下面是一个简单的类(可在repo中复制):
import static org.hamcrest.*;
import static org.junit.Assert.assertThat;
import java.util.*;
import org.junit.Test;
public class TestGenerics {
@Test
public void thisShouldCompile() {
List<String> myList = Arrays.asList("a", "b", "c");
assertThat("List doesn't contain unexpected elements", myList, not(anyOf(hasItem("d"), hasItem("e"), hasItem("f"))));
}
}
行为取决于JDK版本:
- 在JDK<=8(已测试7和8)中正常编译
- 使用JDK 9+(已测试9、10和11 EA)编译失败
将出现以下错误:
[ERROR] /tmp/jdk-issue-generics/src/test/java/org/alostale/issues/generics/TestGenerics.java:[17,17] no suitable method found for assertThat(java.lang.String,java.util.List<java.lang.String>,org.hamcrest.Matcher<java.lang.Iterable<? super java.lang.Object>>)
method org.junit.Assert.<T>assertThat(java.lang.String,T,org.hamcrest.Matcher<? super T>) is not applicable
(inference variable T has incompatible bounds
upper bounds: java.lang.String,java.lang.Object
lower bounds: capture#1 of ? super T?,capture#2 of ? super java.lang.Object,capture#3 of ? super java.lang.Object,java.lang.Object,java.lang.String,capture#4 of ? super T?)
method org.junit.Assert.<T>assertThat(T,org.hamcrest.Matcher<? super T>) is not applicable
(cannot infer type-variable(s) T
(actual and formal argument lists differ in length))
这是JDK 9中的一些预期更改还是一个bug?
我可以通过以下方式将匹配器提取到已输入的变量中,使其正常工作:
Matcher<Iterable<? super String>> m1 = hasItem("d");
Matcher<Iterable<? super String>> m2 = hasItem("e");
Matcher<Iterable<? super String>> m3 = hasItem("f");
assertThat(myList, not(anyOf(m1, m2, m3)));
但问题仍然是:是否正确,javac
<=8 能够推断类型,但在9+中却不能?
junit:4.12
中的Assert
类是使用Java5编译的(类版本为49.0)...如果这可能会提供任何线索:) - Naman