Java编译器:具有相同名称和不同签名的两个方法如何与一个方法调用匹配? [英] Java compiler: How can two methods with the same name and different signatures match a method call?
问题描述
我有一个叫做Container
的课程:
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));
}
}
和名为Token
的类:
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Token
类的测试类
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());
}
}
该测试仅在Eclipse中编译并运行文件.
The test compiles and runs just file in eclipse.
在通用线路上构建时
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
当我将行21
更改为其中之一时,编译也会失败
The compilation also fails when I change line 21
to one of
verify("bat", tokens.get("baz", e -> String.valueOf(e)));
verify("bat", tokens.get("baz", e -> e.toString));
当我将行更改为其中之一
When I change the line to one of
verify("bat", tokens.get("baz", String.class));
verify("bat", tokens.get("baz", Object::toString));
编译成功.
我无法理解为什么会出现这种编译错误.
I cannot undestand why this compiliation error is raised.
我遇到了以下链接:装箱和拆箱 ,多个通用类型和交集类型和此 eclipse编译器错误,但我仍然无法关联原因.
I came across the follwong links boxing and unboxing, multiple generic types and intersection types and this eclipse compiler bug but I still cannot relate to the mentioned causes.
我的问题是,当映射器String::valueOf
传递给get
方法时,是什么使编译器认为verify
方法的两个签名都匹配?
My question is, what makes the compiler think that both signatures of the verify
method are matching when the mapper String::valueOf
is passed to the get
method?
要进行编译,请使用以下jdk(带有maven和gradle):
For compilation the following jdk is used (with maven and 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)