StringAlign.java

package chapter3;

import java.text.FieldPosition;
import java.text.Format;
import java.text.ParsePosition;

      

public class StringAlign extends Format {
private static final long serialVersionUID = 1L;
public enum Justify {
/* Constant for left justification. */
LEFT,
/* Constant for centering. */
CENTER,
/** Constant for right-justified Strings. */
RIGHT,
}
/** Current justification */
private Justify just;
/** Current max lengths */
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 maxChars - the maximum length of the output
* @param just - one of the enum values LEFT, CENTER or RIGHT
*/
public StringAlign(int maxChars, Justify just) {
switch(just) {
case LEFT:
case CENTER:
case 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 input, StringBuffer where, FieldPosition ignore) {
String s = input.toString();
String wanted = s.substring(0, Math.min(s.length(), maxChars));
// Get the spaces in the right place.
switch (just) {
case RIGHT:
pad(where, maxChars - wanted.length());
where.append(wanted);
break;
case CENTER:
int toAdd = maxChars - wanted.length();
pad(where, toAdd/2);
where.append(wanted);
pad(where, toAdd - toAdd/2);
break;
case 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;
}
}