state pattern
时间: 2023-10-11 17:06:19 浏览: 34
状态模式(State Pattern)是一种行为型设计模式,它允许对象在其内部状态改变时改变它的行为。在状态模式中,将对象的状态封装成一个独立的对象,使得对象的行为可以根据其内部状态改变而改变,而不需要在对象自身内部维护大量的条件判断语句。
状态模式的核心思想是将状态作为一个对象来表示,并将每个状态的行为封装在该状态对象之中。当对象的状态发生改变时,它会自动切换到对应的状态对象,从而改变其行为。这样可以使得对象更加灵活和可扩展,而且可以降低对象之间的耦合度。
状态模式通常涉及到以下几个角色:
1. Context(环境):它是拥有多种状态的对象,可以请求状态对象来改变其行为。
2. State(状态):它是状态模式的核心,用于封装对象的状态和行为,并在状态发生改变时更新对象的状态。
3. ConcreteState(具体状态):它是状态的具体实现,包含了状态所对应的行为。在状态切换时,它会将对象的状态切换到新的状态。
状态模式的优点在于它能够将对象的状态和行为分离,使得对象的设计更加清晰,同时也能够避免大量的条件判断语句。同时,状态模式还具有良好的扩展性和可维护性,可以方便地增加新的状态和行为。
相关问题
2)Explain the difference between State pattern and Decorator pattern.5)Give the code required for the classes introduced in question 2), focusing on the code for a method selectState() which changes the value that is being adjusted from years to months. Make it clear in which classes the code is to be found. Assume the existence of other methods that are needed such as getMonthSetUpState().
2) The State pattern is a behavioral design pattern that allows an object to alter its behavior when its internal state changes. This pattern involves creating state objects that represent various states of the object and a context object whose behavior varies as its state object changes.
On the other hand, the Decorator pattern is a structural design pattern that allows behavior to be added to an individual object, either statically or dynamically, without affecting the behavior of other objects from the same class. This pattern involves creating decorator objects that wrap the original object and provide additional functionality while keeping the original object's interface intact.
5) Here is the code for the classes introduced in question 2), focusing on the code for a method selectState() which changes the value that is being adjusted from years to months:
```java
// Context interface
interface Account {
void selectState(State state);
void deposit(double amount);
void withdraw(double amount);
double getBalance();
}
// Concrete Context class
class SavingsAccount implements Account {
private State state;
private double balance;
public SavingsAccount() {
this.state = new YearsSetUpState(); // default state
this.balance = 0.0;
}
@Override
public void selectState(State state) {
this.state = state;
}
@Override
public void deposit(double amount) {
this.balance += state.adjustDeposit(amount);
}
@Override
public void withdraw(double amount) {
this.balance -= state.adjustWithdrawal(amount);
}
@Override
public double getBalance() {
return this.balance;
}
// Other methods needed
public State getMonthSetUpState() {
return new MonthsSetUpState();
}
}
// State interface
interface State {
double adjustDeposit(double deposit);
double adjustWithdrawal(double withdrawal);
}
// Concrete State classes
class YearsSetUpState implements State {
@Override
public double adjustDeposit(double deposit) {
return deposit;
}
@Override
public double adjustWithdrawal(double withdrawal) {
return withdrawal;
}
}
class MonthsSetUpState implements State {
@Override
public double adjustDeposit(double deposit) {
return deposit / 12;
}
@Override
public double adjustWithdrawal(double withdrawal) {
return withdrawal / 12;
}
}
```
In the above code, the `Account` interface represents the context object, while the `State` interface represents the state objects. The `SavingsAccount` class is a concrete context class that implements the `Account` interface and keeps track of the current state object. The `YearsSetUpState` and `MonthsSetUpState` classes are concrete state classes that implement the `State` interface and provide specific behavior for each state.
The `selectState()` method is implemented in the `SavingsAccount` class and allows the current state object to be changed. The `deposit()` and `withdraw()` methods use the current state object to adjust the deposit and withdrawal amounts accordingly. The `getBalance()` method returns the current balance of the account.
The `getMonthSetUpState()` method is also implemented in the `SavingsAccount` class and returns a new `MonthsSetUpState` object, which can be used to change the current state object to adjust the deposit and withdrawal amounts from years to months.
vue 中pattern获取值
在Vue中获取pattern的值可以通过以下几种方式实现。首先,在Vue的模板中可以使用{{ this.$store.state.pattern }}来获取vuex中的数据。这种方式适用于在模板中直接展示pattern的值。
另外,可以使用this.$refs来获取input元素的值。首先需要给input标签加上ref属性,比如ref="inputRef",然后可以通过this.$refs.inputRef.value来获取input的值。这种方式适用于需要在JavaScript代码中获取input的值的情况。
最后,如果你使用了Vuex来管理数据,你可以在Vuex中定义state对象,并在mutations中定义setPattern方法来修改pattern的值。然后在需要获取pattern的地方,可以使用this.$store.state.pattern来获取它的值。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
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