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Apache HttpComponents Core (blocking I/O)
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/*
 * ====================================================================
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * .
 *
 */

package org.apache.http;

import org.apache.http.annotation.Contract;
import org.apache.http.annotation.ThreadingBehavior;

/**
 * Represents an HTTP version. HTTP uses a "major.minor" numbering
 * scheme to indicate versions of the protocol.
 * 
 * The version of an HTTP message is indicated by an HTTP-Version field
 * in the first line of the message.
 * 
 *  *     HTTP-Version   = "HTTP" "/" 1*DIGIT "." 1*DIGIT
 * 
 *
 * @since 4.0
 */
@Contract(threading = ThreadingBehavior.IMMUTABLE)
public final class HttpVersion extends ProtocolVersion {

    private static final long serialVersionUID = -5856653513894415344L;

    /** The protocol name. */
    public static final String HTTP = "HTTP";

    /** HTTP protocol version 0.9 */
    public static final HttpVersion HTTP_0_9 = new HttpVersion(0, 9);

    /** HTTP protocol version 1.0 */
    public static final HttpVersion HTTP_1_0 = new HttpVersion(1, 0);

    /** HTTP protocol version 1.1 */
    public static final HttpVersion HTTP_1_1 = new HttpVersion(1, 1);


    /**
     * Create an HTTP protocol version designator.
     *
     * @param major   the major version number of the HTTP protocol
     * @param minor   the minor version number of the HTTP protocol
     *
     * @throws IllegalArgumentException if either major or minor version number is negative
     */
    public HttpVersion(final int major, final int minor) {
        super(HTTP, major, minor);
    }


    /**
     * Obtains a specific HTTP version.
     *
     * @param major     the major version
     * @param minor     the minor version
     *
     * @return  an instance of {@link HttpVersion} with the argument version
     */
    @Override
    public ProtocolVersion forVersion(final int major, final int minor) {

        if ((major == this.major) && (minor == this.minor)) {
            return this;
        }

        if (major == 1) {
            if (minor == 0) {
                return HTTP_1_0;
            }
            if (minor == 1) {
                return HTTP_1_1;
            }
        }
        if ((major == 0) && (minor == 9)) {
            return HTTP_0_9;
        }

        // argument checking is done in the constructor
        return new HttpVersion(major, minor);
    }

}