java - 为什么静态初始化块中不允许有限定的静态最终变量？

Question

情况1

class Program {
    static final int var;

    static {
        Program.var = 8;  // Compilation error
    }

    public static void main(String[] args) {
        int i;
        i = Program.var;
        System.out.println(Program.var);
    }
}

案例2

class Program {
    static final int var;

    static {
        var = 8;  //OK
    }

    public static void main(String[] args) {
        System.out.println(Program.var);
    }
}

为什么情况 1会导致编译错误？

Answer 1

JLS 给出了答案（注意粗体声明）：

同样，每个空白的 final 变量最多只能赋值一次；当对它进行分配时，它必须绝对未分配。当且仅当变量的简单名称（或者，对于字段，其简单名称由此限定）出现在赋值运算符的左侧时，才定义这样的赋值。[ §16 ]

这意味着在分配静态最终变量时必须使用“简单名称” - 即没有任何限定符的 var 名称。

Answer 2

Apparently this is a cheap syntactic trick to limit definite (un)assignment analysis within the class itself.

If the field is syntactically qualified with a class name, the code is usually in another class, where the analysis cannot reach.

This trick fails in your example. Other examples of oddity:

static class A
{
    static final int a;
    static
    {
        // System.out.println(a); // illegal
        System.out.println(A.a);  // compiles!
        a = 1;
    }
}

If they had more resources, they probably would've made a finer rule. But we can't change spec now.