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    1   /*
    2    * Copyright (c) 2003, 2004, Oracle and/or its affiliates. All rights reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Oracle designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
   25   
   26   package java.util;
   27   
   28   import java.io.IOException;
   29   
   30   /**
   31    * The <tt>Formattable</tt> interface must be implemented by any class that
   32    * needs to perform custom formatting using the <tt>'s'</tt> conversion
   33    * specifier of {@link java.util.Formatter}.  This interface allows basic
   34    * control for formatting arbitrary objects.
   35    *
   36    * For example, the following class prints out different representations of a
   37    * stock's name depending on the flags and length constraints:
   38    *
   39    * <blockquote><pre>
   40    *   import java.nio.CharBuffer;
   41    *   import java.util.Formatter;
   42    *   import java.util.Formattable;
   43    *   import java.util.Locale;
   44    *   import static java.util.FormattableFlags.*;
   45    *
   46    *  ...
   47    *
   48    *   public class StockName implements Formattable {
   49    *       private String symbol, companyName, frenchCompanyName;
   50    *       public StockName(String symbol, String companyName,
   51    *                        String frenchCompanyName) {
   52    *           ...
   53    *       }
   54    *
   55    *       ...
   56    *
   57    *       public void formatTo(Formatter fmt, int f, int width, int precision) {
   58    *           StringBuilder sb = new StringBuilder();
   59    *
   60    *           // decide form of name
   61    *           String name = companyName;
   62    *           if (fmt.locale().equals(Locale.FRANCE))
   63    *               name = frenchCompanyName;
   64    *           boolean alternate = (f & ALTERNATE) == ALTERNATE;
   65    *           boolean usesymbol = alternate || (precision != -1 && precision < 10);
   66    *           String out = (usesymbol ? symbol : name);
   67    *
   68    *           // apply precision
   69    *           if (precision == -1 || out.length() < precision) {
   70    *               // write it all
   71    *               sb.append(out);
   72    *           } else {
   73    *               sb.append(out.substring(0, precision - 1)).append('*');
   74    *           }
   75    *
   76    *           // apply width and justification
   77    *           int len = sb.length();
   78    *           if (len < width)
   79    *               for (int i = 0; i < width - len; i++)
   80    *                   if ((f & LEFT_JUSTIFY) == LEFT_JUSTIFY)
   81    *                       sb.append(' ');
   82    *                   else
   83    *                       sb.insert(0, ' ');
   84    *
   85    *           fmt.format(sb.toString());
   86    *       }
   87    *
   88    *       public String toString() {
   89    *           return String.format("%s - %s", symbol, companyName);
   90    *       }
   91    *   }
   92    * </pre></blockquote>
   93    *
   94    * <p> When used in conjunction with the {@link java.util.Formatter}, the above
   95    * class produces the following output for various format strings.
   96    *
   97    * <blockquote><pre>
   98    *   Formatter fmt = new Formatter();
   99    *   StockName sn = new StockName("HUGE", "Huge Fruit, Inc.",
  100    *                                "Fruit Titanesque, Inc.");
  101    *   fmt.format("%s", sn);                   //   -> "Huge Fruit, Inc."
  102    *   fmt.format("%s", sn.toString());        //   -> "HUGE - Huge Fruit, Inc."
  103    *   fmt.format("%#s", sn);                  //   -> "HUGE"
  104    *   fmt.format("%-10.8s", sn);              //   -> "HUGE      "
  105    *   fmt.format("%.12s", sn);                //   -> "Huge Fruit,*"
  106    *   fmt.format(Locale.FRANCE, "%25s", sn);  //   -> "   Fruit Titanesque, Inc."
  107    * </pre></blockquote>
  108    *
  109    * <p> Formattables are not necessarily safe for multithreaded access.  Thread
  110    * safety is optional and may be enforced by classes that extend and implement
  111    * this interface.
  112    *
  113    * <p> Unless otherwise specified, passing a <tt>null</tt> argument to
  114    * any method in this interface will cause a {@link
  115    * NullPointerException} to be thrown.
  116    *
  117    * @since  1.5
  118    */
  119   public interface Formattable {
  120   
  121       /**
  122        * Formats the object using the provided {@link Formatter formatter}.
  123        *
  124        * @param  formatter
  125        *         The {@link Formatter formatter}.  Implementing classes may call
  126        *         {@link Formatter#out() formatter.out()} or {@link
  127        *         Formatter#locale() formatter.locale()} to obtain the {@link
  128        *         Appendable} or {@link Locale} used by this
  129        *         <tt>formatter</tt> respectively.
  130        *
  131        * @param  flags
  132        *         The flags modify the output format.  The value is interpreted as
  133        *         a bitmask.  Any combination of the following flags may be set:
  134        *         {@link FormattableFlags#LEFT_JUSTIFY}, {@link
  135        *         FormattableFlags#UPPERCASE}, and {@link
  136        *         FormattableFlags#ALTERNATE}.  If no flags are set, the default
  137        *         formatting of the implementing class will apply.
  138        *
  139        * @param  width
  140        *         The minimum number of characters to be written to the output.
  141        *         If the length of the converted value is less than the
  142        *         <tt>width</tt> then the output will be padded by
  143        *         <tt>'&nbsp;&nbsp;'</tt> until the total number of characters
  144        *         equals width.  The padding is at the beginning by default.  If
  145        *         the {@link FormattableFlags#LEFT_JUSTIFY} flag is set then the
  146        *         padding will be at the end.  If <tt>width</tt> is <tt>-1</tt>
  147        *         then there is no minimum.
  148        *
  149        * @param  precision
  150        *         The maximum number of characters to be written to the output.
  151        *         The precision is applied before the width, thus the output will
  152        *         be truncated to <tt>precision</tt> characters even if the
  153        *         <tt>width</tt> is greater than the <tt>precision</tt>.  If
  154        *         <tt>precision</tt> is <tt>-1</tt> then there is no explicit
  155        *         limit on the number of characters.
  156        *
  157        * @throws  IllegalFormatException
  158        *          If any of the parameters are invalid.  For specification of all
  159        *          possible formatting errors, see the <a
  160        *          href="../util/Formatter.html#detail">Details</a> section of the
  161        *          formatter class specification.
  162        */
  163       void formatTo(Formatter formatter, int flags, int width, int precision);
  164   }

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