.Net C#语法 构造函数中this和base

public class TestClassA
{
public TestClassA()
{
Console.WriteLine("我是在TestClassA中的TestClassA()构造函数中");
}
public TestClassA(string a, string b)
{
Console.WriteLine("我是在TestClassA中的TestClassA(string a, string b)构造函数中");
}
public TestClassA(string a)
: this(a, "b")
{
Console.WriteLine("我是在TestClassA中的TestClassA(string a): this(a, \"b\")构造函数中");
}
}

public class TestClassB : TestClassA
{
public TestClassB()
{
Console.WriteLine("我是在TestClassB中的TestClassB()构造函数中");
}
public TestClassB(string a, string b)
: base(a, b)
{
Console.WriteLine("我是在TestClassB中的TestClassB(string a, string b): base(a, b)构造函数中");
}

public TestClassB(string a)
: this(a, "b")
{
Console.WriteLine("我是在TestClassB中的TestClassB(string a, string b): this(a, \"b\")构造函数中");
}
}

Console.WriteLine("TestClassA Father1 = new TestClassA();运行结果：");
TestClassA Father1 = new TestClassA();
Console.WriteLine();
Console.WriteLine("TestClassA Father2 = new TestClassA(\"f2\", \"f2\");运行结果：");
TestClassA Father2 = new TestClassA("f2", "f2");
Console.WriteLine();
Console.WriteLine("TestClassA Father3 = new TestClassA(\"f3\");运行结果：");
TestClassA Father3 = new TestClassA("f3");
Console.WriteLine();
Console.WriteLine("TestClassB Son1 = new TestClassB();运行结果：");
TestClassB Son1 = new TestClassB();
Console.WriteLine();
Console.WriteLine("TestClassB Son2 = new TestClassB(\"s2\", \"s2\");运行结果：");
TestClassB Son2 = new TestClassB("s2", "s2");
Console.WriteLine();
Console.WriteLine("TestClassB Son3 = new TestClassB(\"s3\");运行结果：");
TestClassB Son3 = new TestClassB("s3");
Console.WriteLine();