歡迎大家關注我的公衆号【老周聊架構】,Java後端主流技術棧的原理、源碼分析、架構以及各種網際網路高并發、高性能、高可用的解決方案。
一、拷貝的引入
(1)、引用拷貝
建立一個指向對象的引用變量的拷貝。
public class QuoteCopy {
public static void main(String[] args) {
Teacher teacher = new Teacher("riemann", 28);
Teacher otherTeacher = teacher;
System.out.println(teacher);
System.out.println(otherTeacher);
}
}
class Teacher {
private String name;
private int age;
public Teacher(String name, int age) {
this.name = name;
this.age = 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;
}
}
輸出結果:
com.test.Teacher@28a418fc
com.test.Teacher@28a418fc
結果分析:由輸出結果可以看出,它們的位址值是相同的,那麼它們肯定是同一個對象。teacher和otherTeacher的隻是引用而已,他們都指向了一個相同的對象Teacher(“riemann”,28)。 這就叫做引用拷貝。
(2)、對象拷貝
建立對象本身的一個副本。
public class ObjectCopy {
public static void main(String[] args) throws CloneNotSupportedException {
Teacher teacher = new Teacher("riemann", 28);
Teacher otherTeacher = (Teacher) teacher.clone();
System.out.println(teacher);
System.out.println(otherTeacher);
}
}
class Teacher implements Cloneable {
private String name;
private int age;
public Teacher(String name, int age) {
this.name = name;
this.age = 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 {
Object object = super.clone();
return object;
}
}
輸出結果:
com.test.Teacher@28a418fc
com.test.Teacher@5305068a
結果分析:由輸出結果可以看出,它們的位址是不同的,也就是說建立了新的對象, 而不是把原對象的位址賦給了一個新的引用變量,這就叫做對象拷貝。
注:深拷貝和淺拷貝都是對象拷貝
二、淺拷貝
(1)、定義
被複制對象的所有變量都含有與原來的對象相同的值,而所有的對其他對象的引用仍然指向原來的對象。即對象的淺拷貝會對“主”對象進行拷貝,但不會複制主對象裡面的對象。”裡面的對象“會在原來的對象和它的副本之間共享。
簡而言之,淺拷貝僅僅複制所考慮的對象,而不複制它所引用的對象。
(2)、淺拷貝執行個體
public class ShallowCopy {
public static void main(String[] args) throws CloneNotSupportedException {
Teacher teacher = new Teacher();
teacher.setName("riemann");
teacher.setAge(28);
Student student1 = new Student();
student1.setName("edgar");
student1.setAge(18);
student1.setTeacher(teacher);
Student student2 = (Student) student1.clone();
System.out.println("-------------拷貝後-------------");
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("-------------修改老師的資訊後-------------");
// 修改老師的資訊
teacher.setName("jack");
System.out.println("student1的teacher為: " + student1.getTeacher().getName());
System.out.println("student2的teacher為: " + 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 Student 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;
}
}
輸出結果:
-------------拷貝後-------------
edgar
18
riemann
28
-------------修改老師的資訊後-------------
student1的teacher為: jack
student2的teacher為: jack
結果分析: 兩個引用student1和student2指向不同的兩個對象,但是兩個引用student1和student2中的兩個teacher引用指向的是同一個對象,是以說明是淺拷貝。
三、深拷貝
(1)、定義
深拷貝是一個整個獨立的對象拷貝,深拷貝會拷貝所有的屬性,并拷貝屬性指向的動态配置設定的記憶體。當對象和它所引用的對象一起拷貝時即發生深拷貝。深拷貝相比于淺拷貝速度較慢并且花銷較大。
簡而言之,深拷貝把要複制的對象所引用的對象都複制了一遍。
(2)、深拷貝執行個體
public class DeepCopy {
public static void main(String[] args) throws CloneNotSupportedException {
Teacher teacher = new Teacher();
teacher.setName("riemann");
teacher.setAge(28);
Student student1 = new Student();
student1.setName("edgar");
student1.setAge(18);
student1.setTeacher(teacher);
Student student2 = (Student) student1.clone();
System.out.println("-------------拷貝後-------------");
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("-------------修改老師的資訊後-------------");
// 修改老師的資訊
teacher.setName("jack");
System.out.println("student1的teacher為: " + student1.getTeacher().getName());
System.out.println("student2的teacher為: " + 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;
}
public Object clone() throws CloneNotSupportedException {
return super.clone();
}
}
class Student 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 {
// 淺複制時:
// Object object = super.clone();
// return object;
// 改為深複制:
Student student = (Student) super.clone();
// 本來是淺複制,現在将Teacher對象複制一份并重新set進來
student.setTeacher((Teacher) student.getTeacher().clone());
return student;
}
}
輸出結果:
-------------拷貝後-------------
edgar
18
riemann
28
-------------修改老師的資訊後-------------
student1的teacher為: jack
student2的teacher為: riemann
結果分析:
兩個引用student1和student2指向不同的兩個對象,兩個引用student1和student2中的兩個teacher引用指向的是兩個對象,但對teacher對象的修改隻能影響student1對象,是以說是深拷貝。