我意识到Java 8仍然在测试版，但是这一点让我很奇怪：

public class Fields> {

public Fields(Set columns) {

// A sample column used to find the universe of the enum of Columns.

C sampleCol = columns.iterator().next();

// Java 8 needs a cast here.

Set allColumns = EnumSet.allOf((/*Class)*/ sampleCol.getClass());

// ... there's more to this that I've deleted.

}

}

错误读取：

error: incompatible types: inferred type does not conform to equality constraint(s)

Set allColumns = EnumSet.allOf(sampleCol.getClass());

inferred: C

equality constraints(s): C,CAP#1

where C is a type-variable:

C extends Enum declared in class Test.Fields

where CAP#1 is a fresh type-variable:

CAP#1 extends Enum from capture of ? extends Enum

这是Java 8的一个bug还是新功能？