Java tutorial
/* * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.util; import java.io.IOException; /** * The {@code Formattable} interface must be implemented by any class that * needs to perform custom formatting using the {@code 's'} conversion * specifier of {@link java.util.Formatter}. This interface allows basic * control for formatting arbitrary objects. * * For example, the following class prints out different representations of a * stock's name depending on the flags and length constraints: * * <pre> {@code * import java.nio.CharBuffer; * import java.util.Formatter; * import java.util.Formattable; * import java.util.Locale; * import static java.util.FormattableFlags.*; * * ... * * public class StockName implements Formattable { * private String symbol, companyName, frenchCompanyName; * public StockName(String symbol, String companyName, * String frenchCompanyName) { * ... * } * * ... * * public void formatTo(Formatter fmt, int f, int width, int precision) { * StringBuilder sb = new StringBuilder(); * * // decide form of name * String name = companyName; * if (fmt.locale().equals(Locale.FRANCE)) * name = frenchCompanyName; * boolean alternate = (f & ALTERNATE) == ALTERNATE; * boolean usesymbol = alternate || (precision != -1 && precision < 10); * String out = (usesymbol ? symbol : name); * * // apply precision * if (precision == -1 || out.length() < precision) { * // write it all * sb.append(out); * } else { * sb.append(out.substring(0, precision - 1)).append('*'); * } * * // apply width and justification * int len = sb.length(); * if (len < width) * for (int i = 0; i < width - len; i++) * if ((f & LEFT_JUSTIFY) == LEFT_JUSTIFY) * sb.append(' '); * else * sb.insert(0, ' '); * * fmt.format(sb.toString()); * } * * public String toString() { * return String.format("%s - %s", symbol, companyName); * } * } * }</pre> * * <p> When used in conjunction with the {@link java.util.Formatter}, the above * class produces the following output for various format strings. * * <pre> {@code * Formatter fmt = new Formatter(); * StockName sn = new StockName("HUGE", "Huge Fruit, Inc.", * "Fruit Titanesque, Inc."); * fmt.format("%s", sn); // -> "Huge Fruit, Inc." * fmt.format("%s", sn.toString()); // -> "HUGE - Huge Fruit, Inc." * fmt.format("%#s", sn); // -> "HUGE" * fmt.format("%-10.8s", sn); // -> "HUGE " * fmt.format("%.12s", sn); // -> "Huge Fruit,*" * fmt.format(Locale.FRANCE, "%25s", sn); // -> " Fruit Titanesque, Inc." * }</pre> * * <p> Formattables are not necessarily safe for multithreaded access. Thread * safety is optional and may be enforced by classes that extend and implement * this interface. * * <p> Unless otherwise specified, passing a {@code null} argument to * any method in this interface will cause a {@link * NullPointerException} to be thrown. * * @since 1.5 */ public interface Formattable { /** * Formats the object using the provided {@link Formatter formatter}. * * @param formatter * The {@link Formatter formatter}. Implementing classes may call * {@link Formatter#out() formatter.out()} or {@link * Formatter#locale() formatter.locale()} to obtain the {@link * Appendable} or {@link Locale} used by this * {@code formatter} respectively. * * @param flags * The flags modify the output format. The value is interpreted as * a bitmask. Any combination of the following flags may be set: * {@link FormattableFlags#LEFT_JUSTIFY}, {@link * FormattableFlags#UPPERCASE}, and {@link * FormattableFlags#ALTERNATE}. If no flags are set, the default * formatting of the implementing class will apply. * * @param width * The minimum number of characters to be written to the output. * If the length of the converted value is less than the * {@code width} then the output will be padded by * <code>' '</code> until the total number of characters * equals width. The padding is at the beginning by default. If * the {@link FormattableFlags#LEFT_JUSTIFY} flag is set then the * padding will be at the end. If {@code width} is {@code -1} * then there is no minimum. * * @param precision * The maximum number of characters to be written to the output. * The precision is applied before the width, thus the output will * be truncated to {@code precision} characters even if the * {@code width} is greater than the {@code precision}. If * {@code precision} is {@code -1} then there is no explicit * limit on the number of characters. * * @throws IllegalFormatException * If any of the parameters are invalid. For specification of all * possible formatting errors, see the <a * href="../util/Formatter.html#detail">Details</a> section of the * formatter class specification. */ void formatTo(Formatter formatter, int flags, int width, int precision); }