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'rapiddweller Common' is an open source Java library forked from Databene Commons by Volker Bergmann. It provides extensions to the Java core library by utility classes, abstract concepts and concrete implementations.

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/*
 * Copyright (C) 2004-2015 Volker Bergmann ([email protected]).
 * All rights reserved.
 *
 * Licensed 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 com.rapiddweller.common;

import java.text.DecimalFormat;
import java.text.FieldPosition;
import java.text.Format;
import java.text.NumberFormat;
import java.text.ParsePosition;
import java.util.Locale;

/**
 * Rounds large numbers to the four most significant digits.
 * Created: 01.09.2007 16:19:14
 */
public class RoundedNumberFormat extends Format {

  private static final long serialVersionUID = 6188839664275513505L;

  @Override
  public StringBuffer format(Object obj, StringBuffer toAppendTo, FieldPosition pos) {
    return toAppendTo.append(format((Number) obj, 2));
  }

  @Override
  public Object parseObject(String source, ParsePosition pos) {
    throw new UnsupportedOperationException("Not supported");
  }

  /**
   * Format string.
   *
   * @param number         the number
   * @param fractionDigits the fraction digits
   * @return the string
   */
  public static String format(Number number, int fractionDigits) {
    NumberFormat nf = DecimalFormat.getInstance(Locale.US);
    //nf.setMinimumFractionDigits(fractionDigits);
    nf.setMaximumFractionDigits(fractionDigits);
    StringBuffer buffer = nf.format(number, new StringBuffer(), new FieldPosition(0));
    int nonNullDigits = 0;
    for (int i = 0; i < buffer.length(); i++) {
      char c = buffer.charAt(i);
      if (Character.isDigit(c)) {
        if (nonNullDigits >= 2) {
          buffer.setCharAt(i, '0');
        }
        nonNullDigits++;
      }
    }
    return buffer.toString();
  }

}