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/*
* Copyright (C) 2019 The Android Open Source Project
*
* 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.android.internal.net.utils;
/**
* SimpleStateMachine provides a minimal, synchronous state machine framework.
*
* <p>This state machine is of limited functionality, but sufficient for implementation of simple
* protocols. Due to the limited functionality, it is also easy to read and maintain.
*
* SimpleStateMachine defaults to the null state. Implementers should immediately transition
* to their default state when instantiated.
*
* @param <T> The input message type.
* @param <R> The result type. For SimpleStateMachines without a return value, use {@link
* java.lang.Void}
*/
public abstract class SimpleStateMachine<T, R> {
protected final SimpleState mNullState =
new SimpleState() {
public R process(T msg) {
throw new IllegalStateException("Process called on null state");
}
};
protected SimpleState mState = mNullState;
// Non-static to allow for compiler verification of T, R from SimpleStateMachine
protected abstract class SimpleState {
public abstract R process(T msg);
}
/**
* Processes the given message based on the current {@link SimpleState}
*
* @param msg The message to be processed by the current state
* @return The result of the processing by the current state
*/
public R process(T msg) {
return mState.process(msg);
}
/**
* Transitions to a new state
*
* @param newState The {@link SimpleState} that the {@link SimpleStateMachine} should
* transition to
* @throws IllegalArgumentException if newState is null
*/
protected void transitionTo(SimpleState newState) {
if (newState == null) {
throw new IllegalArgumentException("SimpleState value must be non-null.");
}
mState = newState;
}
/**
* Transitions to a new state, and lets the new state process the given message
*
* @param newState The {@link SimpleState} that the {@link SimpleStateMachine} should transition
* to. This state will immediately be requested to process the given message.
* @param msg The message that should be processed by the new state
* @return The result of the processing by the new state
* @throws IllegalArgumentException if newState is null
*/
protected R transitionAndProcess(SimpleState newState, T msg) {
transitionTo(newState);
return mState.process(msg);
}
}
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