设计模式之原型模式讲解

原型模式本身就是一种很简单的模式，在Java当中，由于内置了Cloneable 接口，就使得原型模式在Java中的实现变得非常简单。UML图如下：

我们来举一个生成新员工的例子来帮助大家理解。

import java.util.Date;
public class Employee implements Cloneable {
    private String id;
    private String name;
    private Date hireDate;
    private transient Address address; // 注意：transient关键字表示此字段不参与序列化，这里假设地址不需要深拷贝
    public Employee(String id, String name, Date hireDate, Address address) {
        this.id = id;
        this.name = name;
        this.hireDate = (Date) hireDate.clone(); // 防止原始hireDate被修改
        this.address = address;
    }
    public String getId() {
        return id;
    }
    public String getName() {
        return name;
    }
    public Date getHireDate() {
        return (Date) hireDate.clone(); // 返回原始hireDate的副本
    }
    public Address getAddress() {
        return address;
    }
    // 重写Object的clone方法，实现浅拷贝
    @Override
    public Employee clone() throws CloneNotSupportedException {
        Employee clonedEmployee = (Employee) super.clone();
        // 如果有引用类型字段需要深拷贝，需要在这里进行额外处理
        // 例如，如果Address也需要深拷贝，可以添加如下代码：
        // clonedEmployee.address = address.clone();
        return clonedEmployee;
    }
}
class Address implements Cloneable {
    private String street;
    private String city;
    private String country;
    public Address(String street, String city, String country) {
        this.street = street;
        this.city = city;
        this.country = country;
    }
    // 提供Address的克隆方法实现深拷贝
    public Address clone() {
        return new Address(street, city, country);
    }
    // ... getters and setters ...
}
public class PrototypeDemo {
    public static void main(String[] args) {
        try {
            // 创建原始员工对象
            Address address = new Address("123 Main St", "Anytown", "USA");
            Employee original = new Employee("001", "John Doe", new Date(), address);
            // 使用clone方法创建新员工对象
            Employee cloned = original.clone();
            // 修改克隆对象的属性，验证克隆是否成功
            cloned.setName("Jane Doe");
            cloned.getAddress().setCity("Another City");
            System.out.println("Original Employee:");
            System.out.println("ID: " + original.getId());
            System.out.println("Name: " + original.getName());
            System.out.println("Hire Date: " + original.getHireDate());
            System.out.println("Address: " + original.getAddress());
            System.out.println("\nCloned Employee:");
            System.out.println("ID: " + cloned.getId());
            System.out.println("Name: " + cloned.getName());
            System.out.println("Hire Date: " + cloned.getHireDate());
            System.out.println("Address: " + cloned.getAddress());
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
    }
}