• JAVA 对象拷贝


    1.java里的clone分为: 
    A:浅复制(浅克隆): 浅复制仅仅复制所考虑的对象,而不复制它所引用的对象。 
    b:深复制(深克隆):深复制把要复制的对象所引用的对象都复制了一遍。 
    Java中对象的克隆,为了获取对象的一份拷贝,我们可以利用Object类的clone()方法。必须要遵循下面三点 
    1.在派生类中覆盖基类的clone()方法,并声明为public【Object类中的clone()方法为protected的】。 
    2.在派生类的clone()方法中,调用super.clone()。 
    3.在派生类中实现Cloneable接口。 

    Object类里的clone方法是浅复制(浅克隆) 

    浅复制(浅克隆)的例子如下: 

    public class CloneTest
    {
    
    	public static void main(String[] args) throws Exception
    	{
    		// teacher对象将被clone出来的Student对象共享.
    		Teacher teacher = new Teacher();
    		teacher.setAge(40);
    		teacher.setName("Teacher zhang");
    
    		Student student1 = new Student();
    		student1.setAge(20);
    		student1.setName("zhangsan");
    		student1.setTeacher(teacher);
    
    		// 复制出来一个对象student2
    		Student student2 = (Student) student1.clone();
    		System.out.println(student2.getAge());
    		System.out.println(student2.getName());
    
    		System.out.println("~~~~~~~~~~~~~~~~~~~~~~");
    		System.out.println(student1.getTeacher().getAge());
    		System.out.println(student1.getTeacher().getName());
    
    		// 修改student2的引用对象
    		student2.getTeacher().setAge(50);
    		student2.getTeacher().setName("Teacher Li");
    
    		System.out.println("~~~~~~~~~~~~~~~~~~~~~~");
    		System.out.println(student1.getTeacher().getAge());
    		System.out.println(student1.getTeacher().getName());
    	}
    }
    
    class Teacher
    {
    	public int age;
    	public String name;
    
    	public int getAge()
    	{
    		return age;
    	}
    
    	public void setAge(int age)
    	{
    		this.age = age;
    	}
    
    	public String getName()
    	{
    		return name;
    	}
    
    	public void setName(String name)
    	{
    		this.name = name;
    	}
    
    }
    
    class Student implements Cloneable
    {
    
    	public int age;
    	public String name;
    	public Teacher teacher;
    
    	public int getAge()
    	{
    		return age;
    	}
    
    	public void setAge(int age)
    	{
    		this.age = age;
    	}
    
    	public String getName()
    	{
    		return name;
    	}
    
    	public void setName(String name)
    	{
    		this.name = name;
    	}
    
    	public Teacher getTeacher()
    	{
    		return teacher;
    	}
    
    	public void setTeacher(Teacher teacher)
    	{
    		this.teacher = teacher;
    	}
    
    	@Override
    	public Object clone() throws CloneNotSupportedException
    	{
    		return super.clone();
    	}
    }
    输出结果为:
    20
    zhangsan
    ~~~~~~~~~~~~~~~~~~~~~~
    40
    Teacher zhang
    ~~~~~~~~~~~~~~~~~~~~~~
    50
    Teacher Li


    2.深复制(深Clone)例子:

    public class DeepCloneTest
    {
    
    	public static void main(String[] args) throws Exception
    	{
    		// teacher对象将不被clone出来的Student对象共享.
    		Teacher teacher = new Teacher();
    		teacher.setAge(40);
    		teacher.setName("Teacher zhang");
    
    		Student student1 = new Student();
    		student1.setAge(20);
    		student1.setName("zhangsan");
    		student1.setTeacher(teacher);
    
    		// 复制出来一个对象student2
    		Student student2 = (Student) student1.clone();
    		System.out.println(student2.getAge());
    		System.out.println(student2.getName());
    
    		System.out.println("~~~~~~~~~~~~~~~~~~~~~~");
    		System.out.println(student1.getTeacher().getAge());
    		System.out.println(student1.getTeacher().getName());
    
    		// 修改student2的引用对象
    		student2.getTeacher().setAge(50);
    		student2.getTeacher().setName("Teacher Li");
    
    		System.out.println("~~~~~~~~~~~~~~~~~~~~~~");
    		System.out.println(student1.getTeacher().getAge());
    		System.out.println(student1.getTeacher().getName());
    	}
    }
    
    class Teacher implements Cloneable
    {
    	public int age;
    	public String name;
    
    	public int getAge()
    	{
    		return age;
    	}
    
    	public void setAge(int age)
    	{
    		this.age = age;
    	}
    
    	public String getName()
    	{
    		return name;
    	}
    
    	public void setName(String name)
    	{
    		this.name = name;
    	}
    
    	@Override
    	public Object clone() throws CloneNotSupportedException
    	{
    		return super.clone();
    	}
    
    }
    
    class Student implements Cloneable
    {
    
    	public int age;
    	public String name;
    	public Teacher teacher;
    
    	public int getAge()
    	{
    		return age;
    	}
    
    	public void setAge(int age)
    	{
    		this.age = age;
    	}
    
    	public String getName()
    	{
    		return name;
    	}
    
    	public void setName(String name)
    	{
    		this.name = name;
    	}
    
    	public Teacher getTeacher()
    	{
    		return teacher;
    	}
    
    	public void setTeacher(Teacher teacher)
    	{
    		this.teacher = teacher;
    	}
    
    	@Override
    	public Object clone() throws CloneNotSupportedException
    	{
    		Student student = (Student) super.clone();
    		// 将引用的对象teacher也clone下
    		student.setTeacher((Teacher) (student.getTeacher().clone()));
    		return student;
    	}
    }
    
    输出结果为:
    20
    zhangsan
    ~~~~~~~~~~~~~~~~~~~~~~
    40
    Teacher zhang
    ~~~~~~~~~~~~~~~~~~~~~~
    40
    Teacher zhang
    

    3.利用序列化来做深复制,把对象写到流里的过程是序列化(Serilization)过程,而把对象从流中读出来的过程则叫做反序列化(Deserialization)过程。应当指出的是,写在流里的是对象的一个拷贝,而原对象仍然存在于JVM里面。,利用这个特性,可以做深拷贝 。

    import java.io.ByteArrayInputStream;
    import java.io.ByteArrayOutputStream;
    import java.io.ObjectInputStream;
    import java.io.ObjectOutputStream;
    import java.io.Serializable;
    //利用序列化来做深复制
    //深clone
    
    public class DeepCloneTest
    {
    
    	public static void main(String[] args) throws Exception
    	{
    		// teacher对象将不被clone出来的Student对象共享.
    		Teacher teacher = new Teacher();
    		teacher.setAge(40);
    		teacher.setName("Teacher zhang");
    
    		Student student1 = new Student();
    		student1.setAge(20);
    		student1.setName("zhangsan");
    		student1.setTeacher(teacher);
    
    		// 复制出来一个对象student2
    		Student student2 = (Student) student1.deepCopy();
    		System.out.println(student2.getAge());
    		System.out.println(student2.getName());
    
    		System.out.println("~~~~~~~~~~~~~~~~~~~~~~");
    		System.out.println(student1.getTeacher().getAge());
    		System.out.println(student1.getTeacher().getName());
    
    		// 修改student2的引用对象
    		student2.getTeacher().setAge(50);
    		student2.getTeacher().setName("Teacher Li");
    
    		System.out.println("~~~~~~~~~~~~~~~~~~~~~~");
    		System.out.println(student1.getTeacher().getAge());
    		System.out.println(student1.getTeacher().getName());
    	}
    }
    
    class Teacher implements Serializable
    {
    
    	private static final long serialVersionUID = -8834559347461591191L;
    
    	public int age;
    	public String name;
    
    	public int getAge()
    	{
    		return age;
    	}
    
    	public void setAge(int age)
    	{
    		this.age = age;
    	}
    
    	public String getName()
    	{
    		return name;
    	}
    
    	public void setName(String name)
    	{
    		this.name = name;
    	}
    
    }
    
    class Student implements Serializable
    {
    
    	// serialVersionUID
    	// 如果你的对象序列化后存到硬盘上面后,可是后来你却更改了类的field(增加或减少或改名),当你反序列化时,就会出现Exception的,这样就会造成不兼容性的问题。
    	// 但当serialVersionUID相同时,它就会将不一样的field以type的缺省值赋值(如int型的是0,String型的是null等),这个可以避开不兼容性的问题。所以最好给serialVersionUID赋值
    	private static final long serialVersionUID = 7991552226614088458L;
    
    	public int age;
    	public String name;
    	public Teacher teacher;
    
    	public int getAge()
    	{
    		return age;
    	}
    
    	public void setAge(int age)
    	{
    		this.age = age;
    	}
    
    	public String getName()
    	{
    		return name;
    	}
    
    	public void setName(String name)
    	{
    		this.name = name;
    	}
    
    	public Teacher getTeacher()
    	{
    		return teacher;
    	}
    
    	public void setTeacher(Teacher teacher)
    	{
    		this.teacher = teacher;
    	}
    
    	public Object deepCopy() throws Exception
    	{
    		// 将该对象序列化成流,因为写在流里的是对象的一个拷贝,而原对象仍然存在于JVM里面。所以利用这个特性可以实现对象的深拷贝
    		ByteArrayOutputStream bos = new ByteArrayOutputStream();
    
    		ObjectOutputStream oos = new ObjectOutputStream(bos);
    
    		oos.writeObject(this);
    
    		// 将流序列化成对象
    		ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
    
    		ObjectInputStream ois = new ObjectInputStream(bis);
    
    		return ois.readObject();
    	}
    }
    
    输出结果为:
    20
    zhangsan
    ~~~~~~~~~~~~~~~~~~~~~~
    40
    Teacher zhang
    ~~~~~~~~~~~~~~~~~~~~~~
    40
    Teacher zhang
    


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  • 原文地址:https://www.cnblogs.com/jdluojing/p/3212447.html
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