C#构造函数的继承和引用方法 override

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace practise1
{
    class Program
    {
        static void Main(string[] args)
        {
            TestCon con = new TestCon();
            Console.WriteLine(con.ToString());
            TestA testA1 = new TestA();
            Console.WriteLine("测试类A无参数构造方法");
            Console.WriteLine(testA1.ToString());
            Console.WriteLine();

            TestA testA2 = new TestA("Set First Param");
            Console.WriteLine("测试类A一个参数构造方法");
            Console.WriteLine(testA2.ToString());
            Console.WriteLine();

            TestB testB1 = new TestB();
            Console.WriteLine("测试类B无参数构造方法");
            Console.WriteLine(testB1.ToString());
            Console.WriteLine();

            TestB testB2 = new TestB("Set First Param");
            Console.WriteLine("测试类B一个参数构造方法");
            Console.WriteLine(testB2.ToString());
            Console.WriteLine();

            TestB testB3 = new TestB("Set First Param", "Set Second Param");
            Console.WriteLine("测试类B两个参数构造方法");
            Console.WriteLine(testB3.ToString());
            Console.WriteLine();

            TestB testB4 = new TestB("Set First Param", "Set Second Param", "Set Third Param");
            Console.WriteLine("测试类B三个参数构造方法");
            Console.WriteLine(testB4.ToString());
            Console.WriteLine();

            Console.ReadLine();
        }


        class TestCon
        {
            private string _a = "_a1";
            private string _b = "_b2";
        }

        /// <summary> 
        /// 测试类A 
        /// </summary> 
        class TestA
        {
            protected string _testValueA;

            /// <summary> 
            /// 无参数构造方法 
            /// </summary> 
            public TestA() : this("Set First Param")
            {

            }

            /// <summary> 
            /// 一个参数构造方法 
            /// </summary> 
            /// <param name="value"></param> 
            public TestA(string value)
            {
                _testValueA = value;
            }

            /// <summary> 
            /// 重新ToString方法 
            /// </summary> 
            /// <returns></returns> 
            public override string ToString()
            {
                return this._testValueA;
            }
        }

        /// <summary> 
        /// 测试类TestB，从TestA类中继承 
        /// </summary> 
        class TestB : TestA
        {
            protected string _testValueB;
            protected string _testValueC;
            /// <summary> 
            /// 调用父类中的构造方法 
            /// </summary> 
            public TestB() : base()
            {
                this._testValueB = "Set Second Param";
                this._testValueC = "Set Third Param";
            }
            /// <summary> 
            /// 调用父类中的构造方法 
            /// </summary> 
            /// <param name="valueA"></param> 
            public TestB(string valueA)
            : base(valueA)
            {
                this._testValueB = "Set Second Param";
                this._testValueC = "Set Third Param";
            }

            /// <summary> 
            /// 调用其他构造方法 
            /// </summary> 
            /// <param name="valueA"></param> 
            /// <param name="valueB"></param> 
            public TestB(string valueA, string valueB)
            : this(valueA, valueB, "Set Third Param")
            {

            }
            /// <summary> 
            /// 三个参数的构造方法 
            /// </summary> 
            /// <param name="valueA"></param> 
            /// <param name="valueB"></param> 
            /// <param name="valueC"></param> 
            public TestB(string valueA, string valueB, string valueC)
            {
                this._testValueA = valueA;
                this._testValueB = valueB;
                this._testValueC = valueC;
            }

            /// <summary> 
            /// 重新ToString方法 
            /// </summary> 
            /// <returns></returns> 
            public override string ToString()
            {
                return this._testValueA + "\n" + this._testValueB + "\n" + this._testValueC;
            }
        }
    }
}