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程序員的成長(zhǎng)之路

互聯(lián)網(wǎng)/程序員/技術(shù)/資料共享?

閱讀本文大概需要 4 分鐘。

作者：riemann
blog.csdn.net/riemann_/article/details/87217229

一、拷貝的引入

（1）、引用拷貝

創(chuàng)建一個(gè)指向?qū)ο蟮囊米兞康目截悺?/p>

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

輸出結(jié)果：

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

結(jié)果分析：由輸出結(jié)果可以看出，它們的地址值是相同的，那么它們肯定是同一個(gè)對(duì)象。teacher和otherteacher的只是引用而已，他們都指向了一個(gè)相同的對(duì)象Teacher(“Taylor”,26)。這就叫做引用拷貝。

（2）、對(duì)象拷貝

創(chuàng)建對(duì)象本身的一個(gè)副本。

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

輸出結(jié)果：

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

結(jié)果分析：由輸出結(jié)果可以看出，它們的地址是不同的，也就是說創(chuàng)建了新的對(duì)象，而不是把原對(duì)象的地址賦給了一個(gè)新的引用變量,這就叫做對(duì)象拷貝。

注：深拷貝和淺拷貝都是對(duì)象拷貝

二、淺拷貝

（1）、定義

被復(fù)制對(duì)象的所有變量都含有與原來的對(duì)象相同的值，而所有的對(duì)其他對(duì)象的引用仍然指向原來的對(duì)象。即對(duì)象的淺拷貝會(huì)對(duì)“主”對(duì)象進(jìn)行拷貝，但不會(huì)復(fù)制主對(duì)象里面的對(duì)象。”里面的對(duì)象“會(huì)在原來的對(duì)象和它的副本之間共享。

簡(jiǎn)而言之，淺拷貝僅僅復(fù)制所考慮的對(duì)象，而不復(fù)制它所引用的對(duì)象

（2）、淺拷貝實(shí)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("拷貝后");
????????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("修改老師的信息后-------------");
????????//?修改老師的信息
????????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;
????}
}

輸出結(jié)果：

拷貝后
edgar
18
riemann
27
修改老師的信息后-------------
Games
Games

結(jié)果分析：兩個(gè)引用student1和student2指向不同的兩個(gè)對(duì)象，但是兩個(gè)引用student1和student2中的兩個(gè)teacher引用指向的是同一個(gè)對(duì)象，所以說明是淺拷貝。

三、深拷貝

（1）、定義

深拷貝是一個(gè)整個(gè)獨(dú)立的對(duì)象拷貝，深拷貝會(huì)拷貝所有的屬性,并拷貝屬性指向的動(dòng)態(tài)分配的內(nèi)存。當(dāng)對(duì)象和它所引用的對(duì)象一起拷貝時(shí)即發(fā)生深拷貝。深拷貝相比于淺拷貝速度較慢并且花銷較大。

簡(jiǎn)而言之，深拷貝把要復(fù)制的對(duì)象所引用的對(duì)象都復(fù)制了一遍。

（2）、深拷貝實(shí)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("拷貝后");
????????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("修改老師的信息后-------------");
????????//?修改老師的信息
????????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?{
????????//?淺復(fù)制時(shí)：
????????//?Object?object?=?super.clone();
????????//?return?object;

????????//?改為深復(fù)制：
????????Student3?student?=?(Student3)?super.clone();
????????//?本來是淺復(fù)制，現(xiàn)在將Teacher對(duì)象復(fù)制一份并重新set進(jìn)來
????????student.setTeacher((Teacher2)?student.getTeacher().clone());
????????return?student;

????}
}

輸出結(jié)果：

拷貝后
edgar
18
riemann
27
修改老師的信息后-------------
Games
riemann

結(jié)果分析：

兩個(gè)引用student1和student2指向不同的兩個(gè)對(duì)象，兩個(gè)引用student1和student2中的兩個(gè)teacher引用指向的是兩個(gè)對(duì)象，但對(duì)teacher對(duì)象的修改只能影響student1對(duì)象,所以說是深拷貝。