/** Bare-minimum String formatter (string aligner). */
public class StringAlign extends Format {
/* Constant for left justification. */
public static final int JUST_LEFT = 'l';
/* Constant for centering. */
public static final int JUST_CENTRE = 'c';
/* Centering Constant, for those who spell "centre" the American way. */
public static final int JUST_CENTER = JUST_CENTRE;
/** Constant for right-justified Strings. */
public static final int JUST_RIGHT = 'r';
/** Current justification */
private int just;
/** Current max length */
private int maxChars;
/** Construct a StringAlign formatter; length and alignment are
* passed to the Constructor instead of each format( ) call as the
* expected common use is in repetitive formatting e.g., page numbers.
* @param nChars - the length of the output
* @param just - one of JUST_LEFT, JUST_CENTRE or JUST_RIGHT
*/
public StringAlign(int maxChars, int just) {
switch(just) {
case JUST_LEFT:
case JUST_CENTRE:
case JUST_RIGHT:
this.just = just;
break;
default:
throw new IllegalArgumentException("invalid justification arg.");
}
if (maxChars < 0) {
throw new IllegalArgumentException("maxChars must be positive.");
}
this.maxChars = maxChars;
}
/** Format a String.
* @param input _ the string to be aligned
* @parm where - the StringBuffer to append it to.
* @param ignore - a FieldPosition (may be null, not used but
* specified by the general contract of Format).
*/
public StringBuffer format(
Object obj, StringBuffer where, FieldPosition ignore) {
String s = (String)obj;
String wanted = s.substring(0, Math.min(s.length( ), maxChars));
// Get the spaces in the right place.
switch (just) {
case JUST_RIGHT:
pad(where, maxChars - wanted.length( ));
where.append(wanted);
break;
case JUST_CENTRE:
int startPos = where.length( );
pad(where, (maxChars - wanted.length( ))/2);
where.append(wanted);
pad(where, (maxChars - wanted.length( ))/2);
// Adjust for "rounding error"
pad(where, maxChars - (where.length( ) - startPos));
break;
case JUST_LEFT:
where.append(wanted);
pad(where, maxChars - wanted.length( ));
break;
}
return where;
}
protected final void pad(StringBuffer to, int howMany) {
for (int i=0; i<howMany; i++)
to.append(' ');
}
/** Convenience Routine */
String format(String s) {
return format(s, new StringBuffer( ), null).toString( );
}
/** ParseObject is required, but not useful here. */
public Object parseObject (String source, ParsePosition pos) {
return source;
}
Is the code for the StringAlign class. Note that this class extends a class called Format. In the package java.text, there is a series of Format classes that all have at least one method called format( ). It is thus in a family with numerous other for- matters, such as DateFormat, NumberFormat, and others, that we’ll meet in upcoming chapters.
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