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。