这段话基本上是说，您可以将状态编码为单独的类 - 然后实例类型就是“状态”，这些类不需要任何实例变量，因为它们的类型编码了您需要的所有信息。
例如，假设我想有三种状态“打开”、“激活”和“关闭”。我可能定义以下类：
abstract class State {};
class Open extends State {
public Open() {}
}
class Active extends State {
public Active() {}
}
class Closed extends State {
public Closed() {}
}
--
另一个选项——我猜测这就是GOF文本中所暗示的与享元模式相结合的组合——是创建一个状态类，其中包含一堆静态成员（每个状态对应一个静态成员），然后可以共享使用。
public class State {
private string name;
private State(String name) {
this.name = name;
}
public final static State OPEN = new State("Open");
public final static State ACTIVE = new State("Active");
public final static State CLOSED = new State("Closed");
}
class SomeStateMachine;
class AbstractState {
// abstract baseclass for all state-classes
void input(const std::string & data, SomeStateMachine & caller) = 0;
}
class FinalState : public AbstractState {
FinalState * getInstance(); // always returns same instance
}
class InitialState : public AbstractState {
public:
InitialState * getInstance(); // always returns same instance
void input(const std::string & data, SomeStateMachine & caller) {
std::cout << data << std::endl;
caller.m_State = FinalState::getInstance();
}
}
class SomeStateMachine {
public:
SomeStateMachine() : m_State(InitialState::getInstance())
void input(const std::string & data) {
m_State->input(data, *this);
}
private:
friend class InitialState;
AbstractState * m_State;
};