如何在Scala中将定义为基类类型的变量设置为派生类型实例？

Question

在Java中，我可以将变量声明为基类类型，并将其设置为派生类型实例：

public class MyClass {
    Base foo;

    public void method(){
        foo = new Derived()
    }
}

我如何在Scala中执行此操作？

Answer 1

class Base
class Derived extends Base

class MyClass {

  var foo: Base = _ // careful, this is null until it's initialized

  def method() = {
    foo = new Derived
  }

}