[Kotlin入门] 单例、数据类、静态

一. 数据类

1. 基础用法

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

自动生成了get set hashcode equals toString等方法。通过反编译(打开AS，在Tools-Kotlin-ShowBytecode-Decompile)可以得到如下结果

public final class Cellphone {
   @NotNull
   private final String brand;
   private final double price;

   @NotNull
   public final String getBrand() {
      return this.brand;
   }

   public final double getPrice() {
      return this.price;
   }

   public Cellphone(@NotNull String brand, double price) {
      Intrinsics.checkNotNullParameter(brand, "brand");
      super();
      this.brand = brand;
      this.price = price;
   }

   @NotNull
   public final String component1() {
      return this.brand;
   }

   public final double component2() {
      return this.price;
   }

   @NotNull
   public final Cellphone copy(@NotNull String brand, double price) {
      Intrinsics.checkNotNullParameter(brand, "brand");
      return new Cellphone(brand, price);
   }

   // $FF: synthetic method
   public static Cellphone copy$default(Cellphone var0, String var1, double var2, int var4, Object var5) {
      if ((var4 & 1) != 0) {
         var1 = var0.brand;
      }

      if ((var4 & 2) != 0) {
         var2 = var0.price;
      }

      return var0.copy(var1, var2);
   }

   @NotNull
   public String toString() {
      return "Cellphone(brand=" + this.brand + ", price=" + this.price + ")";
   }

   public int hashCode() {
      String var10000 = this.brand;
      return (var10000 != null ? var10000.hashCode() : 0) * 31 + Double.hashCode(this.price);
   }

   public boolean equals(@Nullable Object var1) {
      if (this != var1) {
         if (var1 instanceof Cellphone) {
            Cellphone var2 = (Cellphone)var1;
            if (Intrinsics.areEqual(this.brand, var2.brand) && Double.compare(this.price, var2.price) == 0) {
               return true;
            }
         }

         return false;
      } else {
         return true;
      }
   }
}

2. 进阶

参考文献

2.1 去除自动生成的get()/set()方法

@JvmField

2.2 更换自动生成的get、set方法名

2.3 多个构造方法

data class Child @JvmOverloads constructor(
    var age: Int,
    var name: String = ""
)

@JvmOverloads用法介绍

2.4 componentN()

二. 单例

class改成object，其他的跟java里面差不多

object Singleton {
}

三. 静态

companion object
@JvmField - 修饰静态变量
@JvmStatic - 修饰静态方法
@JvmField 和 @JvmStatic 只能写在 object 修饰的类或者 companion object 里，写法虽然有些别扭，但是效果是真的是按 static 来实现的

class BookKotlin {
    companion object {
        @JvmField
        var nameStatic: String = "BB"
        @JvmStatic
        fun speakStatic() {
        }
    }
}