【Kotlin】Kotlin笔记5-面向对象编程3(数据类,单例类)

Kotlin笔记5-面向对象编程3-数据类,单例类

3.3 面向对象编程3

• 数据类

Java实现数据类

public class Cellphone {
  String brand;
  double price;

  public Cellphone(String brand, double price){
    this.brand = brand;
    this.price = price;
  }

  @Override
  public boolean equals(Object object){
    return brand.hasCode() + (int) price;
  }
  
  @Override
  public String toString(){
    return "Cellphone(brand=" + brand + ", price=" + price + ")";
  }
}

Kotlin数据类

data

data class Cellphone(val brand: String, val price: Double)

fun main() {
    val cellphone = Cellphone("xiaomi", 4399.0)
    val cellphone2 = Cellphone("xiaomi", 4399.0)
    println(cellphone)
    println("cellphone equals cellphone2 " + (cellphone == cellphone2))
}

• 单例类

常见Java写法

class Singleton {
    private static Singleton instance;

    private Singleton(){}

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

    public void singletonTest(){
        System.out.println("singletonTest is called");
    }
}

​​调用:​​

Singleton singleton = Singleton.getInstance();
singleton.singletonTest();

Kotlin单例类

object

object Singleton {
  fun singletonTest() {
    println("singletonTest is called.")
  }
}

​​调用:​​

Singleton.singletonTest()