java - 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();
}

为什么这不是一个抽象方法

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，6287639是 bug id，它说，

JDK-6287639 : Abstract methods in enum classes should not be listed as abstract

现在考虑下面的 enum，将其视为类，并将每个枚举常量视为 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种convert不是abstract，

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