src/java.base/share/classes/java/text/FieldPosition.java

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/*
 * (C) Copyright Taligent, Inc. 1996 - All Rights Reserved
 * (C) Copyright IBM Corp. 1996 - All Rights Reserved
 *
 *   The original version of this source code and documentation is copyrighted
 * and owned by Taligent, Inc., a wholly-owned subsidiary of IBM. These
 * materials are provided under terms of a License Agreement between Taligent
 * and Sun. This technology is protected by multiple US and International
 * patents. This notice and attribution to Taligent may not be removed.
 *   Taligent is a registered trademark of Taligent, Inc.
 *
 */

package java.text;

import java.util.Objects;

/**
 * {@code FieldPosition} is a simple class used by {@code Format}
 * and its subclasses to identify fields in formatted output. Fields can
 * be identified in two ways:
 * <ul>
 *  <li>By an integer constant, whose names typically end with
 *      {@code _FIELD}. The constants are defined in the various
 *      subclasses of {@code Format}.
 *  <li>By a {@code Format.Field} constant, see {@code ERA_FIELD}
 *      and its friends in {@code DateFormat} for an example.
 * </ul>
 * <p>
 * {@code FieldPosition} keeps track of the position of the
 * field within the formatted output with two indices: the index
 * of the first character of the field and the index of the last
 * character of the field.
 *
 * <p>
 * One version of the {@code format} method in the various
 * {@code Format} classes requires a {@code FieldPosition}
 * object as an argument. You use this {@code format} method
 * to perform partial formatting or to get information about the
 * formatted output (such as the position of a field).
 *
 * <p>
 * If you are interested in the positions of all attributes in the
 * formatted string use the {@code Format} method
 * {@code formatToCharacterIterator}.
 *
 * @author      Mark Davis
 * @since 1.1
 * @see         java.text.Format
 */
public class FieldPosition {

    /**
     * Input: Desired field to determine start and end offsets for.
     * The meaning depends on the subclass of Format.
     */
    int field = 0;

    /**
     * Output: End offset of field in text.
     * If the field does not occur in the text, 0 is returned.
     */
    int endIndex = 0;

    /**
     * Output: Start offset of field in text.
     * If the field does not occur in the text, 0 is returned.
     */
    int beginIndex = 0;

    /**
     * Desired field this FieldPosition is for.
     */
    private Format.Field attribute;

    /**
     * Creates a FieldPosition object for the given field.  Fields are
     * identified by constants, whose names typically end with _FIELD,
     * in the various subclasses of Format.
     *
     * @param field the field identifier
     * @see java.text.NumberFormat#INTEGER_FIELD
     * @see java.text.NumberFormat#FRACTION_FIELD
     * @see java.text.DateFormat#YEAR_FIELD
     * @see java.text.DateFormat#MONTH_FIELD
     */
    public FieldPosition(int field) {
        this.field = field;
    }

    /**
     * Creates a FieldPosition object for the given field constant. Fields are
     * identified by constants defined in the various {@code Format}
     * subclasses. This is equivalent to calling
     * {@code new FieldPosition(attribute, -1)}.
     *
     * @param attribute Format.Field constant identifying a field
     * @since 1.4
     */
    public FieldPosition(Format.Field attribute) {
        this(attribute, -1);
    }

    /**
     * Creates a {@code FieldPosition} object for the given field.
     * The field is identified by an attribute constant from one of the
     * {@code Field} subclasses as well as an integer field ID
     * defined by the {@code Format} subclasses. {@code Format}
     * subclasses that are aware of {@code Field} should give precedence
     * to {@code attribute} and ignore {@code fieldID} if
     * {@code attribute} is not null. However, older {@code Format}
     * subclasses may not be aware of {@code Field} and rely on
     * {@code fieldID}. If the field has no corresponding integer
     * constant, {@code fieldID} should be -1.
     *
     * @param attribute Format.Field constant identifying a field
     * @param fieldID integer constant identifying a field
     * @since 1.4
     */
    public FieldPosition(Format.Field attribute, int fieldID) {
        this.attribute = attribute;
        this.field = fieldID;
    }

    /**
     * Returns the field identifier as an attribute constant
     * from one of the {@code Field} subclasses. May return null if
     * the field is specified only by an integer field ID.
     *
     * @return Identifier for the field
     * @since 1.4
     */
    public Format.Field getFieldAttribute() {
        return attribute;
    }

    /**
     * Retrieves the field identifier.
     *
     * @return the field identifier
     */
    public int getField() {
        return field;
    }

    /**
     * Retrieves the index of the first character in the requested field.
     *
     * @return the begin index
     */
    public int getBeginIndex() {
        return beginIndex;
    }

    /**
     * Retrieves the index of the character following the last character in the
     * requested field.
     *
     * @return the end index
     */
    public int getEndIndex() {
        return endIndex;
    }

    /**
     * Sets the begin index.  For use by subclasses of Format.
     *
     * @param bi the begin index
     * @since 1.2
     */
    public void setBeginIndex(int bi) {
        beginIndex = bi;
    }

    /**
     * Sets the end index.  For use by subclasses of Format.
     *
     * @param ei the end index
     * @since 1.2
     */
    public void setEndIndex(int ei) {
        endIndex = ei;
    }

    /**
     * Returns a {@code Format.FieldDelegate} instance that is associated
     * with the FieldPosition. When the delegate is notified of the same
     * field the FieldPosition is associated with, the begin/end will be
     * adjusted.
     */
    Format.FieldDelegate getFieldDelegate() {
        return new Delegate();
    }

    /**
     * Overrides equals
     */
    @Override
    public boolean equals(Object obj)
    {
        if (!(obj instanceof FieldPosition other))
            return false;
        if (!Objects.equals(attribute, other.attribute))
            return false;
        return (beginIndex == other.beginIndex
            && endIndex == other.endIndex
            && field == other.field);
    }

    /**
     * {@return a hash code for this FieldPosition}
     */
    @Override
    public int hashCode() {
        return (field << 24) | (beginIndex << 16) | endIndex;
    }

    /**
     * Return a string representation of this FieldPosition.
     * @return  a string representation of this object
     */
    public String toString() {
        return getClass().getName() +
            "[field=" + field + ",attribute=" + attribute +
            ",beginIndex=" + beginIndex +
            ",endIndex=" + endIndex + ']';
    }


    /**
     * Return true if the receiver wants a {@code Format.Field} value and
     * {@code attribute} is equal to it.
     */
    private boolean matchesField(Format.Field attribute) {
        if (this.attribute != null) {
            return this.attribute.equals(attribute);
        }
        return false;
    }

    /**
     * Return true if the receiver wants a {@code Format.Field} value and
     * {@code attribute} is equal to it, or true if the receiver
     * represents an integer constant and {@code field} equals it.
     */
    private boolean matchesField(Format.Field attribute, int field) {
        if (this.attribute != null) {
            return this.attribute.equals(attribute);
        }
        return (field == this.field);
    }


    /**
     * An implementation of FieldDelegate that will adjust the begin/end
     * of the FieldPosition if the arguments match the field of
     * the FieldPosition.
     */
    private class Delegate implements Format.FieldDelegate {
        /**
         * Indicates whether the field has been  encountered before. If this
         * is true, and {@code formatted} is invoked, the begin/end
         * are not updated.
         */
        private boolean encounteredField;

        public void formatted(Format.Field attr, Object value, int start,
                              int end, Format.StringBuf buffer) {
            if (!encounteredField && matchesField(attr)) {
                setBeginIndex(start);
                setEndIndex(end);
                encounteredField = (start != end);
            }
        }

        public void formatted(int fieldID, Format.Field attr, Object value,
                              int start, int end, Format.StringBuf buffer) {
            if (!encounteredField && matchesField(attr, fieldID)) {
                setBeginIndex(start);
                setEndIndex(end);
                encounteredField = (start != end);
            }
        }
    }
}