Mockito：带有界限通配符的归类方法 [英] Mockito: Stubbing Methods That Return Type With Bounded Wild-Cards

问题描述

请考虑下面的代码：

  public class DummyClass {
 public List< ;?扩展Number> dummyMethod（）{
返回新的ArrayList< Integer>（）; 
 
 
 $ / code $ / pre 
 
 
  public class DummyClassTest {
 public void testMockitoWithGenerics（）{
 DummyClass dummyClass = Mockito.mock（DummyClass.class）; 
列表< ;?扩展Number> someList = new ArrayList< Integer>（）; 
 Mockito.when（dummyClass.dummyMethod（））。thenReturn（someList）; //编译器抱怨这个
 
 
  
编译器抱怨该行试图为 dummyMethod（）存根行为。任何关于如何使用有界通配符返回类型的stubbing方法的指针？
    您也可以使用非类型安全方法 doReturn 为此目的， 
 
  @Test 
 public void testMockitoWithGenerics（）
 {
 DummyClass dummyClass = Mockito.mock（DummyClass.class）; 
列表< ;?扩展Number> someList = new ArrayList< Integer>（）; 
 
 Mockito.doReturn（someList）.when（dummyClass）.dummyMethod（）; 
 
 Assert.assertEquals（someList，dummyClass.dummyMethod（））; 
} 
  
为讨论 Mockito的谷歌组。  
 
 
尽管这比 thenAnswer 简单，但请注意它不是类型安全的。如果您担心类型安全，Millhouse的答案是正确的。  
 
 
其他详细信息
 
 
 
要清楚，以下是观察到的编译器错误，
 
 
然后返回类型为OngoingStubbing< List<捕获＃1-of？的方法返回（List< capture＃1 of？extends Number>扩展Number>>不适用于参数（List< capture＃2-of？extends Number>）
 
我相信编译器已经分配了第一个通配符类型在时调用，然后无法确认 thenReturn 调用中的第二个通配符类型是否相同。  
 
 
它看起来像 thenAnswer 不会遇到这个问题，因为它接受通配符类型，而然后返回采用一个非通配符类型，必须被捕获。从Mockito的 OngoingStubbing ， 
 
 
  OngoingStubbing< T> thenAnswer（Answer<？> answer）; 
 OngoingStubbing< T>然后返回（T值）; 
  
 
Consider this code:
public class DummyClass {
    public List<? extends Number> dummyMethod() {
        return new ArrayList<Integer>();
    }
}


public class DummyClassTest {
    public void testMockitoWithGenerics() {
        DummyClass dummyClass = Mockito.mock(DummyClass.class);
        List<? extends Number> someList = new ArrayList<Integer>();
        Mockito.when(dummyClass.dummyMethod()).thenReturn(someList); //Compiler complains about this
    }
}
The compiler complains about the line that's trying to stub the behavior for dummyMethod(). Any pointers on how one goes about stubbing methods that return a type with bounded wild-cards?
解决方案
You can also use the non-type safe method doReturn for this purpose,
@Test
public void testMockitoWithGenerics()
{
    DummyClass dummyClass = Mockito.mock(DummyClass.class);
    List<? extends Number> someList = new ArrayList<Integer>();

    Mockito.doReturn(someList).when(dummyClass).dummyMethod();

    Assert.assertEquals(someList, dummyClass.dummyMethod());
}
as discussed on Mockito's google group.  


While this is simpler than thenAnswer, again note that it is not type safe.  If you're concerned about type safety, millhouse's answer is correct.  

Additional Details

To be clear, here's the observed compiler error,

  
The method thenReturn(List<capture#1-of ? extends Number>) in the type OngoingStubbing<List<capture#1-of ? extends Number>> is not applicable for the arguments (List<capture#2-of ? extends Number>)
I believe the compiler has assigned the first wildcard type during the when call and then cannot confirm that the second wildcard type in the thenReturn call is the same.   

It looks like thenAnswer doesn't run into this issue because it accepts a wildcard type while thenReturn takes a non-wildcard type, which must be captured.  From Mockito's OngoingStubbing,
OngoingStubbing<T> thenAnswer(Answer<?> answer);
OngoingStubbing<T> thenReturn(T value);


                        
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