英文:
State Design Pattern: How to avoid code duplication when using entry() and exit()?
问题
Situation: 我的状态类(State)具有需要在状态转换时调用的entry()和exit()方法。为确保这一点，我在State类中使用了一个changeState()方法，其中包含必要的过程。它由上下文(Context)在涉及状态机的操作时每次调用。然而，问题在于，每次添加新方法时，我都需要调用state.changeState()，我确信有一种方法可以避免这种代码重复。以下是进一步说明的代码：
class Context {
State state;
void method1() {
state.method1();
state.changeState();
}
void method2() {
state.method2();
state.changeState(); // 代码重复！
}
// 其他方法
}
abstract class State {
Context context;
State next;
void changeState() {
this.exit();
next.entry();
context.setState(next);
}
// 其他必要的方法
}
class ConcreteState extends State {
void method1() {
// 做一些事情
next = AnotherConcreteState;
}
void entry() {/* 做一些事情 */}
void exit() {/* 做一些事情 */}
}
如果我想在Context中添加额外的方法，有什么方法可以避免在新方法中每次调用state.changeState()时出现代码重复？
英文:
Situation: My States have an entry() and exit() method that needs to be called every time when a State transitions. To ensure that, I used a changeState() method in State that contains the necessary procedure. It is called by the Context every time it uses an operation involving the state machine. The problem however, is that I need to call state.changeState() every time when I add a new method and I'm sure there's a way to avoid that code duplication. Below is code for further clarification
class Context {
State state;
void method1() {
state.method1();
state.changeState();
}
void method2() {
state.method2();
state.changeState(); // Code duplication!!
}
abstract class State {
Context context;
State next;
void changeState() {
this.exit();
next.entry();
context.setState(next);
}
// other necessary methods
}
class ConcreteState extends State {
void method1() {
// do something
next = AnotherConcreteState;
}
void entry() {/*do something */};
void exit() {/*do something */};
}
If I want to add additional methods in Context, what can I do to avoid code duplication of calling state.changeState() every time inside the new methods?
答案1
得分: 2
你已经非常接近了。changeState 方法应该属于 Context 类，而不是 State 类。这里有一篇关于这个主题的好文章。请注意，类图中显示 changeState 在 Document（上下文）类中。
为了使代码更清晰，changeState 可以接受 next 状态作为参数，像这样：
class Context {
State state;
void method1() {
state.method1();
}
void changeState(next) {
state.exit();
this.state = next;
state.enter();
}
}
abstract class State {
Context context;
// 其他方法
}
class ConcreteState extends State {
void method1() {
// 做一些事情
context.changeState(AnotherConcreteState);
}
void enter() { /* 做一些事情 */ }
void exit() { /* 做一些事情 */ }
}
现在，当你向 Context 添加更多方法时，不会在 Context 中出现重复。它将如下所示：
class Context {
State state;
void method1() {
state.method1();
}
void method2() {
state.method2();
}
void changeState(next) {
state.exit();
this.state = next;
state.enter();
}
}
abstract class State {
Context context;
// 其他方法
}
class ConcreteState extends State {
void method1() {
// 做一些事情
context.changeState(AnotherConcreteState);
}
void method2() {
// 做一些其他事情
context.changeState(YetAnotherConcreteState);
}
void enter() { /* 做一些事情 */ }
void exit() { /* 做一些事情 */ }
}
英文:
You are very close. The changeState method belongs in the Context class, not the State class. Here's a good article on the topic. Note that the class diagram shows changeState in the Document (context) class.
To make it even cleaner, changeState could take the next state as a parameter. Like this:
class Context {
State state;
void method1() {
state.method1();
}
void changeState(next) {
state.exit();
this.state = next;
state.enter();
}
}
abstract class State {
Context context;
// other methods
}
class ConcreteState extends State {
void method1() {
// do something
context.changeState(AnotherConcreteState);
}
void enter() { /* do something */ }
void exit() { /* do something */ }
}
Now, as you add more methods to Context, there is no duplication in Context. It'd look like this:
class Context {
State state;
void method1() {
state.method1();
}
void method2() {
state.method2();
}
void changeState(next) {
state.exit();
this.state = next;
state.enter();
}
}
abstract class State {
Context context;
// other methods
}
class ConcreteState extends State {
void method1() {
// do something
context.changeState(AnotherConcreteState);
}
void method2() {
// do something else
context.changeState(YetAnotherConcreteState);
}
void enter() { /* do something */ }
void exit() { /* do something */ }
}
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论