• Introduction
• Part 1 Good Code
  • Chapter 1 Safety
  • 引言
  • 第1条：限制可变性
  • 第2条：最小化变量作用域
  • 第3条：尽快消除平台类型
  • 第4条：不要把推断类型暴露给外部
  • Item 5 Specify Your Expectations On Arguments And State
  • 第6条：尽可能使用标准库中提供的异常
  • 第7条：当不能返回预期结果时，优先使用null o或Failure 作为返回值
  • Item 8 Handle Nulls Properly
  • 第9条：使用use关闭资源
  • Item 10 Write Unit Tests
  • Chapter 2 Readability
  • Introduction
  • Item 11 Design For Readability
  • Item 12 Operator Meaning Should Be Consistent With Its Function Name
  • Item 13 Avoid Returning Or Operating On Unit
  • Item 14 Specify The Variable Type When It Is Not Clear
  • Item 15 Consider Referencing Receivers Explicitly
  • Item 16 Properties Should Represent State Not Behavior
  • Item 17 Consider Naming Arguments
  • Item 18 Respect Coding Conventions
• Part 2 Code Design
  • Chapter 3 Reusability
  • Introduction
  • Item 19 Do Not Repeat Knowledge
  • Item 20 Do Not Repeat Common Algorithms
  • Item 21 Use Property Delegation To Extract Common Property Patterns
  • Item 22 Use Generics When Implementing Common Algorithms
  • Item 23 Avoid Shadowing Type Parameters
  • Item 24 Consider Variance For Generic Types
  • Item 25 Reuse Between Different Platforms By Extracting Common Modules
  • Chapter 4 Abstraction Design
  • Introduction
  • Item 26 Each Function Should Be Written In Terms Of A Single Level Of Abstraction
  • Item 27 Use Abstraction To Protect Code Against Changes
  • Item 28 Specify API Stability
  • Item 29 Consider Wrapping External API
  • Item 30 Minimize Elements Visibility
  • Item 31 Define Contract With Documentation
  • Item 32 Respect Abstraction Contracts
  • Chapter 5 Object Creation
  • Introduction
  • Item 33 Consider Factory Functions Instead Of Constructors
  • Item 34 Consider A Primary Constructor With Named Optional Arguments
  • Item 35 Consider Defining A DSL For Complex Object Creation
  • Chapter 6 Class Design
  • Introduction
  • Item 36 Prefer Composition Over Inheritance
  • Item 37 Use The Data Modifier To Represent A Bundle Of Data
  • Item 38 Use Function Types Instead Of Interfaces To Pass Operations And Actions
  • Item 39 Prefer Class Hierarchies To Tagged Classes
  • Item 40 Respect The Contract Of Equals
  • Item 41 Respect The Contract Of Hash Code
  • Item 42 Respect The Contract Of Compare To
  • Item 43 Consider Extracting Non Essential Parts Of Your API Into Extensions
  • Item 44 Avoid Member Extensions
• Part 3 Efficiency
  • Chapter 7 Make It Cheap
  • Introduction
  • Item 45 Avoid Unnecessary Object Creation
  • Item 46 Use Inline Modifier For Functions With Parameters Of Functional Types
  • Item 47 Consider Using Inline Classes
  • Item 48 Eliminate Obsolete Object References
  • Chapter 8 Efficient Collection Processing
  • Introduction
  • Item 49 Prefer Sequence For Big Collections With More Than One Processing Step
  • Item 50 Limit The Number Of Operations
  • Item 51 Consider Arrays With Primitives For Performance Critical Processing
  • Item 52 Consider Using Mutable Collections
• Published with GitBook

Introduction

Chapter 5: Object creation

Although Kotlin can be written in a purely functional style, it can also be written in object oriented programming (OOP), much like Java. In OOP, we need to create every object we use, or at least define how it ought to be created, and different ways have different characteristics. It is important to know what options do we have. This is why this chapter shows different ways how we can define object creation, and explains their advantages and disadvantages.

If you are familiar with the Effective Java book by Joshua Bloch, then you may notice some similarities between this chapter and that book. It is no coincidence. This chapter relates to the first chapter of Effective Java. Although Kotlin is very different from Java, and there are only morsels of knowledge that can be used. For instance, static methods are not allowed in Kotlin, but we have very good alternatives like top-level functions and companion object functions. They don’t work the same way as static functions, so it is important to understand them. Similarly, with other items, you can notice similarities, but the changes that Kotlin has introduced are important. To cheer you up: these changes are mostly to provide more possibilities or force better style. Kotlin is a powerful and really well-designed language, and this chapter should mainly open your eyes to these new possibilities.

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