Java 类文件规范 - double 和长整型表示

Question

在 Java 类文件规范中，关于 long and double representation 的部分，文档说:

The CONSTANT_Long_info and CONSTANT_Double_info represent 8-byte numeric (long and double) constants:

CONSTANT_Long_info {
    u1 tag;
    u4 high_bytes;
    u4 low_bytes;
}

CONSTANT_Double_info {
    u1 tag;
    u4 high_bytes;
    u4 low_bytes;
}

All 8-byte constants take up two entries in the constant_pool table of the class file. If a CONSTANT_Long_info or CONSTANT_Double_info structure is the item in the constant_pool table at index n, then the next usable item in the pool is located at index n+2. The constant_pool index n+1 must be valid but is considered unusable.

我的疑问是索引n+1中constant_pool中条目的tag是什么。

Answer 1

索引n+1处没有标记，因为索引n+1处没有常量池条目。它就像索引 0 一样。没有数据，它会直接跳到下一个条目。