标签:享元 String innerState 模式 System println 设计模式 public
享元模式
定义
- 使用共享对象有效地支持大量的细粒度对象,类似线程池,本质是缓存共享对象
举例
通用结构
- 抽象享元角色Flyweight:享元对象接口,定义对象的外部状态和内部状态
- 具体享元角色Concrete Flyweight:享元对象实现,该角色的内部状态处理应于外部状态无关
- 享元工厂Flyweight Factory: 负责管理享元对象池和创建享元对象
public interface IFlyweight {
void operation(String existState);
}
public class ConcreteFlyweight implements IFlyweight{
private final String innerState;
public ConcreteFlyweight(String innerState){
this.innerState = innerState;
}
@Override
public void operation(String existState) {
System.out.println(String.format("Object Address: %s, innerState: %s, existState: %s",
System.identityHashCode(this),this.innerState,existState));
}
}
public class FlyweightFactory {
private static final Map<String,IFlyweight> pool = new ConcurrentHashMap<>();
public static IFlyweight getFlyweight(String innerState){
if (!pool.containsKey(innerState)){
pool.put(innerState,new ConcreteFlyweight(innerState));
}
return pool.get(innerState);
}
}
public class Test {
@Test
public void testGetFlyweight(){
IFlyweight flyweight = FlyweightFactory.getFlyweight("a");
IFlyweight flyweight2 = FlyweightFactory.getFlyweight("a");
IFlyweight flyweight3 = FlyweightFactory.getFlyweight("b");
flyweight.operation("1");
flyweight2.operation("2");
flyweight3.operation("3");
}
}
源码应用
JDK中的String:
JVM的字符串常量保存于字符串常量池中,JDK 7.0版本由永生代迁至堆中。
如果以字面量的形式创建String,JVM编译器就会把它保存在字符串常量池中,常量池中有且只有一份相同的字面量,如果有其他相同的字面量,则会返回这个引用
public static void main(String[] args) {
String s1 = "hello";
String s2 = "hello";
String s3 = "hel" + "lo";
String s4 = "hel";
String s5 = "lo";
String s6 = s4 + s5;
final String s7 = "hel";
final String s8 = "lo";
String s9 = s7 + s8;
String s10 = new String("hello");
String s11 = s10.intern();
System.out.println(s1 == s2);
System.out.println(s1 == s3);
System.out.println(s1 == s6);
System.out.println(s1 == s9);
System.out.println(s1 == s10);
System.out.println(s1 == s11);
}
JDK中的Interger:
Interger内部缓存了一个-128 至127的常量池,valueOf方法会返回在这期间的值
public static void main(String[] args) {
Integer a = Integer.valueOf(100);
Integer b = 100;
Integer c = Integer.valueOf(128);
Integer d = 128;
System.out.println(a == b);
System.out.println(c == d);
}
个人心得
- 适合需要大量创建对象的场景,降低系统内存消耗
- 需要关注对象的内外部状态、线程安全等问题,复杂度增加
标签:享元,String,innerState,模式,System,println,设计模式,public 来源: https://blog.csdn.net/weixin_47313214/article/details/120450808
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