行为模式：State（状态）

The state interface and two implementations. The state's method has a reference to the context object and is able to change its state.

interface Statelike {

/**
* Writer method for the state name.
* @param STATE_CONTEXT
* @param NAME
*/
void writeName(final StateContext STATE_CONTEXT, final String NAME);

}

class StateA implements Statelike {
/* (non-Javadoc)
* @see state.Statelike#writeName(state.StateContext, java.lang.String)
*/
@Override
public void writeName(final StateContext STATE_CONTEXT, final String NAME) {
System.out.println(NAME.toLowerCase());
STATE_CONTEXT.setState(new StateB());
}

}

class StateB implements Statelike {
/** State counter */
private int count = 0;

/* (non-Javadoc)
* @see state.Statelike#writeName(state.StateContext, java.lang.String)
*/
@Override
public void writeName(final StateContext STATE_CONTEXT, final String NAME) {
System.out.println(NAME.toUpperCase());
// Change state after StateB's writeName() gets invoked twice
if(++count > 1) {
STATE_CONTEXT.setState(new StateA());
}
}

}

The context class has a state variable that it instantiates in an initial state, in this case

StateA

. In its method, it uses the corresponding methods of the state
object.

public class StateContext {
private Statelike myState;
/**
* Standard constructor
*/
public StateContext() {
setState(new StateA());
}

/**
* Setter method for the state.
* Normally only called by classes implementing the State interface.
* @param NEW_STATE
*/
public void setState(final Statelike NEW_STATE) {
myState = NEW_STATE;
}

/**
* Writer method
* @param NAME
*/
public void writeName(final String NAME) {
myState.writeName(this, NAME);
}
}

The test below shows also the usage:

public class TestClientState {
public static void main(String[] args) {
final StateContext SC = new StateContext();

SC.writeName("Monday");
SC.writeName("Tuesday");
SC.writeName("Wednesday");
SC.writeName("Thursday");
SC.writeName("Friday");
SC.writeName("Saturday");
SC.writeName("Sunday");
}
}

According to the above code, the output of main() from TestClientState should be:

monday
TUESDAY
WEDNESDAY
thursday
FRIDAY
SATURDAY
sunday