为什么IsIterableContainingInOrder Hamcrest匹配器无法使用数组？

Question

我显然很困惑如何使用Hamcrest IsIterableContainingInOrder来验证List的相等性而不仅仅是使用.equals().我想在报告中看到Hamcrest的有用信息.

为什么下面的测试甚至无法编译？其中一些比其他人更反直觉,至少对我而言.我认为,我得到的一般原则是类型参数将被推断为我传递给具有varargs签名的方法,因此它会将T的数组视为T的变量,因此将生成基于T的匹配器,而不是T的数组,可迭代的T或类似的东西.

我可以使用一个解释,为什么一些最直观的行实际上甚至无法编译.

尤其:

• 图3和4显示了数组/列表的不对称性
• 5和6显示我可以查看List而不是数组(？)

标记为这样的行上的编译器警告对我来说更加神秘.

---

@org.junit.Test
public void testTest() {
  String string1 = "A";
  String string2 = "B";
  String string3 = "C";

  List<String> list1 = Lists.newArrayList(string1, string2, string3);
  List<String> list2 = Lists.newArrayList(string1, string2, "C");

  String[] array1 = list1.toArray(new String[list1.size()]);
  String[] array2 = list2.toArray(new String[list2.size()]);

  // -------------------------------------------------------------------------
  // 1) The assertion after this comment line DOES NOT COMPILE
  // Assert.assertThat(array2, IsIterableContainingInOrder.contains(array1));
  // -------------------------------------------------------------------------
  // 2) The assertion after this comment line DOES NOT COMPILE
  // Assert.assertThat(list2, IsIterableContainingInOrder.contains(list1));
  // -------------------------------------------------------------------------
  // 3) The assertion after this comment line SUCCEEDS
  Assert.assertThat(list2, IsIterableContainingInOrder.contains(array1));
  // -------------------------------------------------------------------------
  // 4) The assertion after this comment line DOES NOT COMPILE + HAS WARNING
  // Assert.assertThat(array2, IsIterableContainingInOrder.contains(list1));
  // -------------------------------------------------------------------------
  // 5) The assertion after this comment line DOES NOT COMPILE
  // Assert.assertThat(array2, IsIterableContainingInOrder.contains(string1));
  // -------------------------------------------------------------------------
  // 6) The assertion after this comment line COMPILES but fails
  Assert.assertThat(list2, IsIterableContainingInOrder.contains(string1));
  // -------------------------------------------------------------------------
  // 7) The assertion after this comment line COMPILES and succeeds
  Assert.assertThat(list2,
      IsIterableContainingInOrder.contains(string1, string2, string3));
  // -------------------------------------------------------------------------
}

---

大量的惊讶.:(

---

PS我意识到所有的惊讶都来自于我自己的无知而没有别的.我应该了解泛型,类型推理,变量等等.我真的可以对此进行彻底的解释,我可能会在未来几次回顾它.

PPS我确实尝试先读取代码但是看了一会儿......;)不是为了佯攻:

@SuppressWarnings("unchecked")
@Factory
public static <E> Matcher<Iterable<? extends E>> contains(final Matcher<? super E> itemMatcher) {
    return contains(new ArrayList<Matcher<? super E>>(asList(itemMatcher)));
}

Answer 1

这是下水道......希望是正确的:)

// 1) The assertion after this comment line DOES NOT COMPILE
// Assert.assertThat(array2, IsIterableContainingInOrder.contains(array1));

这个不会编译,因为数组不实现Iteratable.

// 2) The assertion after this comment line DOES NOT COMPILE
// Assert.assertThat(list2, IsIterableContainingInOrder.contains(list1));

为此,list2应该是a List<List<String>>,因为只包含验证iteratable包含传递的项目

// 3) The assertion after this comment line SUCCEEDS
Assert.assertThat(list2, IsIterableContainingInOrder.contains(array1));

通过,因为array1被视为vararg.

// 4) & 5) 

与1相同

// 6) The assertion after this comment line COMPILES but fails
Assert.assertThat(list2, IsIterableContainingInOrder.contains(string1));

Contains需要集合中的所有项目,而不仅仅是子集.

// 7)

类似于3,但每个项目都通过了.