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With inspiration from other libraries
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.math3.fraction;
import java.text.FieldPosition;
import java.text.NumberFormat;
import java.text.ParsePosition;
import org.apache.commons.math3.exception.util.LocalizedFormats;
import org.apache.commons.math3.exception.NullArgumentException;
import org.apache.commons.math3.util.FastMath;
import org.apache.commons.math3.util.MathUtils;
/**
* Formats a Fraction number in proper format. The number format for each of
* the whole number, numerator and, denominator can be configured.
*
* Minus signs are only allowed in the whole number part - i.e.,
* "-3 1/2" is legitimate and denotes -7/2, but "-3 -1/2" is invalid and
* will result in a ParseException.
*
* @since 1.1
*/
public class ProperFractionFormat extends FractionFormat {
/** Serializable version identifier */
private static final long serialVersionUID = 760934726031766749L;
/** The format used for the whole number. */
private NumberFormat wholeFormat;
/**
* Create a proper formatting instance with the default number format for
* the whole, numerator, and denominator.
*/
public ProperFractionFormat() {
this(getDefaultNumberFormat());
}
/**
* Create a proper formatting instance with a custom number format for the
* whole, numerator, and denominator.
* @param format the custom format for the whole, numerator, and
* denominator.
*/
public ProperFractionFormat(NumberFormat format) {
this(format, (NumberFormat)format.clone(), (NumberFormat)format.clone());
}
/**
* Create a proper formatting instance with a custom number format for each
* of the whole, numerator, and denominator.
* @param wholeFormat the custom format for the whole.
* @param numeratorFormat the custom format for the numerator.
* @param denominatorFormat the custom format for the denominator.
*/
public ProperFractionFormat(NumberFormat wholeFormat,
NumberFormat numeratorFormat,
NumberFormat denominatorFormat)
{
super(numeratorFormat, denominatorFormat);
setWholeFormat(wholeFormat);
}
/**
* Formats a {@link Fraction} object to produce a string. The fraction
* is output in proper format.
*
* @param fraction the object to format.
* @param toAppendTo where the text is to be appended
* @param pos On input: an alignment field, if desired. On output: the
* offsets of the alignment field
* @return the value passed in as toAppendTo.
*/
@Override
public StringBuffer format(Fraction fraction, StringBuffer toAppendTo,
FieldPosition pos) {
pos.setBeginIndex(0);
pos.setEndIndex(0);
int num = fraction.getNumerator();
int den = fraction.getDenominator();
int whole = num / den;
num %= den;
if (whole != 0) {
getWholeFormat().format(whole, toAppendTo, pos);
toAppendTo.append(' ');
num = FastMath.abs(num);
}
getNumeratorFormat().format(num, toAppendTo, pos);
toAppendTo.append(" / ");
getDenominatorFormat().format(den, toAppendTo, pos);
return toAppendTo;
}
/**
* Access the whole format.
* @return the whole format.
*/
public NumberFormat getWholeFormat() {
return wholeFormat;
}
/**
* Parses a string to produce a {@link Fraction} object. This method
* expects the string to be formatted as a proper fraction.
*
* Minus signs are only allowed in the whole number part - i.e.,
* "-3 1/2" is legitimate and denotes -7/2, but "-3 -1/2" is invalid and
* will result in a ParseException.
*
* @param source the string to parse
* @param pos input/ouput parsing parameter.
* @return the parsed {@link Fraction} object.
*/
@Override
public Fraction parse(String source, ParsePosition pos) {
// try to parse improper fraction
Fraction ret = super.parse(source, pos);
if (ret != null) {
return ret;
}
int initialIndex = pos.getIndex();
// parse whitespace
parseAndIgnoreWhitespace(source, pos);
// parse whole
Number whole = getWholeFormat().parse(source, pos);
if (whole == null) {
// invalid integer number
// set index back to initial, error index should already be set
// character examined.
pos.setIndex(initialIndex);
return null;
}
// parse whitespace
parseAndIgnoreWhitespace(source, pos);
// parse numerator
Number num = getNumeratorFormat().parse(source, pos);
if (num == null) {
// invalid integer number
// set index back to initial, error index should already be set
// character examined.
pos.setIndex(initialIndex);
return null;
}
if (num.intValue() < 0) {
// minus signs should be leading, invalid expression
pos.setIndex(initialIndex);
return null;
}
// parse '/'
int startIndex = pos.getIndex();
char c = parseNextCharacter(source, pos);
switch (c) {
case 0 :
// no '/'
// return num as a fraction
return new Fraction(num.intValue(), 1);
case '/' :
// found '/', continue parsing denominator
break;
default :
// invalid '/'
// set index back to initial, error index should be the last
// character examined.
pos.setIndex(initialIndex);
pos.setErrorIndex(startIndex);
return null;
}
// parse whitespace
parseAndIgnoreWhitespace(source, pos);
// parse denominator
Number den = getDenominatorFormat().parse(source, pos);
if (den == null) {
// invalid integer number
// set index back to initial, error index should already be set
// character examined.
pos.setIndex(initialIndex);
return null;
}
if (den.intValue() < 0) {
// minus signs must be leading, invalid
pos.setIndex(initialIndex);
return null;
}
int w = whole.intValue();
int n = num.intValue();
int d = den.intValue();
return new Fraction(((FastMath.abs(w) * d) + n) * MathUtils.copySign(1, w), d);
}
/**
* Modify the whole format.
* @param format The new whole format value.
* @throws NullArgumentException if {@code format} is {@code null}.
*/
public void setWholeFormat(NumberFormat format) {
if (format == null) {
throw new NullArgumentException(LocalizedFormats.WHOLE_FORMAT);
}
this.wholeFormat = format;
}
}