Java中替代C# ref/out 关键字方案:

刚学习Java不久，今天遇到一个问题，需要在方法中修改传入的对象的值，确切的说是需要使用一个方法，创建一个对象，并把其引用返回，熟悉C#的我
的第一反应就是C#中的ref/out关键字,结果发现Java中没有类似的关键字，所以只能想想如何解决此问题.

---

参数传递:
方法的参数传递有两种，一种是值传递，一种是引用传递,但是其实都是拷贝传递。

值传递：就是把传递的【数据本身拷贝一份】，传入方法中对其进行操作，拷贝的是值。
引用传递：就是把指向某个对象的【引用拷贝一份】，传入方法中通过此引用可以对对象进行操作。

---

那么就我当前的问题而言，我需要一个方法，我传入一个引用，在方法中创建所需对象.

那么在Java中就会只能给当前对象在封装一层（定义一个新类），使得需要创建的对象成为新类的成员，在方法中为成员赋值

---

Example:

C#:

    /// <summary>

    /// model

    /// </summary>

    public class Student

    {

        public string Name;

        public int Age;

    }

        /// 方法:

        /// <summary>

        /// 错误示范

        /// 

        /// student这个引用是拷贝传入的，创建新的对应Student 

        /// 把引用赋给student，当方法退栈之后student引用回到压栈前

        /// 则Student对象引用数为0，等待GC，引用student依旧是原来的值(逻辑地址)

        /// </summary>

        /// <param name="student"></param>

        static void createStudent(Student student)

        {

            student = new Student { Name ="Stephen Lee", Age = 1};

        }

        /// <summary>

        /// 正确做法

        /// 

        /// 通过ref关键字，把操作权让给方法内部

        /// </summary>

        /// <param name="student"></param>

        static void createStudent(ref Student student)

        {

            student = new Student { Name = "Stephen Lee", Age = 1 };

        }

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

        // Client

        static void Main(string[] args)

        {

            Console.WriteLine("错误示范");

            Student student1 = null;

            createStudent(student1);

            if (student1 == null)

                Console.WriteLine("创建对象失败");

            else

                Console.WriteLine("创建对象成功,Name:" + student1.Name);

            Console.WriteLine("正确做法");

            Student student2 = null;

            createStudent(ref student2);

            if (student2 == null)

                Console.WriteLine("创建对象失败");

            else

                Console.WriteLine("创建对象成功,Name:" + student2.Name);

        }

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

Java:

/** Model

 * @author Stephen

 *

 */

public class Student

{

    public String Name;

    public int Age;

    public Student(String name,int age)

    {

        this.Name = name;

        this.Age = age;

    }

}

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

    /** 错误示范,原因同C#

     * @param student

     */

    private void createStudent(Student student)

    {

        student = new Student("Stephen Lee",1);

    }

    /** 正确做法

     * @param studentPack

     */

    private void createStudent(StudentPack studentPack)

    {

        studentPack.student = new Student("Stephen Lee",1);

    }

    /** 包装器

     * @author Stephen

     *

     */

    public class StudentPack

    {

        public Student student;

    }

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

        // Client

        StudentPack studentPack = new StudentPack();

        createStudent(studentPack);

        System.out.println(studentPack.student.Name);

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

ref/out关键字:http://msdn.microsoft.com/zh-cn/library/14akc2c7.aspx