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 * {@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>' '</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 }