com.hazelcast.util.StateMachine Maven / Gradle / Ivy
/*
* Copyright (c) 2008-2015, Hazelcast, Inc. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.hazelcast.util;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import static com.hazelcast.util.ValidationUtil.checkNotNull;
import static com.hazelcast.util.ValidationUtil.checkState;
/**
* Simple state machine using an Enum as possible states.
*
* @param
*/
public class StateMachine> {
private Map> transitions = new HashMap>();
private T currentState;
public StateMachine(T initialState) {
currentState = initialState;
}
public static > StateMachine of(T initialState) {
return new StateMachine(initialState);
}
/**
* Add a valid transition from one state to one or more states
**/
public StateMachine withTransition(T from, T to, T... moreTo) {
transitions.put(from, EnumSet.of(to, moreTo));
return this;
}
/**
* Transition to next state
* @throws IllegalStateException if transition is not allowed
*/
public StateMachine next(T nextState) throws IllegalStateException {
Set allowed = transitions.get(currentState);
checkNotNull(allowed, "No transitions from state " + currentState);
checkState(allowed.contains(nextState), "Transition not allowed from state " + currentState + " to " + nextState);
currentState = nextState;
return this;
}
/**
* Transition to next state if not already there
*/
public void nextOrStay(T nextState) {
if (!is(nextState)) {
next(nextState);
}
}
/**
* Check if current state is one of given states
*/
public boolean is(T state, T ... otherStates) {
return EnumSet.of(state, otherStates).contains(currentState);
}
@Override
public String toString() {
return "StateMachine{state=" + currentState + "}";
}
}