Java状态和策略设计模式的区别

Java开发人员必须清楚地了解 Core Java应用程序中状态和策略设计模式之间的区别，以便正确使用它们。

• State 和 Strategy 设计模式虽然结构相似，都基于 Open Closed 设计原则，代表 SOLID 设计原则中的“O”，但它们的意图完全不同。
• Java的策略设计模式用于封装一组相关的算法，为客户端提供运行时灵活性。客户端可以在运行时选择任何算法，而无需更改使用 Strategy 对象的 Context 类。
• 策略模式的一些流行示例是编写代码，它使用算法，例如加密、压缩或排序算法。

现在可以清楚地看到 Strategy 和 State 模式之间的区别，它们的意图是不同的。状态模式帮助对象管理状态，而策略模式允许客户端选择不同的行为。另一个不容易看到的区别是，谁推动了行为的改变。

在策略模式的情况下，它是客户端，它提供了与上下文不同的策略，在状态模式中，状态转换由上下文或状态本身管理。此外，如果您在 State 对象本身中管理状态转换，则它必须持有上下文的引用，以便它可以调用setState()方法来更改 Context 的当前状态。自动售货机是最受欢迎的例子之一。

到目前为止，我们注意到状态和策略在结构上是相似的，它们的意图是不同的。因此，以下是Java状态和策略设计模式之间的主要主要区别，它们在它们的类中看起来都很相似，它们都执行开放封闭设计原则并封装行为。使用 Strategy 设计模式，封装算法或策略，在运行时提供给 Context，可能作为参数或组合对象，并使用 State Pattern 管理Java的状态转换。

STATE PATTERN	STRATEGY PATTERN
In-State pattern, an individual state can contain the reference of Context, to implement state transitions.	But Strategies doesn’t contain the reference of Context, where they are used.
State encapsulate state of an Object.	While Strategy Pattern encapsulates an algorithm or strategy.
State pattern helps a class to exhibit different behaviors in a different state.	Strategy Pattern encapsulates a set of related algorithms and allows the client to use interchangeable behaviors through composition and delegation at runtime.
The state is part of the context object itself, and over time, the context object transitions from one State to another.	It can be passed as a parameter to there the Object which uses them e.g. Collections.sort() accepts a Comparator, which is a strategy.
State Pattern defines the “what” and “when” part of an Object. Example: What can an object when it’s in a certain state.	Strategy pattern defines the “How” part of an Object. Example: How a Sorting object sorts data.
Order of State transition is well-defined in State pattern.	There is no such requirement for a Strategy pattern. The client is free to choose any Strategy implementation of his choice.
Change in State can be done by Context or State object itself.	Change in Strategy is done by the Client.
Some common examples of Strategy Patterns are encapsulating algorithms e.g. sorting algorithms, encryption algorithms, or compression algorithms.	On the other hand, recognizing the use of State design patterns is pretty easy.
If you see, your code needs to use different kinds of related algorithms, then think of using a Strategy pattern.	If you need to manage state and state transition, without lots of nested conditional statements, state pattern is the pattern to use.