首先我们来看一下值类型怎么复制,看下面的代码:

   public class ValcpyDemo
    {
        public ValcpyDemo()
        {
            int x = 0;
            int y = x;
            x = 1;
            System.out.println("y = " + y);
        }

        public static void main(String[] args)
        {
            new ValcpyDemo();
        }

    }

    public class ValcpyDemo
    {
        public ValcpyDemo()
        {
            int x = 0;
            int y = x;
            x = 1;
            System.out.println("y = " + y);
        }

        public static void main(String[] args)
        {
            new ValcpyDemo();
        }

    }

    结果显而易见:y的值为0 也就是说,对于基本类型的变量来说,通过简单赋值就可以实现值变量的拷贝.

     但是对于对象类型来说,情况却不那么简单.

    看下面的代码:

    public class ObjcpyDemo
    {
        public ObjcpyDemo()
        {
            // 定义student1对象变量
            Student student1 = new Student();
            student1.id = "0001";
            student1.name = "Tom";
            // 将student1赋值给student2
            Student student2 = student1;
            student1.id = "0002";
            student1.name = "Jack";

            System.out.println("student2.id = " + student2.id);
            System.out.println("student2.name = " + student2.name);
        }

        public static void main(String[] args)
        {
            new ObjcpyDemo();
        }

    }

    public class ObjcpyDemo
    {
        public ObjcpyDemo()
        {
            // 定义student1对象变量
            Student student1 = new Student();
            student1.id = "0001";
            student1.name = "Tom";
            // 将student1赋值给student2
            Student student2 = student1;
            student1.id = "0002";
            student1.name = "Jack";

            System.out.println("student2.id = " + student2.id);
            System.out.println("student2.name = " + student2.name);
        }

        public static void main(String[] args)
        {
            new ObjcpyDemo();
        }

    }

结果是:

     student2.id = 0002

    student2.name = jack

    对象变量student2从student1赋值得到,而且在student1值发生改变的同时, student2对象的属性值也相应的改变了,看起来student1和student2指向的是同一个对象(即同一块内存),根本没有达到复制的目的.

    这是为什么呢?原来对象类型 变量的复制,不能和简单类型变量一般,而必须引用Object.Clone()方法,否则赋予的 只是对象的引用而已. 而直接或者间接的使用Object.Clone()方法,来实现Clone的对象也有"浅层克隆"和"深层克隆"的说法,将在另一片文章中描述.

    那么,让我们最后看一下字符串的拷贝又是怎么一回事呢?

    虽然String类型也是继承自Object,但对于字符串来说,情况显得有点特殊.对于String类型的赋值是创建一个新的String对象,而不仅仅是将对象 引用赋值给对方.从这个意义上讲,对String的赋值更类似于基本类型.

    下面是示例:

   public class StrcpyDemo
    {
        public StrcpyDemo()
        {
            String s1 = "1";
            String s2 = s1;
            s1 = "2";
            System.out.println("s2 = " + s2);
        }

        public static void main(String[] args)
        {
            new StrcpyDemo();
        }
    }

    public class StrcpyDemo
    {
        public StrcpyDemo()
        {
            String s1 = "1";
            String s2 = s1;
            s1 = "2";
            System.out.println("s2 = " + s2);
        }

        public static void main(String[] args)
        {
            new StrcpyDemo();
        }
    }

    答案:

    s2 = 1

    总结:

    对于基本类型,通过简单赋值就可以实现值变量的拷贝.

    对象类型 变量的复制,不能和简单类型变量一般,而必须引用Object.Clone()方法,否则赋予的 只是对象的引用而已.

    对于String类型的赋值是创建一个新的String对象,而不仅仅是将对象 引用赋值给对方.从这个意义上讲,对String的赋值更类似于基本类型.