Question

说我有这个自我约束的java类：

public class SelfBounded<SELF extends SelfBounded<SELF>> {
    public String testField = "TEST";

    public SelfBounded() {

    }

    public SELF testMethod() {
        return (SELF) this;
    }
}

在Java中我们可以这样写：

public class SelfBoundedMainJava {
    public static void main(String[] args) {
        SelfBounded selfBounded = new SelfBounded();
        System.out.println(selfBounded.testField);
        System.out.println(selfBounded.testMethod().testField);
    }
}

这段代码给了我2x＆＃34; TEST＆＃34;正如我所料。

但是我在scala中努力写出相同内容：

如果我没有通过该类型，它将成为SelfBounded [Nothing]。但是试图使用SelfBounded类型，例如在SelfBounded [SelfBounded]＆＃39;中，由于递归性质，它给我带来了麻烦，编译器告诉我每个＆＃39; SelfBounded＆＃39;需要一个类型参数。

object SelfBoundedMainScala extends App {
  // here the type of selfBounded1 is SelfBounded[Nothing]
  val selfBounded1 = new SelfBounded()
  println(selfBounded1.testField)
  // does not work since testMethod() returns a Nothing
  //println(selfBounded1.testMethod().testField)

  // trying to set the type of the selfBounded variable gives me issues because of the recursive type
  // does not compile 'class SelfBounded takes type parameters'
  // val selfBounded2: SelfBounded[SelfBounded] = new SelfBounded()
  // same issue
  // val selfBounded3 = new SelfBounded[SelfBounded]()
}

有没有办法在Scala中完成Java主类，而不更改SelfBounded类定义？

注意：尝试在Scala中使用testcontainers-java时，这是一个精简的示例。

Answer 1

当您在Java中编写SelfBounded selfBounded = new SelfBounded()时，您使用的是raw types，它仅用于与预先泛型代码兼容。不要那样做。正确的方法是扩展SelfBounded：

class SelfBounded1 extends SelfBounded<SelfBounded1> {}

public class SelfBoundedMainJava {
    public static void main(String[] args) {
        // or SelfBounded<?> selfBounded
        SelfBounded1 selfBounded = new SelfBounded1();
        System.out.println(selfBounded.testField);
        System.out.println(selfBounded.testMethod().testField);
    }
}

在Scala中也是如此，但它不支持原始类型，因为它自开始以来具有类型参数：

object SelfBoundedMainScala extends App {
  class SelfBounded1 extends SelfBounded[SelfBounded1]

  val selfBounded1 = new SelfBounded1()
  println(selfBounded1.testField)
  println(selfBounded1.testMethod().testField)
}

如何在Scala

1 个答案: