[Java101 基礎篇] 三張圖搞懂 Shallow Copy 以及 Deep Copy

前言
有些時候，我們會需要將資料(物件) 覆製一份，
方便獨立操作 ~ 卻發現結果跟想像的不一樣。

讓我們從程式碼來做個說明~

Sample Code

public class Person {
    Name name;
    Address address;
    Person(Person p) {
         this.name = p.name;
         this.address = p.address;
    }
    // 其它省略…
}

class Address {
    String road;
    String city;
    String zipcode;
}

class Name {
    String firstName;
    String lastName;
}

public class Person {

Name name;

Address address;

Person(Person p) {

this.name = p.name;

this.address = p.address;

}

// 其它省略…

}

class Address {

String road;

String city;

String zipcode;

}

class Name {

String firstName;

String lastName;

}

一個正常的物件 Person p = new Person();

Shadow Copy

Person mother = new Person(new Name(), new Address());
Person son  = new Person(mother);   //將上一個物件傳到目前物件的建構子

1 2	Person mother = new Person(new Name(), new Address()); Person son = new Person(mother); //將上一個物件傳到目前物件的建構子

java101_referenceCopy — **有二個參考點(References)指到同一份資料**

Deep Copy

public class Person {
    private Name name;
    private Address address;
    public Person(Person otherPerson) {
         this.name    =  new Name(otherPerson.name);        //產生新物件
         this.address =  new Address(otherPerson.address);  //產生新物件
    }
}

public class Person {

private Name name;

private Address address;

public Person(Person otherPerson) {

this.name = new Name(otherPerson.name); //產生新物件

this.address = new Address(otherPerson.address); //產生新物件

}

//承接上面的程式碼
Person mother = new Person(new Name(), new Address()); //有mother自己的資料
Person son  = new Person(mother);   //將上一個物件的資料覆製一份，會另產生一份獨立的。

//承接上面的程式碼

Person mother = new Person(new Name(), new Address()); //有mother自己的資料

Person son = new Person(mother); //將上一個物件的資料覆製一份，會另產生一份獨立的。

對了~

對參考點的概念(Reference) 還不是很清楚?!
對建構子的運用還想更進一步嗎?! 可以參考我們提供的教育訓練。

參考資料:
https://dzone.com/articles/java-copy-shallow-vs-deep-in-which-you-will-swim

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