享元模式

1.定义：提供了减少对象数量从而改善应用所需的对象结构的方式；
　　　   运用共享技术有效地支持大量细粒度的对象。

2.类型：结构型

3.适用场景：常常应用于底层的开发，以便解决系统的性能问题；
　　　　　   系统有大量相似对象、需要缓冲池的场景。

4.优点：减少对象的创建，降低内存中对象的数量，降低系统的内存，提高效率；
　　　   减少内存之外的其他资源占用。

5.缺点：关注内/外部状态、关注线程安全问题；使系统、程序的逻辑复杂化。

6.扩展：内部状态、外部状态

7.相关设计模式：代理模式、单例模式

8.实例目录package

9.实例UML类图

10.代码

package com.geely.design.pattern.structural.flyweight;

public interface Employee {
    void report();
}

package com.geely.design.pattern.structural.flyweight;

public class Manager implements Employee {
    private String title = "部门经理";
    private String department;
    private String reportContent;

    public Manager(String department) {
        this.department = department;
    }

    public void setReportContent(String reportContent) {
        this.reportContent = reportContent;
    }

    @Override
    public void report() {
        System.out.println(reportContent);
    }
}

package com.geely.design.pattern.structural.flyweight;

import java.util.HashMap;
import java.util.Map;

public class EmployeeFactory {
    private static final Map<String,Employee> EMPLOYEE_MAP = new HashMap<>();

    public static Employee getManager(String department){
        Manager manager = (Manager) EMPLOYEE_MAP.get(department);
        if(manager == null){
            manager = new Manager(department);
            System.out.println("创建部门经理：" + department);
            String reportContent = department + "部门汇报：此次报告的内容是。。。";
            manager.setReportContent(reportContent);
            System.out.println("创建报告：" + reportContent);
            EMPLOYEE_MAP.put(department,manager);
        }
        return manager;
    }
}

package com.geely.design.pattern.structural.flyweight;

public class Test {
    private static final String[] departments = {"RD", "QA", "PM", "BD"};
    public static void main(String[] args) {
        for (int i = 0; i < 10; i++){
            String department = departments[(int)(Math.random()*departments.length)];
            Manager manager = (Manager) EmployeeFactory.getManager(department);
            manager.report();
        }

        Integer a = Integer.valueOf(100);//new Integer(100);
        Integer b = 100;
        Integer c = Integer.valueOf(1000);//new Integer(1000);
        Integer d = 1000;
        System.out.println("a==b:"+(a==b));
        System.out.println("c==d:"+(c==d));
    }
}