Kotlin多彩的类——数据类

1. 关键字： data
2. 必须有一个构造方法；
3. 主构造方法中的属性必须由var/val修饰
4. 数据类不能是抽象类、open类、封闭（sealed）类或内部类；
5. 不可以继承任何类，但是可以实现接口
6. 数据类类似我们Java中Bean类
7. 在主构造函数里所声明的所有属性，编译器都会根据这些属性自动生成以下方法:toString,hashCode,equals,其中equals不是比较两个对象的地址，而是比较两个对象的主构造函数中的属性值
8. 类对象里，主构造函数中有几个属性，会有几个这个方法componentN()
9. copy()函数:需要复制一个类对象，但是改变它的某些属性，保持剩余其他的属性值不变。
10. 数据类和解构声明：
    数据类生成的组件功能能够在解构声明使用：

var ( age,name, sex) = dataClass2
    println("name = $name,age=$age,Sex=$sex")

解构声明中参数的顺序和主构造函数中参数相同

package classes

import javafx.scene.text.FontWeight

data class DataClass(val name: String, val age: Int, val sex: String) {

    var weight: Float = 0.0f
        get() = field
        set(value) {
            field = value
        }

    constructor(weight: Float) : this(name = "Tom", age = 18, sex = "男") {

    }
}

反编译成java类，注意观察toString,hashCode,equals，验证7中总结的

``
package classes;

public final class DataClass {
   private float weight;
   @NotNull
   private final String name;
   private final int age;
   @NotNull
   private final String sex;

   public final float getWeight() {
      return this.weight;
   }

   public final void setWeight(float var1) {
      this.weight = var1;
   }

   @NotNull
   public final String getName() {
      return this.name;
   }

   public final int getAge() {
      return this.age;
   }

   @NotNull
   public final String getSex() {
      return this.sex;
   }

   public DataClass(@NotNull String name, int age, @NotNull String sex) {
      Intrinsics.checkParameterIsNotNull(name, "name");
      Intrinsics.checkParameterIsNotNull(sex, "sex");
      super();
      this.name = name;
      this.age = age;
      this.sex = sex;
   }

   public DataClass(float weight) {
      this("Tom", 18, "男");
   }

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

   public final int component2() {
      return this.age;
   }

   @NotNull
   public final String component3() {
      return this.sex;
   }

   @NotNull
   public final DataClass copy(@NotNull String name, int age, @NotNull String sex) {
      Intrinsics.checkParameterIsNotNull(name, "name");
      Intrinsics.checkParameterIsNotNull(sex, "sex");
      return new DataClass(name, age, sex);
   }

   // $FF: synthetic method
   // $FF: bridge method
   @NotNull
   public static DataClass copy$default(DataClass var0, String var1, int var2, String var3, int var4, Object var5) {
      if ((var4 & 1) != 0) {
         var1 = var0.name;
      }

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

      if ((var4 & 4) != 0) {
         var3 = var0.sex;
      }

      return var0.copy(var1, var2, var3);
   }

   public String toString() {
      return "DataClass(name=" + this.name + ", age=" + this.age + ", sex=" + this.sex + ")";
   }

   public int hashCode() {
      return ((this.name != null ? this.name.hashCode() : 0) * 31 + this.age) * 31 + (this.sex != null ? this.sex.hashCode() : 0);
   }

   public boolean equals(Object var1) {
      if (this != var1) {
         if (var1 instanceof DataClass) {
            DataClass var2 = (DataClass)var1;
            if (Intrinsics.areEqual(this.name, var2.name) && this.age == var2.age && Intrinsics.areEqual(this.sex, var2.sex)) {
               return true;
            }
         }

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

Main函数

package classes

fun main(args: Array) {
    var dataClass = DataClass(140.00F)
    dataClass.weight = 140F
    println(dataClass.weight)
    println(dataClass.toString())

    var dataClass1 = DataClass(140.00F)
    dataClass1.weight = 150F
    println(dataClass1.weight)
    println(dataClass1.toString())

    println(dataClass1.component1())
    println(dataClass1.component2())
    println(dataClass1.component3())
    println(dataClass1.equals(dataClass))
    var dataClass2 = dataClass.copy(age = 19)
    println(dataClass2.component1())
    println(dataClass2.component2())
    println(dataClass2.component3())
    println(dataClass1.equals(dataClass2))
    var ( age,name, sex) = dataClass2
    println("name = $name,age=$age,Sex=$sex")

}

运行结果

140.0
DataClass(name=Tom, age=18, sex=男)
150.0
DataClass(name=Tom, age=18, sex=男)
Tom
18
男
true
Tom
19
男
false
name = 19,age=Tom,Sex=男