Formattable.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * accompanied this code).
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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>'&nbsp;&nbsp;'</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);
}