java设计模式--原型模式

 

  原型模式:用原型实例指定创建对象的种类,并通过拷贝这些原型创建新的对象。通俗来说就是克隆一个对象,而且不用知道创建对象的细节,然后对这个对象进行自定义操作。首先,我们先看一下下面的这个例子。

//公司类
public
class Company { private String level; private Long workYears; public String getLevel() { return level; } public void setLevel(String level) { this.level = level; } public Long getWorkYears() { return workYears; } public void setWorkYears(Long workYears) { this.workYears = workYears; } } //实现Cloneable接口的People类(原型实例) public class People implements Cloneable { private String name; private Long age; private String gender; //公司属性,没有实现Cloneable接口 private Company company; public String getName() { return name; } public People() { //在初始People类的同时创建company实例 this.company = new Company(); } public void setName(String name) { this.name = name; } public Long getAge() { return age; } public void setAge(Long age) { this.age = age; } public String getGender() { return gender; } public void setGender(String gender) { this.gender = gender; } public Company getCompany() { return company; } public void setCompany(String level,Long workYears) { //给company的属性赋值 this.company.setLevel(level); this.company.setWorkYears(workYears); } //Clone()方法,clone people类 public Object Clone() { Object clone = null; try { clone = super.clone(); } catch (CloneNotSupportedException e) { e.printStackTrace(); } return (People) clone; } public void show() { System.out.println("name:" + name + ",age:" + age + ",gender" + gender); System.out.println("name:" + name + ",level:" + company.getLevel() + ",workYears:" + company.getWorkYears()); } } public class Test { public static void main(String[] args) {
     //原型实例对象 People people
= new People(); people.setName("zhangsan"); people.setAge(23L); people.setGender("man"); people.setCompany("A7",3L); //克隆对象1,修改age,gender属性 People clone1 = (People)people.Clone(); clone1.setAge(25L); clone1.setGender("woman"); //克隆对象2,修改age,company属性 People clone2 = (People)people.Clone(); clone2.setAge(26L); clone2.setCompany("A8",4L); people.show(); clone1.show(); clone2.show(); } }

得到的结果为:

name:zhangsan,age:23,genderman
name:zhangsan,level:A8,workYears:4

name:zhangsan,age:25,genderwoman
name:zhangsan,level:A8,workYears:4

name:zhangsan,age:26,genderman
name:zhangsan,level:A8,workYears:4

  我们可以看到值类型的字段都会拷贝一份新的出来,对他们修改也不会对被克隆对象的值进行修改,但是如果字段是引用类型,则拷贝引用,但不复制引用的对象,这样的话如果我们对引用类型的字段company进行修改就会导致显示的永远是最后一次修改的值,因为拷贝出的三个引用指向一个对象,这就是浅拷贝。

 

  那么如果我们想把引用类型的字段也拷贝一份出来呢,那么我们就需要把引用类型也实现Cloneable接口,并重写Clone()方法,并且把引用类型的属性再拷贝一遍,代码如下:

public class Company implements Cloneable{

    private String level;
    private Long workYears;

    public String getLevel() {
        return level;
    }

    public void setLevel(String level) {
        this.level = level;
    }

    public Long getWorkYears() {
        return workYears;
    }

    public void setWorkYears(Long workYears) {
        this.workYears = workYears;
    }

    //Clone()方法,clone company类
    public Object Clone() {
        Object clone = null;
        try {
            clone = super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return clone;
    }
}

//实现Cloneable接口的People类
public class People implements Cloneable {
    private String name;
    private Long age;
    private String gender;
    private Company company;

    public String getName() {
        return name;
    }

    public void setName(String name) {

        this.name = name;
    }

    public People() {
        //在给People赋name的同时创建company实例
        this.company = new Company();
    }

    public People(Company company) {
        this.company = (Company) company.Clone();
    }

    public Long getAge() {
        return age;
    }

    public void setAge(Long age) {
        this.age = age;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public Company getCompany() {
        return company;
    }

    public void setCompany(String level, Long workYears) {
        //给company的属性赋值
        this.company.setLevel(level);
        this.company.setWorkYears(workYears);
    }

    //Clone()方法,clone people类
    public Object Clone() {
        Object object = null;
        try {
            object = super.clone();
        //把引用类型company再拷贝一遍 ((People)object).company
= (Company) this.company.Clone(); } catch (CloneNotSupportedException exception) { throw new RuntimeException(exception); } return object; } public void show() { System.out.println("name:" + name + ",age:" + age + ",gender" + gender); System.out.println("name:" + name + ",level:" + company.getLevel() + ",workYears:" + company.getWorkYears()); } }

结果为:

name:zhangsan,age:23,genderman
name:zhangsan,level:A7,workYears:3

name:zhangsan,age:25,genderwoman
name:zhangsan,level:A7,workYears:3

name:zhangsan,age:26,genderman
name:zhangsan,level:A8,workYears:4

  我们可以看到对复制出的对象中的引用对象company赋值时,并没有改变原型对象,因为引用对象的变量指向了新的克隆出的对象,这就是深拷贝。

总结:原型模式的优点就是可以快速创建对象,比直接new一个对象再进行赋值的操作性能要好,缺点就是每个类都得实现克隆方法,当有多层引用时,需要考虑是否会造成引用死循环。

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