Kotlin相比Java的新特性

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Kotlin和Java都属于JVM系的语言，这意味着Kotlin和Java代码，最后都会编译为字节码文件，因此，两者在一些核心概念上没有太大区别，Kotlin可以看作是Java的改进版本，这里只讨论一些Kotlin特有的特性。

📝 区别点

扩展函数

高级函数

挂起函数

协程

flow

委托

空指针安全

协变、逆变

扩展函数

Extension functions allow you to add new functions to existing classes without modifying their source code.

Demo:

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Extension functions are resolved statically at compile-time based on the type of the variable they are invoked on. They are not part of the class themselves.

高级函数

Higher-order functions are functions that take functions as parameters or return a function.

Demo:

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Kotlin functions are first-class citizens, meaning they can be stored in variables, passed as arguments, or returned from other functions.

挂起函数

Suspend functions are special functions in Kotlin that can be paused and resumed during execution. It is modified by suspend.

Demo:

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Suspend functions are transformed by the Kotlin compiler into a state machine where the states represent suspension points.

协程

Coroutines are a concurrency design pattern that you can use in Kotlin to simplify asynchronous programming by writing code in a sequential manner.

Demo:

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Implemented via state machines and continuation-passing style programming, coroutines in Kotlin are built on top of the Java threading model but use fewer resources and scale better.

Flow

Flow is a type in Kotlin that represents a cold asynchronous stream of data that sequentially emits values and completes normally or with an exception.

Demo:

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Flow builds upon coroutines and channels, providing a rich API for composing asynchronous logic.

委托

Delegation is a design pattern where an object delegates part of its responsibilities to another object. In Kotlin, delegation can be used both for properties (property delegation) and for implementing interfaces (class delegation).

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Kotlin implements delegation by automatically forwarding calls to the delegated object.

空指针安全

Kotlin's type system is designed to eliminate the danger of null references from code, also known as the "billion-dollar mistake.”

Demo:

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Kotlin's type system distinguishes between nullable and non-nullable types, and it enforces null checks at compile time.

协变与逆变

In Kotlin, covariance and contravariance are used to flexibly handle subtype relationships between generic types, enabling more complex and flexible hierarchies.

协变:

逆变：

📎 说明

文章相关的使用例子，由GPT4协助生成，GPT确实是效率神器