private void button2_Click(object sender, EventArgs e)
{
Class3 parent;
Class4 c4 = new Class4();
parent = c4; //上溯造型,父类（接口）变量指向子类对象。
MessageBox.Show(parent.GetString());
Class5 c5 = new Class5();
parent = c5; //上溯造型,父类（接口）变量指向子类对象。
MessageBox.Show(parent.GetString());
}
private void button9_Click(object sender, EventArgs e)
{
OOHandler o = new OOHandler();
Class3 parent;
parent = new Class4();
this.textBox1.Text = o.HandleParentObject(parent);
parent = new Class5();
this.textBox2.Text = o.HandleParentObject(parent);
}
