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      */
formatTo(Formatter formatter, int flags, int width, int precision)163     void formatTo(Formatter formatter, int flags, int width, int precision);
164 }
165