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定义：享元模式（Flyweight Pattern）又称为轻量级模式，是对象池的一种实现．类似于线程池，线程池可以避免不停的创建和销毁多个对象，消耗性能．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

宗旨：共享细粒度对象，将多个对同一对象的访问集中起来

属于结构型模式

适用场景

常常应用于系统低层的开发，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

享元模式扩展

内部状态 :不可改变的,不随环境的变化而变化

外部状态 :可以改变的

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

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

例子

一般用法

key做为一个类别,在多个对象中抽出来相似的做为一个类别,当参数进行传递

public interface IFlyweight {
       void operation(String extrinsicState);}

public class ConcreteFlyweight implements IFlyweight{
       private String intrinsicState;    public ConcreteFlyweight(String intrinsicState){
           this.intrinsicState = intrinsicState;    }    @Override    public void operation(String extrinsicState) {
           System.out.println("Object address: " + System.identityHashCode(this));        System.out.println("IntrinsicState: " + this.intrinsicState);        System.out.println("ExtrinsicState: " + extrinsicState);    }}

public class FlyweightFactory {
       private static Map
   
     pool = new HashMap<>();    public static IFlyweight getFlyweight(String intrinsicState){
           if(!pool.containsKey(intrinsicState)){
               IFlyweight flyweight = new ConcreteFlyweight(intrinsicState);            pool.put(intrinsicState,flyweight);        }        return pool.get(intrinsicState);    }}
   

public class Test {
       public static void main(String[] args) {
           String[] str = {
   "student","teacher","police"};        for(int i = 0; i < 100;i ++) {
               IFlyweight iFlyweight = FlyweightFactory.getFlyweight(str[i%3]);            iFlyweight.operation("你在干啥");        }    }}

数据库连接池

public class ConnectionPool {
       private Vector
   
     pool;    private int poolSize = 100;    private String url = "jdbc:mysql://localhost:3306/test";    private String username = "root";    private String password = "root";    private String driverClassName = "com.mysql.jdbc.Driver";    public ConnectionPool(){
           pool = new Vector
    
     (poolSize);        try{
               Class.forName(driverClassName);            for(int i = 0; i < poolSize; i ++){
                   Connection connection = DriverManager.getConnection(url, username, password);                pool.add(connection);            }        }catch (Exception e){
               e.printStackTrace();        }    }    public synchronized Connection getConnection(){
           if(pool.size()>0){
               Connection conn = pool.get(0);            pool.remove(conn);            return conn;        }        return null;    }    public synchronized void release(Connection conn){
           pool.add(conn);    }}
    
   

public class Test {
       public static void main(String[] args) {
           ConnectionPool pool = new ConnectionPool();        Connection connection = pool.getConnection();        System.out.println(connection);    }}

jdk中享元模式使用

String 中常量池

public class StringTest {
       public static void main(String[] args) {
           String s1 = "hello";        String s2 = "hello";        System.out.println(s1 == s2);//true        String s3 = "he" + "llo";        System.out.println(s1 == s3);//true        String s4 = "he" + new String("llo");        System.out.println(s1 == s4);//false        String s5 = new String("hello");        System.out.println(s1 == s5);//false        String s6 = s5.intern();        System.out.println(s1 == s6);//true        String s7 = "h";        String s8 = "ello";        String s9 = s7 + s8;        System.out.println(s1 == s9);//false        String s10 = s9.intern();        System.out.println(s1 == s10);    }}

Interger 中缓存-128 到127的缓存池

public class IntegerTest {
       public static void main(String[] args) {
           Integer a = Integer.valueOf(100);        Integer b = 100;        System.out.println(a == b);//true        Integer c = Integer.valueOf(1000);        Integer d = 1000;        System.out.println(c == d);//false    }}

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