88 lines
2.1 KiB
Markdown
88 lines
2.1 KiB
Markdown
## 享元（Flyweight）
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### Intent
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利用共享的方式来支持大量细粒度的对象，这些对象一部分内部状态是相同的。
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### Class Diagram
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- Flyweight：享元对象
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- IntrinsicState：内部状态，享元对象共享内部状态
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- ExtrinsicState：外部状态，每个享元对象的外部状态不同
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<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/5f5c22d5-9c0e-49e1-b5b0-6cc7032724d4.png"/> </div><br>
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### Implementation
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```java
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public interface Flyweight {
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void doOperation(String extrinsicState);
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}
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```
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```java
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public class ConcreteFlyweight implements Flyweight {
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private String intrinsicState;
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public ConcreteFlyweight(String intrinsicState) {
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this.intrinsicState = intrinsicState;
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}
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@Override
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public void doOperation(String extrinsicState) {
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System.out.println("Object address: " + System.identityHashCode(this));
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System.out.println("IntrinsicState: " + intrinsicState);
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System.out.println("ExtrinsicState: " + extrinsicState);
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}
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}
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```
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```java
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public class FlyweightFactory {
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private HashMap<String, Flyweight> flyweights = new HashMap<>();
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Flyweight getFlyweight(String intrinsicState) {
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if (!flyweights.containsKey(intrinsicState)) {
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Flyweight flyweight = new ConcreteFlyweight(intrinsicState);
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flyweights.put(intrinsicState, flyweight);
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}
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return flyweights.get(intrinsicState);
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}
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}
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```
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```java
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public class Client {
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public static void main(String[] args) {
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FlyweightFactory factory = new FlyweightFactory();
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Flyweight flyweight1 = factory.getFlyweight("aa");
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Flyweight flyweight2 = factory.getFlyweight("aa");
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flyweight1.doOperation("x");
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flyweight2.doOperation("y");
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}
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}
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```
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```html
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Object address: 1163157884
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IntrinsicState: aa
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ExtrinsicState: x
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Object address: 1163157884
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IntrinsicState: aa
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ExtrinsicState: y
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```
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### JDK
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Java 利用缓存来加速大量小对象的访问时间。
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- java.lang.Integer#valueOf(int)
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- java.lang.Boolean#valueOf(boolean)
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- java.lang.Byte#valueOf(byte)
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- java.lang.Character#valueOf(char)
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