在scala中，特征定义名称后面的花括号是什么意思？

trait MyTrait {
  // 抽象方法
  def myMethod(): Unit
  
  // 具体实现的方法
  def anotherMethod(): Unit = {
    println("This is another method.")
  }
  
  // 字段
  val myField: Int = 42
}

// 类继承特征
class MyClass extends MyTrait {
  def myMethod(): Unit = {
    println("This is my method.")
  }
}

// 混入特征
class MyMixinClass extends MyTrait {
  def myMethod(): Unit = {
    println("This is my method in the mixin class.")
  }
}

val obj1 = new MyClass()
obj1.myMethod() // 输出: This is my method.
obj1.anotherMethod() // 输出: This is another method.
println(obj1.myField) // 输出: 42

val obj2 = new MyMixinClass() with MyTrait
obj2.myMethod() // 输出: This is my method in the mixin class.
obj2.anotherMethod() // 输出: This is another method.
println(obj2.myField) // 输出: 42