State.java

/*
 * Copyright (c) OSGi Alliance (2002, 2013). 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 org.osgi.util.measurement;

/**
 * Groups a state name, value and timestamp.
 * 
 * <p>
 * The state itself is represented as an integer and the time is measured in
 * milliseconds since midnight, January 1, 1970 UTC.
 * 
 * <p>
 * A {@code State} object is immutable so that it may be easily shared.
 * 
 * @Immutable
 * @author $Id: 415613f3925b2d69f27517c1ef2fc389507b62dc $
 */
public class State {
	private final int		value;
	private final long		time;
	private final String	name;

	/**
	 * Create a new {@code State} object.
	 * 
	 * @param value The value of the state.
	 * @param name The name of the state.
	 * @param time The time measured in milliseconds since midnight, January 1,
	 *        1970 UTC.
	 */
	public State(int value, String name, long time) {
		this.value = value;
		this.name = name;
		this.time = time;
	}

	/**
	 * Create a new {@code State} object with a time of 0.
	 * 
	 * @param value The value of the state.
	 * @param name The name of the state.
	 */
	public State(int value, String name) {
		this(value, name, 0);
	}

	/**
	 * Returns the value of this {@code State}.
	 * 
	 * @return The value of this {@code State} object.
	 */
	public final int getValue() {
		return value;
	}

	/**
	 * Returns the time with which this {@code State} was created.
	 * 
	 * @return The time with which this {@code State} was created. The time is
	 *         measured in milliseconds since midnight, January 1, 1970 UTC.
	 */
	public final long getTime() {
		return time;
	}

	/**
	 * Returns the name of this {@code State}.
	 * 
	 * @return The name of this {@code State} object.
	 */
	public final String getName() {
		return name;
	}

	/**
	 * Returns a {@code String} object representing this object.
	 * 
	 * @return a {@code String} object representing this object.
	 */
	public String toString() {
		StringBuffer sb = new StringBuffer();
		sb.append(value);
		if (name != null) {
			sb.append(" \"");
			sb.append(name);
			sb.append("\"");
		}
		return sb.toString();
	}

	/**
	 * Returns a hash code value for this object.
	 * 
	 * @return A hash code value for this object.
	 */
	public int hashCode() {
		int hash = 31 * 17 + value;
		if (name != null) {
			hash = 31 * hash + name.hashCode();
		}
		return hash;
	}

	/**
	 * Return whether the specified object is equal to this object. Two
	 * {@code State} objects are equal if they have same value and name.
	 * 
	 * @param obj The object to compare with this object.
	 * @return {@code true} if this object is equal to the specified object;
	 *         {@code false} otherwise.
	 */
	public boolean equals(Object obj) {
		if (this == obj) {
			return true;
		}
		if (!(obj instanceof State)) {
			return false;
		}
		State that = (State) obj;
		if (value != that.value) {
			return false;
		}
		if (name == that.name) {
			return true;
		}
		if (name == null) {
			return false;
		}
		return name.equals(that.name);
	}
}