JAVA规范学习——static成员初始化

class Super { static int taxi = 1729; } class Sub extends Super { static { System.out.print("Sub "); } } class Test { public static void main(String[] args) { System.out.println(Sub.taxi); } }

输出：1729

知识要点：

A reference to a class field causes initialization of only the class or interface
that actually declares it, even though it might be referred to through the name of a
subclass, a subinterface, or a class that implements an interface.

也就是说只有使用该类或者接口直接定义的类变量，才会激发该类的初始化；如果使用的是其父类定义的类变量，则子类不会被初始化

interface I { int i = 1, ii = Test.out("ii", 2); } interface J extends I { int j = Test.out("j", 3), jj = Test.out("jj", 4); } interface K extends J { int k = Test.out("k", 5); } class Test { public static void main(String[] args) { System.out.println(J.i); System.out.println(K.j); } static int out(String s, int i) { System.out.println(s + "=" + i); return i; } }

输出：

1
j=3
jj=4
3

知识要点：

Initialization of an interface does not, of itself, cause initialization of any of its
superinterfaces.

The reference to J.i is to a field that is a compile-time constant; therefore, it
does not cause I to be initialized. The reference to K.j is a reference to a field
actually declared in interface J that is not a compile-time constant; this causes initialization
of the fields of interface J, but not those of its superinterface I, nor
those of interface K. Despite the fact that the name K is used to refer to field j of
interface J, interface K is not initialized.