C++初始化列表

#include<iostream>
using namespace std;

class firstClass
{
	private:
		int a,b;
	public:
		firstClass(int mya,int myb){a=mya;b=myb;}
		int geta(){return a;}
		int getb(){return b;}
};

class Test1
{
	private:
		int a,b;
	public:
		Test1(int mya,int myb){a=mya;b=myb;}
		int geta(){return a;}
		int getb(){return b;}
};

class Test2 :public firstClass
{
	private:
		int c,d;
		Test1 test1;
	public:
		Test2(int x,int y):firstClass(111,222),test1(2,3),c(x),d(y){}
		void show(){
			cout<<geta()<<endl;
			cout<<getb()<<endl;
			cout<<test1.geta()<<endl;
			cout<<test1.getb()<<endl;
			cout<<c<<endl;
			cout<<d<<endl;
		}
};

int main()
{
	Test2 test2(22,33);
	test2.show();
	return 0;
}