如何在斯卡拉

Question

使用Java自我约束类

说我有这种自我约束的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); 
    } 
} 

此代码给了我2倍“测试”，如我所料。

但我努力写相同的斯卡拉：

如果我没有通过它成为一个SelfBounded [没什么]类型。但是尝试使用SelfBounded类型，如'：SelfBounded [SelfBounded]'，由于递归性质，它给了我麻烦，编译器告诉我每个'SelfBounded'都需要一个类型参数。

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，而不改变SelfBounded类的定义？

注意：这是一个简化的例子，同时尝试在Scala中使用testcontainers-java。

Answer 1

当您在Java中编写SelfBounded selfBounded = new SelfBounded()时，您使用的是raw types，它仅存在于与预代数代码兼容的代码中。不要这样做。正确的方法是延长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); 
    } 
} 

同样在Scala中，只是它不支持原始类型，因为它有始以来类型参数：

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

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