C# null合并运算符??

    internal class Tester {
        public void Test() {
            AAA aaa = null;
            AAA bbb = new AAA("bbb");
            Console.WriteLine(Test1(aaa, bbb).Name); //bbb
            Console.WriteLine(Test2(aaa, bbb).Name); //bbb
            aaa = aaa ?? (new AAA("aaa")); //如果aaa==null,则给aaa赋值new AAA("aaa")
            Console.WriteLine(Test1(aaa, bbb).Name); //aaa
            Console.WriteLine(Test2(aaa, bbb).Name); //aaa
            aaa = aaa ?? (new AAA("xxx")); //如果aaa==null,则给aaa赋值new AAA("xxx")
            Console.WriteLine(Test1(aaa, bbb).Name); //aaa
            Console.WriteLine(Test2(aaa, bbb).Name); //aaa
        }
        AAA Test1(AAA aaa, AAA bbb) {
            if (aaa != null) {  //aaa为不空时使用aaa
                return aaa;
            }
            return bbb; //否则使用第二个对象bbb
        }
        AAA Test2(AAA aaa, AAA bbb) {
            return aaa ?? bbb; //如果此运算符的左操作数不为null，则此运算符将返回左操作数，否则返回右操作数
        }
    }

    class AAA {
        public string Name { get; set; }
        public AAA(string name) {
            Name = name;
        }
    }