Java的深拷贝和浅拷贝的区别

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一、拷贝的引入


(1)、引用拷贝

创建一个指向对象的引用变量的拷贝。

Teacher teacher = new Teacher("Taylor",26; Teacher otherteacher = teacher; System.out.println(teacher; System.out.println(otherteacher;

输出结果:

blog.Teacher@355da254 blog.Teacher@355da254

结果分析:由输出结果可以看出,它们的地址值是相同的,那么它们肯定是同一个对象。teacher和otherteacher的只是引用而已,他们都指向了一个相同的对象Teacher(“Taylor”,26。这就叫做引用拷贝。


(2)、对象拷贝

创建对象本身的一个副本。

Teacher teacher = new Teacher("Swift",26; Teacher otherteacher = (Teacherteacher.clone(; System.out.println(teacher; System.out.println(otherteacher;

输出结果:

blog.Teacher@355da254 blog.Teacher@4dc63996

注:深拷贝和浅拷贝都是对象拷贝

二、浅拷贝


(1)、定义

被复制对象的所有变量都含有与原来的对象相同的值,而所有的对其他对象的引用仍然指向原来的对象。即对象的浅拷贝会对“主”对象进行拷贝,但不会复制主对象里面的对象。”里面的对象“会在原来的对象和它的副本之间共享。

简而言之,浅拷贝仅仅复制所考虑的对象,而不复制它所引用的对象

(2)、浅拷贝实例

package com.test; public class ShallowCopy { public static void main(String[] args throws CloneNotSupportedException { Teacher teacher = new Teacher(; teacher.setName("riemann"; teacher.setAge(27; Student2 student1 = new Student2(; student1.setName("edgar"; student1.setAge(18; student1.setTeacher(teacher; Student2 student2 = (Student2 student1.clone(; System.out.println("拷贝后"; System.out.println(student2.getName(; System.out.println(student2.getAge(; System.out.println(student2.getTeacher(.getName(; System.out.println(student2.getTeacher(.getAge(; System.out.println("修改老师的信息后-------------"; // 修改老师的信息 teacher.setName("Games"; System.out.println(student1.getTeacher(.getName(; System.out.println(student2.getTeacher(.getName(; } } class Teacher implements Cloneable { private String name; private int age; public String getName( { return name; } public void setName(String name { this.name = name; } public int getAge( { return age; } public void setAge(int age { this.age = age; } } class Student2 implements Cloneable { private String name; private int age; private Teacher teacher; public String getName( { return name; } public void setName(String name { this.name = name; } public int getAge( { return age; } public void setAge(int age { this.age = age; } public Teacher getTeacher( { return teacher; } public void setTeacher(Teacher teacher { this.teacher = teacher; } public Object clone( throws CloneNotSupportedException { Object object = super.clone(; return object; } }

输出结果:

拷贝后 edgar 18 riemann 27 修改老师的信息后------------- Games Games

结果分析:两个引用student1和student2指向不同的两个对象,但是两个引用student1和student2中的两个teacher引用指向的是同一个对象,所以说明是浅拷贝。

三、深拷贝


(1)、定义

深拷贝是一个整个独立的对象拷贝,深拷贝会拷贝所有的属性,并拷贝属性指向的动态分配的内存。当对象和它所引用的对象一起拷贝时即发生深拷贝。深拷贝相比于浅拷贝速度较慢并且花销较大。

简而言之,深拷贝把要复制的对象所引用的对象都复制了一遍。

(2)、深拷贝实例

package com.test; public class DeepCopy { public static void main(String[] args throws CloneNotSupportedException { Teacher2 teacher = new Teacher2(; teacher.setName("riemann"; teacher.setAge(27; Student3 student1 = new Student3(; student1.setName("edgar"; student1.setAge(18; student1.setTeacher(teacher; Student3 student2 = (Student3 student1.clone(; System.out.println("拷贝后"; System.out.println(student2.getName(; System.out.println(student2.getAge(; System.out.println(student2.getTeacher(.getName(; System.out.println(student2.getTeacher(.getAge(; System.out.println("修改老师的信息后-------------"; // 修改老师的信息 teacher.setName("Games"; System.out.println(student1.getTeacher(.getName(; System.out.println(student2.getTeacher(.getName(; } } class Teacher2 implements Cloneable { private String name; private int age; public String getName( { return name; } public void setName(String name { this.name = name; } public int getAge( { return age; } public void setAge(int age { this.age = age; } public Object clone( throws CloneNotSupportedException { return super.clone(; } } class Student3 implements Cloneable { private String name; private int age; private Teacher2 teacher; public String getName( { return name; } public void setName(String name { this.name = name; } public int getAge( { return age; } public void setAge(int age { this.age = age; } public Teacher2 getTeacher( { return teacher; } public void setTeacher(Teacher2 teacher { this.teacher = teacher; } public Object clone( throws CloneNotSupportedException { // 浅复制时: // Object object = super.clone(; // return object; // 改为深复制: Student3 student = (Student3 super.clone(; // 本来是浅复制,现在将Teacher对象复制一份并重新set进来 student.setTeacher((Teacher2 student.getTeacher(.clone(; return student; } }

输出结果:

拷贝后 edgar 18 riemann 27 修改老师的信息后------------- Games riemann

结果分析:

两个引用student1和student2指向不同的两个对象,两个引用student1和student2中的两个teacher引用指向的是两个对象,但对teacher对象的修改只能影响student1对象,所以说是深拷贝。

关于Java深拷贝和浅拷贝区别,你学废了么?

    区别:如果在拷贝这个对象的时候,只对基本数据类型进行了拷贝,而对引用类型数据只是进行了引用的传递,而没有真实的创建一个新的对象,则认为是浅拷贝。反之,在对引用类型数据进行拷贝的时候,创建了一个新的对象,并且复制其内的成员变量,则认为是深拷贝。

问:clone(方法,是对当前对象进行浅拷贝,引用类型依然是在传递引用,那么,如何进行一个深拷贝呢?

    序列化这个对象,再反序列化回来,就可得到这个新的对象,无非就是序列化的规则需要自己来写。
  • 继续利用clone(方法,既然clone(方法是我们来重写的,实际上可以对其内的引用类型的变量,在进行一次clone(。

编程笔记 » Java的深拷贝和浅拷贝的区别

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