Java implements how to retain the number of decimal places for double data

1. Return double type

1. Can be rounded

 double d = 114.145;
 d = (double) Math.round(d * 100) / 100;
System.out.println(d);

2. BigDecimal.ROUND_HALF_UP means rounding, and BigDecimal.ROUND_HALF_DOWN also means rounding. Enter, BigDecimal.ROUND_UP means carry processing (that is, directly add 1), BigDecimal.ROUND_DOWN means directly removing the mantissa.

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 double d = 114.145;
 BigDecimal b = new BigDecimal(d);
 d = b.setScale(2, BigDecimal.ROUND_HALF_UP).doubleValue();        
 System.out.println(d);

2. Returning the String type

1 and #.00 means retaining the last two digits. The processing method is to directly cut off the unnecessary mantissas without rounding.

 double d = 114.145;
 DecimalFormat df = new DecimalFormat("#.00");
 String str = df.format(d);
 System.out.println(str);

2. %.2f means retaining the last two digits and can be rounded

1 double d = 114.145;
2 String.format("%.2f", d);

3. RoundingMode.HALF_DOWN means rounding. The absolute value of a negative number is first taken, then rounded and then negative. RoundingMode.HALF_UP: Indicates rounding. Negative numbers first take the absolute value and then round to the nearest six and then make the negative number

 double d = 114.145
 NumberFormat nf = NumberFormat.getNumberInstance();
 // 保留两位小数
 nf.setMaximumFractionDigits(2); 
 // 如果不需要四舍五入，可以使用RoundingMode.DOWN
 nf.setRoundingMode(RoundingMode.UP);
 System.out.println(nf.format(d));

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