Java example source code file (ReadableInstant.java)

This example Java source code file (ReadableInstant.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

chronology, comparable, datetimezone, instant, readableinstant, string

The ReadableInstant.java Java example source code

/*
 *  Copyright 2001-2009 Stephen Colebourne
 *
 *  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.joda.time;

/**
 * Defines an instant in the datetime continuum.
 * This interface expresses the datetime as milliseconds from 1970-01-01T00:00:00Z.
 * <p>
 * The implementation of this interface may be mutable or immutable.
 * This interface only gives access to retrieve data, never to change it.
 * <p>
 * Methods in your application should be defined using <code>ReadableInstant
 * as a parameter if the method only wants to read the instant without needing to know
 * the specific datetime fields.
 * <p>
 * The {@code compareTo} method is no longer defined in this class in version 2.0.
 * Instead, the definition is simply inherited from the {@code Comparable} interface.
 * This approach is necessary to preserve binary compatibility.
 * The definition of the comparison is ascending order by millisecond instant.
 * Implementors are recommended to extend {@code AbstractInstant} instead of this interface.
 *
 * @author Stephen Colebourne
 * @since 1.0
 */
public interface ReadableInstant extends Comparable<ReadableInstant> {

    /**
     * Get the value as the number of milliseconds since
     * the epoch, 1970-01-01T00:00:00Z.
     *
     * @return the value as milliseconds
     */
    long getMillis();

    /**
     * Gets the chronology of the instant.
     * <p>
     * The {@link Chronology} provides conversion from the millisecond
     * value to meaningful fields in a particular calendar system.
     * 
     * @return the Chronology, never null
     */
    Chronology getChronology();

    /**
     * Gets the time zone of the instant from the chronology.
     * 
     * @return the DateTimeZone that the instant is using, never null
     */
    DateTimeZone getZone();

    /**
     * Get the value of one of the fields of a datetime.
     * <p>
     * This method uses the chronology of the instant to obtain the value.
     *
     * @param type  a field type, usually obtained from DateTimeFieldType, not null
     * @return the value of that field
     * @throws IllegalArgumentException if the field type is null
     */
    int get(DateTimeFieldType type);

    /**
     * Checks whether the field type specified is supported by this implementation.
     *
     * @param field  the field type to check, may be null which returns false
     * @return true if the field is supported
     */
    boolean isSupported(DateTimeFieldType field);

    //-----------------------------------------------------------------------
    /**
     * Get the value as a simple immutable <code>Instant object.
     * <p>
     * This can be useful if you don't trust the implementation
     * of the interface to be well-behaved, or to get a guaranteed
     * immutable object.
     *
     * @return the value as an <code>Instant object
     */
    Instant toInstant();

    //-----------------------------------------------------------------------
    // Method is no longer defined here as that would break generic backwards compatibility
//    /**
//     * Compares this object with the specified object for ascending
//     * millisecond instant order. This ordering is inconsistent with
//     * equals, as it ignores the Chronology.
//     * <p>
//     * All ReadableInstant instances are accepted.
//     *
//     * @param readableInstant  a readable instant to check against
//     * @return negative value if this is less, 0 if equal, or positive value if greater
//     * @throws NullPointerException if the object is null
//     * @throws ClassCastException if the object type is not supported
//     */
//    int compareTo(ReadableInstant readableInstant);

    //-----------------------------------------------------------------------
    /**
     * Is this instant equal to the instant passed in
     * comparing solely by millisecond.
     *
     * @param instant  an instant to check against, null means now
     * @return true if the instant is equal to the instant passed in
     */
    boolean isEqual(ReadableInstant instant);

    /**
     * Is this instant after the instant passed in
     * comparing solely by millisecond.
     *
     * @param instant  an instant to check against, null means now
     * @return true if the instant is after the instant passed in
     */
    boolean isAfter(ReadableInstant instant);

    /**
     * Is this instant before the instant passed in
     * comparing solely by millisecond.
     *
     * @param instant  an instant to check against, null means now
     * @return true if the instant is before the instant passed in
     */
    boolean isBefore(ReadableInstant instant);

    //-----------------------------------------------------------------------
    /**
     * Compares this object with the specified object for equality based
     * on the millisecond instant and the Chronology. All ReadableInstant
     * instances are accepted.
     * <p>
     * To compare two instants for absolute time (ie. UTC milliseconds 
     * ignoring the chronology), use {@link #isEqual(ReadableInstant)} or
     * {@link #compareTo(Object)}.
     *
     * @param readableInstant  a readable instant to check against
     * @return true if millisecond and chronology are equal, false if
     *  not or the instant is null or of an incorrect type
     */
    boolean equals(Object readableInstant);

    /**
     * Gets a hash code for the instant that is compatible with the 
     * equals method.
     * <p>
     * The formula used must be as follows:
     * <pre>
     * ((int) (getMillis() ^ (getMillis() >>> 32))) +
     * (getChronology().hashCode())
     * </pre>
     *
     * @return a hash code as defined above
     */
    int hashCode();

    //-----------------------------------------------------------------------
    /**
     * Get the value as a String in a recognisable ISO8601 format.
     * <p>
     * The string output is in ISO8601 format to enable the String
     * constructor to correctly parse it.
     *
     * @return the value as an ISO8601 string
     */
    String toString();

}