第 6 章：类与对象

self、构造、继承；日常数据用 dataclass 最省事。

01最小类

Python

class User:
    def __init__(self, name: str):
        self.name = name

    def hello(self) -> str:
        return f"hi {self.name}"

u = User("Ada")
print(u.hello())

Kotlin

class User(val name: String) {
    fun hello() = "hi $name"
}
val u = User("Ada")
println(u.hello())

ArkTS

class User {
  name: string;
  constructor(name: string) {
    this.name = name;
  }
  hello(): string {
    return `hi ${this.name}`;
  }
}
const u = new User("Ada");
console.info(u.hello());

实例方法第一参数必须写 self（名字可改但别改）；调用时不用手动传。

02继承

Python

class Animal:
    def speak(self) -> str:
        return "..."

class Dog(Animal):
    def speak(self) -> str:
        return "woof"

print(Dog().speak())

Kotlin

open class Animal {
    open fun speak() = "..."
}
class Dog : Animal() {
    override fun speak() = "woof"
}

ArkTS

class Animal {
  speak(): string { return "..."; }
}
class Dog extends Animal {
  speak(): string { return "woof"; }
}

03@dataclass ≈ data class

Python

from dataclasses import dataclass

@dataclass
class Point:
    x: int
    y: int

p = Point(1, 2)
print(p)  # Point(x=1, y=2)

Kotlin

data class Point(val x: Int, val y: Int)
val p = Point(1, 2)
println(p)

ArkTS

// ArkTS 无内置 data class，手写字段 + 构造
class Point {
  x: number;
  y: number;
  constructor(x: number, y: number) {
    this.x = x; this.y = y;
  }
}

纯数据载体优先 @dataclass；需要行为再写普通 class。

04@property

Python

class Rect:
    def __init__(self, w: float, h: float):
        self._w, self._h = w, h

    @property
    def area(self) -> float:
        return self._w * self._h

print(Rect(3, 4).area)  # 无括号

Kotlin

class Rect(val w: Double, val h: Double) {
    val area: Double get() = w * h
}
println(Rect(3.0, 4.0).area)

ArkTS

class Rect {
  private w: number;
  private h: number;
  constructor(w: number, h: number) {
    this.w = w; this.h = h;
  }
  get area(): number {
    return this.w * this.h;
  }
}