我这门课叫Container
:
public class Container {
private final Map<String, Object> map = new HashMap<>();
public void put(String name, Object value) {
map.put(name, value);
}
public Container with(String name, Object value) {
put(name, value);
return this;
}
public Object get(String name) {
return map.get(name);
}
public <R> R get(String name, Function<Object, R> mapper) {
Object value = get(name);
if (null == value) {
return null;
}
return mapper
.apply(value);
}
public <R> R get(String name, Class<R> type) {
Object value = get(name);
if (null == value) {
return null;
}
if (type.isAssignableFrom(value.getClass())) {
return type
.cast(value);
}
throw new ClassCastException(String
.format("%s -> %s", value.getClass(), type));
}
}
班级叫Token
:
public class Token {
private String value;
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
public Token withValue(String value) {
setValue(value);
return this;
}
}
最后是一个测试类Token
class
public class TokenTest {
@Test
public void verifyToken() {
verify("bar", new Token()
.withValue("bar"));
}
@Test
public void verifyContainer() {
Container tokens = new Container()
.with("foo", "bar")
.with("baz", "bat");
verify("bar", tokens.get("foo", String.class));
verify("bat", tokens.get("baz", String::valueOf)); // line 21
}
private void verify(String expected, String actual) {
verify(expected, new Token()
.withValue(actual));
}
private void verify(String expected, Token actual) {
Assert
.assertEquals(expected, actual.getValue());
}
}
测试在 eclipse 中编译并运行得很好。
在命令行上构建时
mvn clean test
出现编译错误:
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.0:testCompile (default-testCompile) on project ambiguous: Compilation failure
[ERROR] /C:/data/projects/java/ambiguous/src/test/java/ambiguous/TokenTest.java:[21,9] reference to verify is ambiguous
[ERROR] both method verify(java.lang.String,java.lang.String) in ambiguous.TokenTest and method verify(java.lang.String,ambiguous.Token) in ambiguous.TokenTest match
当我换行时编译也失败21
到其中之一
verify("bat", tokens.get("baz", e -> String.valueOf(e)));
verify("bat", tokens.get("baz", e -> e.toString));
当我将线路更改为其中之一时
verify("bat", tokens.get("baz", String.class));
verify("bat", tokens.get("baz", Object::toString));
编译成功。
我不明白为什么会出现这个编译错误。
我发现了以下链接装箱和拆箱, 多种泛型类型和交集类型和这个Eclipse 编译器错误但我仍然无法理解上述原因。
我的问题是,是什么让编译器认为verify
映射器时方法匹配String::valueOf
被传递到get
method?
使用以下 jdk 进行编译(使用 maven 和 gradle):
$ java -version
openjdk version "1.8.0_201-1-ojdkbuild"
OpenJDK Runtime Environment (build 1.8.0_201-1-ojdkbuild-b09)
OpenJDK 64-Bit Server VM (build 25.201-b09, mixed mode)