₯Ό μ‚¬μš©ν•΄λΌ
      • ITEM 66: λ„€μ΄ν‹°λΈŒ λ©”μ„œλ“œλŠ” μ‹ μ€‘νžˆ μ‚¬μš©ν•΄λΌ
      • ITEM 67: μ΅œμ ν™”λŠ” μ‹ μ€‘νžˆ 해라
      • ITEM 68: 일반적으둜 ν†΅μš©λ˜λŠ” λͺ…λͺ… κ·œμΉ™μ„ 따라라
    • 객체지ν–₯ 섀계 원칙(SOLID)
    • λ””μžμΈνŒ¨ν„΄
      • Strategy Pattern
      • Template Method Pattern
      • Factory Method Pattern
      • Singleton
      • Delegation
      • Proxy
      • Adapter Pattern
    • μ‹€μŠ΅
      • μΈν„°νŽ˜μ΄μŠ€ μ‹€μŠ΅ - Vehicle
      • μΈν„°νŽ˜μ΄μŠ€ μ‹€μŠ΅ - Remote
      • GUI μ‹€μŠ΅ - Calculator
      • GUI μ‹€μŠ΅ - button
      • GUI μ‹€μŠ΅ - lotto
      • Thread μ‹€μŠ΅ - μ’Œμ„μ˜ˆμ•½, 메세지보내기
    • Jar vs War
  • λ°μ΄ν„°λ² μ΄μŠ€
    • KEY
    • Index
    • Transaction
    • Trigger
    • Procedure / Function
    • Package
    • λ°μ΄ν„°λ² μ΄μŠ€ 배움터
      • λ°μ΄ν„°λ² μ΄μŠ€ μ‹œμŠ€ν…œ
      • 관계데이터 λͺ¨λΈ
      • κ΄€κ³„λŒ€μˆ˜μ™€ SQL
    • MySQL
      • Databaseλž€
      • MySQL μ‹œμž‘ν•˜κΈ°
      • MySQL Database
      • MySQL Table
      • CRUD
      • κ΄€κ³„ν˜• λ°μ΄ν„°λ² μ΄μŠ€
      • Server와 Client
    • PostgreSQL
    • NoSQL
      • Install Cassandra on mac
      • Cassandraλž€?
      • NiFiλž€
  • Algorithm
    • String
    • Recursion
    • Dynamic Programming
    • Array, Struct, Pointer
    • Math
    • Sort
    • List
    • Stack
    • Queue
    • Graph
    • Tree
    • Maze
    • AVL
    • μ΄μ§„νƒμƒ‰νŠΈλ¦¬(Binary Search Tree)
    • DFS와 BFS
    • λ‹€μ΅μŠ€νŠΈλΌ μ•Œκ³ λ¦¬μ¦˜(Dijkstra's Algorithm)
    • Red-Black 트리
    • A* μ•Œκ³ λ¦¬μ¦˜
    • Heap
    • Huffman Coding
    • Priority Queue
    • Bellman-Ford μ•Œκ³ λ¦¬μ¦˜
    • C++
      • Class
      • STL
        • STL pair
        • STL Container - Associate Container
        • STL Container - Sequence Container
        • STL Container - Container Adapter
  • JavaScript
    • JABASCRIPT BASIC
    • Shallow Copy vs Deep Copy
    • OBJECT MODEL
    • NODE
    • 동기 처리 vs 비동기 처리
    • AJAX
    • CALLBACK
    • PROMISE
    • DEFERRER
    • UNDERSCORE
    • WEBPACK
    • SCOPE
    • EXECUTION CONTEXT
    • Image Object
    • BFCacheλž€?
    • history.scrollRestoration
    • Intersection Observer
    • JWT - JSON Web Token
    • HTML vs JSON
  • Vue.js
    • ν™˜κ²½μ„€μ •
    • Vue.jsλž€?
    • Vue Instance
    • Vue Component
    • Vue Router
    • HTTP 톡신
    • Template
    • Single File Component
    • Vue Animation
    • Vuex
    • Djnago와 μ—°λ™ν•˜κΈ°
  • Backbone.js
    • Model
    • Collection
    • Sync
    • view
  • Node.js
    • Doit! - λ…Έλ“œλ‘œ λ§Œλ“€ 수 μžˆλŠ” λŒ€ν‘œμ μΈ μ„œλ²„μ™€ μš©λ„
    • Doit! - λ…Έλ“œμ— λŒ€ν•΄ μ•Œμ•„λ³΄κ³  개발 도ꡬ μ„€μΉ˜ν•˜κΈ°
    • Doit! - λ…Έλ“œ κ°„λ‹¨ν•˜κ²Œ μ‚΄νŽ΄λ³΄κΈ°
    • Doit! - λ…Έλ“œμ˜ μžλ°”μŠ€ν¬λ¦½νŠΈμ™€ μΉœν•΄μ§€κΈ°
    • Doit! - λ…Έλ“œμ˜ κΈ°λ³Έ κΈ°λŠ₯ μ•Œμ•„λ³΄κΈ°
    • Doit! - μ›Ή μ„œλ²„ λ§Œλ“€κΈ°
    • Doit! - λ°μ΄ν„°λ² μ΄μŠ€ μ‚¬μš©ν•˜κΈ°
    • Doit! - μ΅μŠ€ν”„λ ˆμŠ€ ν”„λ‘œμ νŠΈλ₯Ό λͺ¨λ“ˆν™”ν•˜κΈ°
    • Doit! - λ·° ν…œν”Œλ¦Ώ μ μš©ν•˜κΈ°
    • Doit! - 패슀포트둜 μ‚¬μš©μž μΈμ¦ν•˜κΈ°
    • Doit! - μ±„νŒ…μ„œλ²„ λ§Œλ“€κΈ°
    • Doit! - JSON-RPC μ„œλ²„ λ§Œλ“€κΈ°
  • Python
    • Warning-Could not import the lzma module
    • Pandas
      • Pandas 자료ꡬ쑰
      • Pandas 데이터 μž…μΆœλ ₯
      • DataFrame Data μ‚΄νŽ΄λ³΄κΈ°
      • μ‹œκ°ν™” 도ꡬ - Matplotlib
  • ML
    • μΆ”μ²œ μ‹œμŠ€ν…œ
      • Collaborative Filtering
      • Matrix Factorization
  • Django
    • Basic
      • ν™˜κ²½μ„€μ •
      • About Django
      • Start Django Project
      • Secret Key κ΄€λ¦¬ν•˜κΈ°
      • Settings λΆ„λ¦¬ν•˜κΈ°
      • Django App
      • Django View & URL (1)
      • Django Model
        • MySQL 연동
      • Django Admin
      • Django View & URL (2)
      • Django Template
      • Django Template & View & URL
      • Django Static
      • Django form
    • Advanced
      • Django Generic View
      • Django Automated Testing
      • Django Extenstion Template
      • Django Model Package
      • Django OpenSSL setting
    • REST framework
      • Rest API
      • Serializers
      • ViewSet
    • Error
      • ν™˜κ²½μ„€μ • zlib 였λ₯˜λ°œμƒ
      • ModuleNotFoundError
    • νŒ¨ν‚€μ§€
      • django-debug-toolbar
    • Vue.js μ—°λ™ν•˜κΈ°
  • Ruby
    • variable & input/output
    • 쑰건문
    • 반볡문
    • Array & Hash
    • Method
    • Proc&Lamda
    • Class
  • Ruby on Rails
    • Scaffolding
    • Controller
    • Model
    • Model-M:N relation
    • Model Validation
    • 멋사 10μ£Όμ°¨ μˆ˜μ—…(Tip)
  • HTML/CSS
    • Udacity - Intro to HTML/CSS
    • Udacity - Responsive Web Design
    • Udacity - Responsive Images
    • HTML Basic
    • CSS Basic
    • HTML5 Sementic Tag
    • HTML ν…μŠ€νŠΈ κ΄€λ ¨ νƒœκ·Έλ“€
    • HTML5 λ©€ν‹°λ―Έλ””μ–΄
    • HTML 폼 κ΄€λ ¨ νƒœκ·Έλ“€
    • ν…μŠ€νŠΈ κ΄€λ ¨ μŠ€νƒ€μΌ
    • 색상과 배경을 μœ„ν•œ μŠ€νƒ€μΌ
    • λ ˆμ΄μ•„μ›ƒμ„ μœ„ν•œ μŠ€νƒ€μΌ
    • CSS 포지셔닝
    • λ‹€μž¬λ‹€λŠ₯ν•œ CSS3 μ„ νƒμž
    • CSS와 μ• λ‹ˆλ©”μ΄μ…˜
    • λ°˜μ‘ν˜• μ›Ήμ΄λž€?
  • OS(운영체제)
    • Linux
      • Daemon
      • Cron
      • ν”„λ‘œμ„ΈμŠ€ κ΄€λ ¨ λͺ…λ Ήμ–΄
      • ν…μŠ€νŠΈ 파일 λͺ…λ Ήμ–΄
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    • λ„€νŠΈμ›Œν¬ κΈ°λ³Έ κ°œλ…
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  • μ™œ 싱글톀을 μ‚¬μš©ν• κΉŒ?
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  1. Java
  2. λ””μžμΈνŒ¨ν„΄

Singleton

PreviousFactory Method PatternNextDelegation

Last updated 4 years ago

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μ• ν”Œλ¦¬μΌ€μ΄μ…˜μ΄ μ‹œμž‘λ  λ•Œ μ–΄λ–€ ν΄λž˜μŠ€κ°€ 졜초 ν•œλ²ˆλ§Œ λ©”λͺ¨λ¦¬λ₯Ό ν• λ‹Ήν•˜κ³ (static) κ·Έ λ©”λͺ¨λ¦¬μ— μΈμŠ€ν„΄μŠ€λ₯Ό λ§Œλ“€μ–΄ μ‚¬μš©ν•˜λŠ” λ””μžμΈ νŒ¨ν„΄μ΄λ‹€. μƒμ„±μžκ°€ μ—¬λŸ¬λ²ˆ ν˜ΈμΆœλ˜λ”λΌλ„ μ‹€μ œλ‘œ μƒμ„±λ˜λŠ” κ°μ²΄λŠ” ν•˜λ‚˜μ΄λ©°, 졜초 생성 이후 호좜된 μƒμ„±μžλŠ” μ΅œμ΄ˆμ— μƒμ„±ν•œ 객체λ₯Ό λ°˜ν™˜ν•œλ‹€.

즉, μΈμŠ€ν„΄μŠ€λ₯Ό ν•˜λ‚˜λ§Œ λ§Œλ“€μ–΄ μ‚¬μš©ν•˜κΈ°μœ„ν•œ νŒ¨ν„΄μ΄λ‹€.

ν•˜λ‚˜μ˜ μΈμŠ€ν„΄μŠ€λ§Œμ„ μƒμ„±ν•˜λŠ” μ±…μž„μ΄ 있으며, getInstance() λ©”μ„œλ“œλ₯Ό 톡해 λͺ¨λ“  ν΄λΌμ΄μ–ΈνŠΈμ—κ²Œ λ™μΌν•œ μΈμŠ€ν„΄μŠ€λ₯Ό λ°˜ν™˜ν•˜λŠ” μž‘μ—…μ„ μˆ˜ν–‰ν•œλ‹€.

public class Singleton {
    private static Singleton singletonObject;

    private Singleton() {}

    public static Singleton getInstance() {
        if (singletonObject == null) {
            singletonObject = new Singleton();
        }
        return singletonObject;
    }
}

ν•˜λ‚˜μ˜ μΈμŠ€ν„΄μŠ€λ§Œμ„ μœ μ§€ν•˜κΈ° μœ„ν•΄ μΈμŠ€ν„΄μŠ€ 생성에 νŠΉλ³„ν•œ μ œμ•½μ„ 걸어둬야 ν•œλ‹€. new λ₯Ό μ‹€ν–‰ν•  수 없도둝 μƒμ„±μžμ— private μ ‘κ·Ό μ œμ–΄μžλ₯Ό μ§€μ •ν•˜κ³ , μœ μΌν•œ 단일 객체λ₯Ό λ°˜ν™˜ν•  수 μžˆλ„λ‘ 정적 λ©”μ†Œλ“œλ₯Ό 지원해야 ν•œλ‹€. λ˜ν•œ μœ μΌν•œ 단일 객체λ₯Ό μ°Έμ‘°ν•  정적 μ°Έμ‘°λ³€μˆ˜κ°€ ν•„μš”ν•˜λ‹€.

문제점

λ©€ν‹°μŠ€λ ˆλ”© ν™˜κ²½μ—μ„œ μ‹±κΈ€ν„΄ νŒ¨ν„΄μ„ μ μš©ν•˜λ‹€λ³΄λ©΄ λ¬Έμ œκ°€ λ°œμƒν•  수 μžˆλ‹€. λ™μ‹œμ— μ ‘κ·Όν•˜λ‹€κ°€ ν•˜λ‚˜λ§Œ μƒμ„±λ˜μ–΄μ•Ό ν•˜λŠ” μΈμŠ€ν„΄μŠ€κ°€ 두 개 생성될 수 μžˆλŠ” 것이닀. μ΄λŸ¬ν•œ λ¬Έμ œλŠ” 1. μΈμŠ€ν„΄μŠ€λ₯Ό λ§Œλ“œλŠ” λ©”μ„œλ“œμ— λ™κΈ°ν™”ν•˜λŠ” 방법 (Thread-Safe Initialization) 2. 정적 λ³€μˆ˜μ— μΈμŠ€ν„΄μŠ€λ₯Ό λ§Œλ“€μ–΄ λ°”λ‘œ μ΄ˆκΈ°ν™”ν•˜λŠ” 방법 (Eager Initialization)으둜 ν•΄κ²°ν•  수 μžˆλ‹€.

public class Singleton {
    private static Singleton singletonObject;

    private Singleton() {}

    public static synchronized Singleton getInstance() {
        if (singletonObject == null) {
            singletonObject = new Singleton();
        }
        return singletonObject;
    }
}

λ‹¨μˆœνžˆ synchronized ν‚€μ›Œλ“œλ₯Ό μ‚¬μš©ν•˜λ©΄ μ„±λŠ₯상 μ΄μŠˆκ°€ μžˆμ„ 수 μžˆλ‹€.

public class Singleton {
    private static volatile Singleton singletonObject;

    private Singleton() {}

    public static Singleton getInstance() {
        if (singletonObject == null) {
            synchronized (Singleton.class) {
                if(singletonObject == null) {
                    singletonObject = new Singleton();
                }
            }
        }
        return singletonObject;
    }
}

λ‹€μŒκ³Ό 같이 DCL(Double Checking Locking)을 μ¨μ„œ getInstance()μ—μ„œ 동기화 λ˜λŠ” μ˜μ—­μ„ 쀄일 수 μžˆλ‹€. μ΄ˆκΈ°μ— 객체λ₯Ό μƒμ„±ν•˜μ§€ μ•ŠμœΌλ©΄μ„œλ„ λ™κΈ°ν™”ν•˜λŠ” 뢀뢄을 μž‘κ²Œ λ§Œλ“€μ—ˆλ‹€. κ·ΈλŸ¬λ‚˜ 이 μ½”λ“œλŠ” λ©€ν‹°μ½”μ–΄ ν™˜κ²½μ—μ„œ λ™μž‘ν•  λ•Œ, ν•˜λ‚˜μ˜ CPU λ₯Ό μ œμ™Έν•˜κ³ λŠ” λ‹€λ₯Έ CPU κ°€ lock 이 걸리게 λœλ‹€. κ·Έλ ‡κΈ° λ•Œλ¬Έμ— λ‹€λ₯Έ 방법이 ν•„μš”ν•˜λ‹€.

public class Singleton {
    private static volatile Singleton singletonObject = new Singleton();

    private Singleton() {}

    public static Singleton getSingletonObject() {
        return singletonObject;
    }
}

μ •μ λ³€μˆ˜μ— μΈμŠ€ν„΄μŠ€λ₯Ό λ§Œλ“€μ–΄ λ°”λ‘œ μ΄ˆκΈ°ν™” ν•˜λŠ” 방법(Eager initialization)으둜 ν•΄κ²°ν•  수 μžˆλ‹€.

μ™œ 싱글톀을 μ‚¬μš©ν• κΉŒ?

  1. κ³ μ •λœ λ©”λͺ¨λ¦¬ μ˜μ—­μ„ μ‚¬μš©ν•˜λ©΄μ„œ λ©”λͺ¨λ¦¬ λ‚­λΉ„λ₯Ό λ°©μ§€ν•  수 μžˆλ‹€.

  2. μ „μ—­ μΈμŠ€ν„΄μŠ€μ΄κΈ° λ•Œλ¬Έμ— λ‹€λ₯Έ 클래슀의 μΈμŠ€ν„΄μŠ€λ“€μ΄ 데이터λ₯Ό κ³΅μœ ν•˜κΈ° 쉽닀. (Connection Pool, μŠ€λ ˆλ“œ ν’€, λ””λ°”μ΄μŠ€ μ„€μ • 객체처럼 곡톡퇸 객체λ₯Ό μ—¬λŸ¬κ°œ 생성해 μ‚¬μš©ν•΄μ•Όν•˜λŠ” μƒν™©μ—μ„œ 많이 μ‚¬μš©)

  3. 두 번째 μ΄μš©μ‹œλΆ€ν„°λŠ” 객체 λ‘œλ”© μ‹œκ°„μ΄ 쀄어 μ„±λŠ₯이 μ’‹μ•„μ§„λ‹€.

μ°Έμ‘° νŽ˜μ΄μ§€

https://jeong-pro.tistory.com/86
https://asfirstalways.tistory.com/335
https://gmlwjd9405.github.io/2018/07/06/singleton-pattern.html
https://github.com/JaeYeopHan/Interview_Question_for_Beginner/tree/master/DesignPattern