1 /*

     2  * Copyright (c) 2003, 2013, 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  * {@code

    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  * }

    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  * {@code

    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  * }

   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 }