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1 /*
2  * @(#)Formattable.java 1.3 04/04/21
3  *
4  * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5  * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6  */
7
8 package java.util;
9
10 import java.io.IOException JavaDoc;
11
12 /**
13  * The <tt>Formattable</tt> interface must be implemented by any class that
14  * needs to perform custom formatting using the <tt>'s'</tt> conversion
15  * specifier of {@link java.util.Formatter}. This interface allows basic
16  * control for formatting arbitrary objects.
17  *
18  * For example, the following class prints out different representations of a
19  * stock's name depending on the flags and length constraints:
20  *
21  * <blockquote><pre>
22  * import java.nio.CharBuffer;
23  * import java.util.Formatter;
24  * import java.util.Formattable;
25  * import java.util.Locale;
26  * import static java.util.FormattableFlags.*;
27  *
28  * ...
29  *
30  * public class StockName implements Formattable {
31  * private String symbol, companyName, frenchCompanyName;
32  * public StockName(String symbol, String companyName,
33  * String frenchCompanyName) {
34  * ...
35  * }
36  *
37  * ...
38  *
39  * public void formatTo(Formatter fmt, int f, int width, int precision) {
40  * StringBuilder sb = new StringBuilder();
41  *
42  * // decide form of name
43  * String name = companyName;
44  * if (fmt.locale().equals(Locale.FRANCE))
45  * name = frenchCompanyName;
46  * boolean alternate = (f & ALTERNATE) == ALTERNATE;
47  * boolean usesymbol = alternate || (precision != -1 && precision < 10);
48  * String out = (usesymbol ? symbol : name);
49  *
50  * // apply precision
51  * if (precision == -1 || out.length() < precision) {
52  * // write it all
53  * sb.append(out);
54  * } else {
55  * sb.append(out.substring(0, precision - 1)).append('*');
56  * }
57  *
58  * // apply width and justification
59  * int len = sb.length();
60  * if (len < width)
61  * for (int i = 0; i < width - len; i++)
62  * if ((f & LEFT_JUSTIFY) == LEFT_JUSTIFY)
63  * sb.append(' ');
64  * else
65  * sb.insert(0, ' ');
66  *
67  * fmt.format(sb.toString());
68  * }
69  *
70  * public String toString() {
71  * return String.format("%s - %s", symbol, companyName);
72  * }
73  * }
74  * </pre></blockquote>
75  *
76  * <p> When used in conjunction with the {@link java.util.Formatter}, the above
77  * class produces the following output for various format strings.
78  *
79  * <blockquote><pre>
80  * Formatter fmt = new Formatter();
81  * StockName sn = new StockName("HUGE", "Huge Fruit, Inc.",
82  * "Fruit Titanesque, Inc.");
83  * fmt.format("%s", sn); // -> "Huge Fruit, Inc."
84  * fmt.format("%s", sn.toString()); // -> "HUGE - Huge Fruit, Inc."
85  * fmt.format("%#s", sn); // -> "HUGE"
86  * fmt.format("%-10.8s", sn); // -> "HUGE "
87  * fmt.format("%.12s", sn); // -> "Huge Fruit,*"
88  * fmt.format(Locale.FRANCE, "%25s", sn); // -> " Fruit Titanesque, Inc."
89  * </pre></blockquote>
90  *
91  * <p> Formattables are not necessarily safe for multithreaded access. Thread
92  * safety is optional and may be enforced by classes that extend and implement
93  * this interface.
94  *
95  * <p> Unless otherwise specified, passing a <tt>null</tt> argument to
96  * any method in this interface will cause a {@link
97  * NullPointerException} to be thrown.
98  *
99  * @version 1.3, 04/21/04
100  * @since 1.5
101  */
102 public interface Formattable {
103
104     /**
105      * Formats the object using the provided {@link Formatter formatter}.
106      *
107      * @param formatter
108      * The {@link Formatter formatter}. Implementing classes may call
109      * {@link Formatter#out() formatter.out()} or {@link
110      * Formatter#locale() formatter.locale()} to obtain the {@link
111      * Appendable} or {@link Locale} used by this
112      * <tt>formatter</tt> respectively.
113      *
114      * @param flags
115      * The flags modify the output format. The value is interpreted as
116      * a bitmask. Any combination of the following flags may be set:
117      * {@link FormattableFlags#LEFT_JUSTIFY}, {@link
118      * FormattableFlags#UPPERCASE}, and {@link
119      * FormattableFlags#ALTERNATE}. If no flags are set, the default
120      * formatting of the implementing class will apply.
121      *
122      * @param width
123      * The minimum number of characters to be written to the output.
124      * If the length of the converted value is less than the
125      * <tt>width</tt> then the output will be padded by
126      * <tt>'&nbsp;&nbsp;'</tt> until the total number of characters
127      * equals width. The padding is at the beginning by default. If
128      * the {@link FormattableFlags#LEFT_JUSTIFY} flag is set then the
129      * padding will be at the end. If <tt>width</tt> is <tt>-1</tt>
130      * then there is no minimum.
131      *
132      * @param precision
133      * The maximum number of characters to be written to the output.
134      * The precision is applied before the width, thus the output will
135      * be truncated to <tt>precision</tt> characters even if the
136      * <tt>width</tt> is greater than the <tt>precision</tt>. If
137      * <tt>precision</tt> is <tt>-1</tt> then there is no explicit
138      * limit on the number of characters.
139      *
140      * @throws IllegalFormatException
141      * If any of the parameters are invalid. For specification of all
142      * possible formatting errors, see the <a
143      * HREF="../util/Formatter.html#detail">Details</a> section of the
144      * formatter class specification.
145      */
146     void formatTo(Formatter JavaDoc formatter, int flags, int width, int precision);
147 }
148
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