string的相关细节

首先,string 是引用类型

那么
string s1 ="Hello World!!"
string s2 ="Hello World!!"
是否是相同的引用?
string s3=s1+"!";
string s4=s1+"!";
是否是相同的引用?

string s5 ="Hello World!!"
string s6="Hello "+"World!!"
是否是相同的引用?

string s7=s1+"";
string s8=s1+"";
是否是相同的引用?

string s9="";
string s10=string.Empty;
是否是相同的引用?

由于在string中 "=="已经被重载为对值的比较而不是对引用的比较,所以比较时请使用object.ReferenceEquals()

    public class MyString
    {

        /// <summary>
        /// ==在string的比较中被重载为对值的比较
        /// </summary>
        public void TheEqualMarks()
        {
            string s1 = "Hello";
            string s2 = "Hello";

            if (s1 == s2)
            {
                Console.WriteLine("== is true");
            }
            else
            {
                Console.WriteLine("== is False");
            }

            s1 += "World!";
            s2 += "World!";


            if (s1 == s2)
            {
                Console.WriteLine("== is true");
            }
            else
            {
                Console.WriteLine("== is False");
            }

        }

        /// <summary>
        /// 声明两个相同值的字符串时,其引用是相同的,
        /// "Hello World!!"与"Hello "+"World!!"指向相同引用
        /// 使用string的引用进行+操作符时,会返回不同的地址引用,例如s9,s10的比较
        /// +""时,扔指向原来的引用
        /// </summary>
        public void TheReferenceEquals()
        {
            string s1 = "Hello";
            string s2 = "Hello";

            if (Object.ReferenceEquals(s1,s2))
            {
                Console.WriteLine("ReferenceEquals is true");
            }
            else
            {
                Console.WriteLine("ReferenceEquals is False");
            }

            s1 += "";
            s2 += "";

            if (Object.ReferenceEquals(s1, s2))
            {
                Console.WriteLine("used += \"\"   ReferenceEquals is true");
            }
            else
            {
                Console.WriteLine("used += \"\"   ReferenceEquals is False");
            }

            s1 += "World!";
            s2 += "World!";

            if (Object.ReferenceEquals(s1, s2))
            {
                Console.WriteLine("ReferenceEquals is true");
            }
            else
            {
                Console.WriteLine("ReferenceEquals is False");
            }

            string s3 = "Hello World!!";
            string s4 = "Hello ";
            string s5 = "World!!";

            string s6 = "Hello " + "World!!";
            string s7 = s4 + s5;

            if (Object.ReferenceEquals(s3, s6))
            {
                Console.WriteLine("s3, s6 TheReferenceEquals is true");
            }
            else
            {
                Console.WriteLine("s3, s6 TheReferenceEquals is False");
            }

            if (Object.ReferenceEquals(s3, s7))
            {
                Console.WriteLine("s3, s7 TheReferenceEquals is true");
            }
            else
            {
                Console.WriteLine("s3, s7 TheReferenceEquals is False");
            }

            s1 = "Hello";
            s2 = "Hello";

            string s9 = s1 + s2;
            string s10 = s1 + s2;
            if (Object.ReferenceEquals(s9, s10))
            {
                Console.WriteLine("s9, s10 ReferenceEquals is true");
            }
            else
            {
                Console.WriteLine("s9, s10 ReferenceEquals is False");
            }

        }

        public void TheEquals()
        {

            string s1 = "Hello";
            string s2 = "Hello";

            if (s1.Equals(s2))
            {
                Console.WriteLine("Equals is true");
            }
            else
            {
                Console.WriteLine("Equals is False");
            }
            s1 += "World!";
            s2 += "World!";
            if (s1.Equals(s2))
            {
                Console.WriteLine("Equals is true");
            }
            else
            {
                Console.WriteLine("Equals is False");
            }

        }

        /// <summary>
        /// string.Empty与""指向相同引用
        /// </summary>
        public void TheStringEmpty()
        {

            string s1 = string.Empty;
            string s2 = "";

            if(object.ReferenceEquals(s1,s2))
            {
                Console.WriteLine("string.Empty, \"\"    ReferenceEquals is true");
            }

        }

    }