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public interface Formattable
The Formattable interface must be implemented by any class that needs to perform custom formatting using the '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:
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); } }
When used in conjunction with the {@link java.util.Formatter}, the above class produces the following output for various format strings.
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."
Formattables are not necessarily safe for multithreaded access. Thread safety is optional and may be enforced by classes that extend and implement this interface.
Unless otherwise specified, passing a null argument to any method in this interface will cause a {@link NullPointerException} to be thrown.
Method Summary | |
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void |
Formats the object using the provided java.util.Formatter. |
Method Detail |
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public void formatTo(Formatter formatter, int flags, int width, int precision)
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
formatter respectively.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.width
- The minimum number of characters to be written to the output.
If the length of the converted value is less than the
width then the output will be padded by
' ' 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 width is -1
then there is no minimum.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 precision characters even if the
width is greater than the precision. If
precision is -1 then there is no explicit
limit on the number of characters.
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