ArkTS 基础语法速通

let count: number = 0;     // 可变
const name: string = 'Hi'; // 不可变(推荐)
let tag = 'new';           // 类型可省略

var count: Int = 0          // 可变
val name: String = "Hi"     // 不可变(推荐)
val tag = "new"            // 类型可省略

int count = 0;              // 可变
final String name = "Hi";   // 不可变
var tag = "new";           // Java 10+ 推断

let x = 5;        // 推断 number
const s = 'hi';   // 推断 string
let ok = true;    // 推断 boolean

val x = 5        // 推断 Int
val s = "hi"      // 推断 String
val ok = true      // 推断 Boolean

var x = 5;       // 推断 int
var s = "hi";     // 推断 String
var ok = true;    // 推断 boolean

class User {
  name: string;
  private age: number = 0;
  constructor(name: string) {
    this.name = name;
  }
  sayHi(): string {
    return `Hi, I am ${this.name}`;
  }
}

class User(val name: String) {
  private var age: Int = 0
  fun sayHi(): String = "Hi, I am $name"
}

public class User {
  public final String name;
  private int age = 0;
  public User(String name) {
    this.name = name;
  }
  public String sayHi() {
    return "Hi, I am " + name;
  }
}

interface Shape {
  area(): number;
}
class Circle implements Shape {
  private r: number;
  constructor(r: number) { this.r = r; }
  area(): number {
    return Math.PI * this.r * this.r;
  }
}

interface Shape {
  fun area(): Double
}
class Circle(private val r: Double) : Shape {
  override fun area(): Double = Math.PI * r * r
}

interface Shape {
  double area();
}
class Circle implements Shape {
  private final double r;
  Circle(double r) { this.r = r; }
  public double area() {
    return Math.PI * r * r;
  }
}

let name: string | null = null;

// 严格空安全：必须判空
if (name !== null) {
  console.log(name.length);
}
// 可选链（类似 Kotlin ?.）
const len = name?.length;

var name: String? = null

// 安全调用
val len = name?.length

// 配合 let 处理非空
name?.let { println(it.length) }

// 非空断言（谨慎）
val s = name!!

String name = null;

// 手动判空（无编译期强制）
if (name != null) {
  System.out.println(name.length());
}

// 或 Optional（更啰嗦）
Optional<String> n = Optional.empty();

let nums: number[] = [1, 2, 3];
nums.forEach(n => console.log(n));

const doubled = nums.map(n => n * 2);
const even = nums.filter(n => n % 2 === 0);

// 不可变用 const + 不复写
const total = nums.reduce((a, b) => a + b, 0);

val nums = listOf(1, 2, 3)
nums.forEach { println(it) }

val doubled = nums.map { it * 2 }
val even = nums.filter { it % 2 == 0 }

val total = nums.sum()
// 或 nums.fold(0) { a, b -> a + b }

List<Integer> nums = List.of(1, 2, 3);
nums.forEach(n -> System.out.println(n));

List<Integer> doubled = nums.stream()
    .map(n -> n * 2)
    .toList();
// 可变集合用 ArrayList

interface Point {
  x: number;
  y: number;
}
const p: Point = { x: 1, y: 2 };

// ⚠️ ArkTS 禁止解构赋值
const x = p.x;
const y = p.y;

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

// Kotlin 支持解构
val (x, y) = p
println(p.x)

record Point(int x, int y) {}
Point p = new Point(1, 2);
System.out.println(p.x());

class Box<T> {
  private value: T;
  constructor(v: T) { this.value = v; }
  get(): T { return this.value; }
}
const b = new Box<string>('hi');

class Box<T>(private val value: T) {
  fun get(): T = value
}
val b = Box("hi")   // 自动推断

class Box<T> {
  private final T value;
  Box(T value) { this.value = value; }
  T get() { return value; }
}
Box<String> b = new Box<>("hi");

enum Color {
  Red, Green, Blue
}
const c: Color = Color.Red;

enum class Color {
  RED, GREEN, BLUE
}
val c = Color.RED

enum Color {
  RED, GREEN, BLUE
}
Color c = Color.RED;