设计模式之原型模式

前言

  在项目开发中，会遇到多次实例化同一个类的情况，java中每次实例化一个对象都要执行一次构造函数，如果构造函数的执行时间很长，这个初始化操作就会影响代码运行的效率。设计模式中的原型模式就能很好地避免这种情况.

场景

  简历的复制

原型模式

  用原型实例指定创建对象的种类，并且通过拷贝这些原型创建新的对象。

代码示例

简历类

public class Resume implements Cloneable {

    private String name;

    private String sex;

    private String age;

    private String timeArea;

    private String company;

    public Resume(String name) {
        this.name = name;
    }

    /**
     * 设置个人信息
     *
     * @param sex
     * @param age
     */
    public void setPersonalInfo(String sex, String age) {
        this.sex = sex;
        this.age = age;
    }

    /**
     * 设置工作经历
     *
     * @param timeArea
     * @param company
     */
    public void setWorkExperience(String timeArea, String company) {
        this.timeArea = timeArea;
        this.company = company;
    }

    /**
     * 显示
     */
    public void display() {
        System.out.println(name + " " + sex + " " + age);
        System.out.println("工作经历：" + timeArea + " " + company);
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAge() {
        return age;
    }

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

    public String getTimeArea() {
        return timeArea;
    }

    public void setTimeArea(String timeArea) {
        this.timeArea = timeArea;
    }

    public String getCompany() {
        return company;
    }

    public void setCompany(String company) {
        this.company = company;
    }

    @Override
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }

}

客户端

public static void main(String[] args) throws Exception {
        Resume a = new Resume("大鸟");
        a.setPersonalInfo("男", "29");
        a.setWorkExperience("1998-2000", "XX公司");

        Resume b = (Resume)a.clone();
        b.setWorkExperience("1998-2006", "YY企业");

        Resume c = (Resume)a.clone();
        c.setPersonalInfo("男", "24");

        a.display();
        b.display();
        c.display();
    }

结果显示

深复制与浅复制

浅复制：被复制对象的所有变量都含有与原来对象相同的值，而所有的对其他对象的引用都仍然指向原来的对象。
深复制：把引用对象的变量指向复制过的新对象，而不是原有的被引用的对象。

简历浅复制

工作经历类

public class WorkExperience {

    private String workDate;

    private String company;

    public String getWorkDate() {
        return workDate;
    }

    public void setWorkDate(String workDate) {
        this.workDate = workDate;
    }

    public String getCompany() {
        return company;
    }

    public void setCompany(String company) {
        this.company = company;
    }
}

简历类

public class Resume implements Cloneable {

    private String name;

    private String sex;

    private String age;

    private WorkExperience work;

    public Resume(String name) {
        this.name = name;
        work = new WorkExperience();
    }

    /**
     * 设置个人信息
     *
     * @param sex
     * @param age
     */
    public void setPersonalInfo(String sex, String age) {
        this.sex = sex;
        this.age = age;
    }

    /**
     * 设置工作经历
     *
     * @param workDate
     * @param company
     */
    public void setWorkExperience(String workDate, String company) {
        work.setWorkDate(workDate);
        work.setCompany(company);
    }

    /**
     * 显示
     */
    public void display() {
        System.out.println(name + " " + sex + " " + age);
        System.out.println("工作经历：" + work.getWorkDate() + " " + work.getCompany());
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAge() {
        return age;
    }

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

    @Override
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }

}

客户端

public static void main(String[] args) throws Exception {
        Resume a = new Resume("大鸟");
        a.setPersonalInfo("男", "29");
        a.setWorkExperience("1998-2000", "XX公司");

        Resume b = (Resume)a.clone();
        b.setWorkExperience("1998-2006", "YY企业");

        Resume c = (Resume)a.clone();
        c.setWorkExperience("1998-2003", "ZZ企业");

        a.display();
        b.display();
        c.display();
    }

结果显示

  工作经验使用了引用类型，所以克隆只是复制了引用，对引用的对象还是指向了原来的对象，所以三个引用都是最后一次设置，因为三个引用都指向了同一对象。

简历深复制

工作经历类

public class WorkExperience implements Cloneable {

    private String workDate;

    private String company;

    public String getWorkDate() {
        return workDate;
    }

    public void setWorkDate(String workDate) {
        this.workDate = workDate;
    }

    public String getCompany() {
        return company;
    }

    public void setCompany(String company) {
        this.company = company;
    }

    @Override
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }

}

简历类

public class Resume implements Cloneable {

    private String name;

    private String sex;

    private String age;

    private WorkExperience work;

    public Resume(String name) {
        this.name = name;
        work = new WorkExperience();
    }

    public Resume(WorkExperience work) {
        try {
            this.work = (WorkExperience)work.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
    }

    /**
     * 设置个人信息
     *
     * @param sex
     * @param age
     */
    public void setPersonalInfo(String sex, String age) {
        this.sex = sex;
        this.age = age;
    }

    /**
     * 设置工作经历
     *
     * @param workDate
     * @param company
     */
    public void setWorkExperience(String workDate, String company) {
        work.setWorkDate(workDate);
        work.setCompany(company);
    }

    /**
     * 显示
     */
    public void display() {
        System.out.println(name + " " + sex + " " + age);
        System.out.println("工作经历：" + work.getWorkDate() + " " + work.getCompany());
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAge() {
        return age;
    }

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

    @Override
    public Object clone() throws CloneNotSupportedException {

        Resume obj = new Resume(this.work);
        obj.name = this.name;
        obj.sex = this.sex;
        obj.age = this.age;
        return obj;
    }

}

客户端

public static void main(String[] args) throws Exception {
        Resume a = new Resume("大鸟");
        a.setPersonalInfo("男", "29");
        a.setWorkExperience("1998-2000", "XX公司");

        Resume b = (Resume)a.clone();
        b.setWorkExperience("1998-2006", "YY企业");

        Resume c = (Resume)a.clone();
        c.setWorkExperience("1998-2003", "ZZ企业");

        a.display();
        b.display();
        c.display();
    }

运行结果

参考资料
[1]: 大话设计模式 程杰著 清华大学出版社