享元模式 — 共享重用

最聪明的人是最不愿浪费时间的人。 ——但丁

1、定义

享元模式 （Flyweight Pattern），享元模式是以共享的模式来支持大量细粒度对象的复用。

2、组成角色

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享元模式包含的角色列举如下：

• 抽象享元角色（Flyweight）：一般是一个具体的抽象类，同时定义了对象的外部状态和内部状态的接口或实现；
• 具体享元角色（ConcreteFlyweight）：具体的一个产品类，实现了抽象享元角色中定义的接口，该角色需要注意的是内部状态的处理应该与环境无关；
• 享元工厂（FlyweightFactory）：该角色指责一般比较清晰，就是一个池工厂，提供池对象和获取池中对象的方法

3、使用实例

抽象享元角色类

public abstract class ExamInfo {
    private String student;
    private String subject;
    public ExamInfo(String subject) {
        this.subject = subject;
    }
    public String getStudent() {
        return student;
    }
    public void setStudent(String student) {
        this.student = student;
    }
    public String getSubject() {
        return subject;
    }
    public void setSubject(String subject) {
        this.subject = subject;
    }
    public abstract void operate(); 
}

具体享元角色类

public class ConcreteExamInfo extends ExamInfo{
    public ConcreteExamInfo(String subject) {
        super(subject);
    }
    @Override
    public void operate() {
        System.out.println(this.getStudent()+"正在考"+this.getSubject());
    }
}

享元工厂类

public class ExamInfoFactory {
    private  static Map<String,ExamInfo> examInfoMap = new HashMap<>();
    public static ExamInfo getExamInfo(String subject){
        ExamInfo examInfo;
        if(examInfoMap.containsKey(subject)){
            System.out.println("直接从池中获取..." + subject);
            examInfo = examInfoMap.get(subject);
        }else {
            examInfo = new ConcreteExamInfo(subject);
            examInfoMap.put(subject,examInfo);
            System.out.println("建立对象，并放到池中..." + subject);
        }
        return examInfo;
    }
}

客户端类

public class Main {
    public static void main(String[] args) {
        ExamInfo examInfo = ExamInfoFactory.getExamInfo("数学");
        examInfo.setStudent("小红");
        examInfo.operate();
        examInfo = ExamInfoFactory.getExamInfo("数学");
        examInfo.setStudent("小明");
        examInfo.operate();
        examInfo = ExamInfoFactory.getExamInfo("数学");
        examInfo.setStudent("小李");
        examInfo.operate();
        examInfo = ExamInfoFactory.getExamInfo("语文");
        examInfo.setStudent("小红");
        examInfo.operate();
        examInfo = ExamInfoFactory.getExamInfo("语文");
        examInfo.setStudent("小明");
        examInfo.operate();
        examInfo = ExamInfoFactory.getExamInfo("语文");
        examInfo.setStudent("小李");
        examInfo.operate();
    }
}

测试结果打印

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4、总结

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5、代码下载