淺拷貝-深拷貝總結

淺拷貝：

基本數據類型引用數據類型

值傳遞	成員變量的引用值（內存地址）復制（實際指向同一個）

深拷貝：

基本數據類型引用數據類型

值傳遞	new一個新對象，進行屬性賦值

淺拷貝兩種實現方法

1、拷貝構造函數
一個學生類，包含兩個屬性，一個是基本數據類型name，一個是引用數據類型Age

public class Boy {String name;Age age;public Boy() {}public Boy(String name, Age age) {this.name = name;this.age = age;}//拷貝構造函數，實現了對象的拷貝，基本數據類型值傳遞，引用數據類型內存地址復制public Boy(Boy b){this.age = b.age;this.name = b.name;}public Age getAge() {return age;}public void setAge(Age age) {this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}@Overridepublic String toString() {return "Boy{" +"name='" + name + '\'' +", age=" + age +'}';} }class Age{int age;public int getAge() {return age;}public void setAge(int age) {this.age = age;}public Age(int age) {this.age = age;}@Overridepublic String toString() {return "Age{" +"age=" + age +'}';} } public class Copyconstructor {public static void main(String[] args) {Age age = new Age(26);Boy boy = new Boy("pmh",age);//通過拷貝構造函數實現了對象的淺拷貝Boy boy1 = new Boy(boy);//我們通過修改其中一個去判斷boy.name = "zyf";age.setAge(99);System.out.println(boy);System.out.println(boy1);} }

結果

Boy{name='zyf', age=Age{age=99}} Boy{name='pmh', age=Age{age=99}}

2、重寫clone()方法進行淺拷貝
注意點：
1、protected native Object clone() throws CloneNotSupportedException;權限是受保護的，我們無法直接使用
2、使用clone方法的類必須實現Cloneable接口，否則會拋出異常CloneNotSupportedException

步驟如下

1、對象如果想通過clone方法實現淺拷貝，首先需要實現cloneable接口，重寫clone()方法

public class Student implements Cloneable {String name;Score score;public Student(String name, Score score) {this.name = name;this.score = score;}public Student() {}public String getName() {return name;}public void setName(String name) {this.name = name;}public Score getScore() {return score;}public void setScore(Score score) {this.score = score;}@Overridepublic String toString() {return "Student{" +"name='" + name + '\'' +", score=" + score +'}';}@Overrideprotected Object clone() throws CloneNotSupportedException {return super.clone();} }class Score{int score;public Score(int score) {this.score = score;}public int getScore() {return score;}public void setScore(int score) {this.score = score;}@Overridepublic String toString() {return "Score{" +"score=" + score +'}';} } public class CopyCloneable {public static void main(String[] args) {Score score = new Score(100);Student student = new Student("pmh",score);try {//由此我們通過實現了Cloneabe的實現類Student重寫的clone方法實現了淺拷貝Student student1 = (Student)student.clone();System.out.println(student);System.out.println(student1);student.name = "ZYhf";score.score = 99;System.out.println(student);System.out.println(student1);} catch (CloneNotSupportedException e) {e.printStackTrace();}} }

結果

Student{name='pmh', score=Score{score=100}} Student{name='pmh', score=Score{score=100}} Student{name='ZYhf', score=Score{score=99}} Student{name='pmh', score=Score{score=99}}

深拷貝兩種實現方法

1、重寫clone方法來實現深拷貝
1、假設Student有兩個屬性，一個基本數據類型name，一個引用數據類型Socre，我們首先需要讓Score實現cloneable接口，重寫方法clone()

class Score implements Cloneable{int score;public Score(int score) {this.score = score;}public int getScore() {return score;}public void setScore(int score) {this.score = score;}@Overridepublic String toString() {return "Score{" +"score=" + score +'}';}@Overrideprotected Object clone() {Object obj = null;try {obj = super.clone();} catch (CloneNotSupportedException e) {e.printStackTrace();}return obj;} }

2、然后讓Student實現cloneable接口，實現clone方法，通過獲取拷貝的Student實例的Score屬性重新進行一次拷貝

public class Student implements Cloneable {String name;Score score;public Student(String name, Score score) {this.name = name;this.score = score;}public Student() {}public String getName() {return name;}public void setName(String name) {this.name = name;}public Score getScore() {return score;}public void setScore(Score score) {this.score = score;}@Overridepublic String toString() {return "Student{" +"name='" + name + '\'' +", score=" + score +'}';}@Overrideprotected Object clone() {Object obj = null;try {obj = super.clone();} catch (CloneNotSupportedException e) {e.printStackTrace();}Student stu = (Student) obj;stu.score= (Score) stu.getScore().clone();return obj;} }

結果

Student{name='pmh', score=Score{score=100}} Student{name='pmh', score=Score{score=100}} Student{name='ZYhf', score=Score{score=99}} Student{name='pmh', score=Score{score=100}}

雖然層次調用clone方法可以實現深拷貝，但是顯然代碼量實在太大。特別對于屬性數量比較多、層次比較深的類而言，每個類都要重寫clone方法太過繁瑣。
2、通過對象序列化實現深拷貝

class Hobby implements Serializable{private String hobby;public String getHobby() {return hobby;}public void setHobby(String hobby) {this.hobby = hobby;}public Hobby(String hobby) {this.hobby = hobby;}@Overridepublic String toString() {return "Hobby{" +"hobby='" + hobby + '\'' +'}';} } public class Girl implements Serializable{private String name;private Hobby hobby;public String getName() {return name;}public void setName(String name) {this.name = name;}public Hobby getHobby() {return hobby;}public void setHobby(Hobby hobby) {this.hobby = hobby;}public Girl(String name, Hobby hobby) {this.name = name;this.hobby = hobby;}@Overridepublic String toString() {return "Girl{" +"name='" + name + '\'' +", hobby=" + hobby +'}';} } public class CopyWithSerializable {public static void main(String[] args) throws Exception {Hobby hobby = new Hobby("乒乓球");Girl girl1 = new Girl("pmh",hobby);//通過序列化方法實現深拷貝ByteArrayOutputStream bos = new ByteArrayOutputStream();ObjectOutputStream oos = new ObjectOutputStream(bos);oos.writeObject(girl1);oos.flush();ObjectInputStream ois=new ObjectInputStream(new ByteArrayInputStream(bos.toByteArray()));Girl girl2=(Girl)ois.readObject();System.out.println(girl1.toString());System.out.println(girl2.toString());System.out.println();//嘗試修改stu1中的各屬性，觀察stu2的屬性有沒有變化girl1.setName("大傻子");//改變age這個引用類型的成員變量的值hobby.setHobby("羽毛器");girl1.setName("216");System.out.println(girl1.toString());System.out.println(girl2.toString());} }

結果

Girl{name='pmh', hobby=Hobby{hobby='乒乓球'}} Girl{name='pmh', hobby=Hobby{hobby='乒乓球'}} Girl{name='216', hobby=Hobby{hobby='羽毛器'}} Girl{name='pmh', hobby=Hobby{hobby='乒乓球'}}

總結

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