为什么java.util.concurrent.TimeUnit.convert抛出AbstractMethodError而不是抽象

Question

java.util.concurrent.TimeUnit 有这个来源:

public long convert(long sourceDuration, TimeUnit sourceUnit) {
    throw new AbstractMethodError();
}

为什么这不是一个abstract像这样的方法

abstract int excessNanos(long d, long m);

Answer 1

方法声明上方的单行注释如下:

// To maintain full signature compatibility with 1.5, and to improve the
// clarity of the generated javadoc (see 6287639: Abstract methods in
// enum classes should not be listed as abstract), method convert
// etc. are not declared abstract but otherwise act as abstract methods. 

在这里,6287639bug id是说,

JDK-6287639:枚举类中的抽象方法不应该作为抽象列出

现在考虑以下enum将它视为类和每个枚举常量作为一个Object,很明显,如果我们创建Object一些抽象的东西,我们必须提供实现,并避免这convert不是abstract,

enum Blocks {
    A1, B1, C1;
    // It will say enum constant must implement 
    // the abstract method test
    abstract int test();
}