泛型类型推断不能与方法链接一起使用？

Question

该代码在Java 8中编译，但在Java 7中无法编译：class Map<K,V> {    static <K,V> Map<K,V> empty() {return null;}    Map<K,V> put(K k, V v) {return null;}    V get(K k) {return null;}}class A {    static void f(Map<Integer,String> m){}    public static void main(String[] args) {        f(Map.empty());    }}它不会推断Map从中返回的具体类型Map.empty()：$ javac7 A.javaA.java:10: error: method f in class A cannot be applied to given types;        f(Map.empty());        ^  required: Map<Integer,String>  found: Map<Object,Object>  reason: actual argument Map<Object,Object> cannot be converted to Map<Integer,String> by method invocation conversion1 error如果将f调用更改为，它将编译f(Map.<Integer,String>empty());。在Java 8中，它可以工作而不必求助于此。但是，如果将f调用更改为f(Map.empty().put(1,"A").put(2,"B"));，它将无法在Java 7和8上再次编译。为什么？$ $javac7 A.java A.java:10: error: method f in class A cannot be applied to given types;        f(Map.empty().put(1,"A").put(2,"B"));        ^  required: Map<Integer,String>  found: Map<Object,Object>  reason: actual argument Map<Object,Object> cannot be converted to Map<Integer,String> by method invocation conversion1 error$ $javac8 A.javaA.java:10: error: incompatible types: Map<Object,Object> cannot be converted to Map<Integer,String>        f(Map.empty().put(1,"A").put(2,"B"));                                    ^Note: Some messages have been simplified; recompile with -Xdiags:verbose to get full output1 error$ $javac8 -Xdiags:verbose A.javaA.java:10: error: method f in class A cannot be applied to given types;        f(Map.empty().put(1,"A").put(2,"B"));        ^  required: Map<Integer,String>  found: Map<Object,Object>  reason: argument mismatch; Map<Object,Object> cannot be converted to Map<Integer,String>1 error