单选题

请问属于单例模式的类是？（） public class A{ private static A a = new A(); private A(){}; public static A getA(){ return a; } } public class B{ private static B b = null; private B(){}; public static B getB(){ b = new B(); return b; } } public class C{ private static C c = null; static{ c = new C(); } private C(){}; public static C getC(){ return c; } }

Question

A. classA和classB

B. classB和classC

C. 只有classA

D. classA 和classC