Clone()方法深度剖析

拷贝，顾名思义就是复制，分配新的内存，产生新的对象，与new关键字类似。然而，拷贝中存在部分隐匿的差别，需要我们细细查看

// 学士：姓名 年龄 信息
public class Bachelor {
    private String name;
    private int age;
    private Info info;
    
    public Bachelor(String name,int age,Info info){
        this.name = name;
        this.age = age;
        this.info = info;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Info getInfo() {
        return info;
    }
    public void setInfo(Info info) {
        this.info = info;
    }   
}
// 信息：技能　项目　
class Info{
    private String level;
    private Project project;
    
    public Info(String level,Project project){
        this.level = level;
        this.project = project;
    }
    public Project getProject() {
        return project;
    }
    public void setProject(Project project) {
        this.project = project;
    }
}
// 项目：项目名称
class Project{
    private String projectName;
    
    public Project(String projectName){
        this.projectName = projectName;
    }
}

1. 引用拷贝
   不同引用指向相同地址，并不分配新的内存空间；

    // 测试代码
    Project project = new Project("myApp");
    Info info = new Info("A",project);
    Bachelor bachelorOne = new Bachelor("Cheng",23,info);
    
    Bachelor bachelorTwo = bachelorOne;
    System.out.println(bachelorOne);
    System.out.println(bachelorTwo);

// 打印出相同的地址
javaBasic.Bachelor@15db9742
javaBasic.Bachelor@15db9742

2. 对象拷贝

// 实现Cloneable接口，复写clone()方法
public class Bachelor implements Cloneable{
    @Override
    protected Object clone() throws CloneNotSupportedException {
        Bachelor newBachelor = (Bachelor) super.clone();
        return newBachelor;
    }
}

    // 测试代码
    Project project = new Project("myApp");
    Info info = new Info("A",project);
    Bachelor bachelorOne = new Bachelor("Cheng",23,info);

    Bachelor bachelorTwo = (Bachelor) bachelorOne.clone();
    System.out.println(bachelorOne);
    System.out.println(bachelorTwo);
    System.out.println(bachelorOne.getName() == bachelorTwo.getName());

// 打印出不同地址，且name引用相同
javaBasic.Bachelor@15db9742
javaBasic.Bachelor@6d06d69c
true

• 浅拷贝
  如上面测试代码，分配新的内存，创建新对象，但是name属性却存在相同的引用，即拷贝主对象，却不拷贝主对象里面的对象；
  如何实现name属性的拷贝呢？

    // 重新生成name对象
    @Override
    protected Object clone() throws CloneNotSupportedException {
        Bachelor newBachelor = (Bachelor) super.clone();
        newBachelor.name = new String(this.name);
        return newBachelor;
    }

按照此种逻辑，info对象也是浅拷贝，如何实现主对象中对象的拷贝呢？

// 类实现Cloneable接口，复写clone方法
// 在clone()方法中，实现主对象内对象的重新生成
public class Bachelor implements Cloneable{
    @Override
    protected Object clone() throws CloneNotSupportedException {
        Bachelor newBachelor = (Bachelor) super.clone();
        newBachelor.name = new String(this.name);
        newBachelor.info = (Info) this.info.clone();
        return newBachelor;
    }
}

class Info implements Cloneable{
    @Override
    protected Object clone() throws CloneNotSupportedException {
        Info newInfo = (Info) super.clone();
        // 将level属性和project方法均重新生成
        newInfo.level = new String(this.level);
        newInfo.project = (Project) this.project.clone();
        return newInfo;
    }

class Project implements Cloneable{
    @Override
    protected Object clone() throws CloneNotSupportedException {
        // TODO Auto-generated method stub
        return (Project) super.clone();
    }
}

// 测试代码
    Project project = new Project("myApp");
    Info info = new Info("A",project);
    Bachelor bachelorOne = new Bachelor("Cheng",23,info);
        
    Bachelor bachelorTwo = (Bachelor) bachelorOne.clone();
    System.out.println(bachelorOne);
    System.out.println(bachelorTwo);
    System.out.println(bachelorOne.getName() == bachelorTwo.getName());
    System.out.println(bachelorTwo.getInfo() == bachelorOne.getInfo());
    System.out.println(bachelorTwo.getInfo().getProject() == bachelorOne.getInfo().getProject());

// 实现主对象内部所有对象的拷贝
javaBasic.Bachelor@15db9742
javaBasic.Bachelor@6d06d69c
false
false
false

• 深拷贝
  实现主对象全部结构的拷贝，包括主对象中的对象；