DecimalFormat と四捨五入処理

import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.util.Locale;

 * @author King
public class DecimalFormatTest {

    public static void main(String[] args) {
        NumberFormat nemf = NumberFormat.getPercentInstance(Locale.JAPAN);
        DecimalFormat decf = (DecimalFormat)nemf;
        double d1 = 1.0015;
        System.out.println(d1+ “=>” + decf.format(d1));
        double d2 = 1.0025;
        System.out.println(d2+ “=>” + decf.format(d2));




クラス DecimalFormat

DecimalFormat はフォーマットに直近への丸め (ROUND_HALF_EVEN を参照) を使用します。


public static final int ROUND_HALF_EVEN

「もっとも近い数字」 に丸めるモードです。ただし、両隣りの数字が等距離の場合は偶数側に丸めます。破棄する小数部の左辺の桁が奇数の場合は ROUND_HALF_UP のように動作し、偶数の場合は ROUND_HALF_DOWN のように動作します。この丸めモードは、連続する計算で繰り返し適用される場合に累積エラーを最少にします。

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