scala apply方法和update方法

示例代码1

class TestApplyClass {
  def apply(param: String): String = {
    println("apply method called, parameter is: " + param)

    return "Hello World!"
  }
}

val myObject = new TestApplyClass()
println(myObject("param1"))

输出为：

apply method called, parameter is: param1

Hello World!

示例代码2

object TestApplySingleObject {
  def apply(param1: String, param2: String): String = {
    println("apply method called")

    return param1 + " and " + param2
  }
}

// 单例对象不需要 new
val group = TestApplySingleObject("zhangfei", "liubei")
println(group)

输出：

apply method called

zhangfei and liubei

可以看出，在执行TestApplySingleObject("zhangfei", "liubei")时调用了apply方法，并且把"zhangfei and liubei"作为返回值，赋值给group变量。

输出：

apply method in object is called

Greeting menthod in class is called.

apply method in class is called!