BigDecimal的8种round舍入模式
2024-04-11 01:07:26
写段代码，用一个数字（正数或负数），依次使用8种不同的模式，看i参数
public static void demo(BigDecimal bigDecimal, int scale){System.out.println();System.out.print(bigDecimal.toString()+"\t");//循环使用8种舍入模式for (int i =0 ;i<8;i++){try{System.out.print(bigDecimal.setScale(scale,i)+"\t");}catch (Exception e){System.out.printf(e.getMessage());}}}然后尽可能造多个不同的数字，默认保留0位小数，即scale为0，依次调用上面的demo方法：
BigDecimal aa = new BigDecimal("3.300");BigDecimal bb = new BigDecimal("3.344");BigDecimal cc = new BigDecimal("3.355");BigDecimal dd = new BigDecimal("3.356");BigDecimal ee = new BigDecimal("3.366");BigDecimal ff = new BigDecimal("3.512");BigDecimal gg = new BigDecimal("3.561");BigDecimal hh = new BigDecimal("3.169");BigDecimal ii = new BigDecimal("3.000");BigDecimal jj = new BigDecimal("3.001");BigDecimal ll = new BigDecimal("3.500");BigDecimal mm = new BigDecimal("4.500");BigDecimal aa1 = new BigDecimal("-3.300");BigDecimal bb1 = new BigDecimal("-3.344");BigDecimal cc1 = new BigDecimal("-3.355");BigDecimal dd1 = new BigDecimal("-3.356");BigDecimal ee1 = new BigDecimal("-3.366");BigDecimal ff1 = new BigDecimal("-3.512");BigDecimal gg1 = new BigDecimal("-3.561");BigDecimal hh1 = new BigDecimal("-3.169");BigDecimal ii1 = new BigDecimal("-3.000");BigDecimal jj1 = new BigDecimal("-3.001");BigDecimal ll1 = new BigDecimal("-3.500");BigDecimal mm1 = new BigDecimal("-4.500");demo(aa,0);demo(bb,0);demo(cc,0);demo(dd,0);demo(ee,0);demo(ff,0);demo(gg,0);demo(hh,0);demo(ii,0);demo(jj,0);demo(ll,0);demo(mm,0);System.out.println();System.out.println("------------------------------------------------------");demo(aa1,0);demo(bb1,0);demo(cc1,0);demo(dd1,0);demo(ee1,0);demo(ff1,0);demo(gg1,0);demo(hh1,0);demo(ii1,0);demo(jj1,0);demo(ll1,0);demo(mm1,0);控制台输出（格式化后的）：
1、正数：
值 ROUND_UP ROUND_DOWN ROUND_CEILING ROUND_FLOOR ROUND_HALF_UP ROUND_HALF_DOWN ROUND_HALF_EVEN ROUND_UNNECESSARY3.300 4 3 4 3 3 3 3 Rounding necessary---------------------------------------------------------------------------------------------------------------------------------------------------------------------3.344 4 3 4 3 3 3 3 Rounding necessary---------------------------------------------------------------------------------------------------------------------------------------------------------------------3.355 4 3 4 3 3 3 3 Rounding necessary---------------------------------------------------------------------------------------------------------------------------------------------------------------------3.356 4 3 4 3 3 3 3 Rounding necessary---------------------------------------------------------------------------------------------------------------------------------------------------------------------3.366 4 3 4 3 3 3 3 Rounding necessary---------------------------------------------------------------------------------------------------------------------------------------------------------------------3.512 4 3 4 3 4 4 4 Rounding necessary---------------------------------------------------------------------------------------------------------------------------------------------------------------------3.561 4 3 4 3 4 4 4 Rounding necessary---------------------------------------------------------------------------------------------------------------------------------------------------------------------3.169 4 3 4 3 3 3 3 Rounding necessary---------------------------------------------------------------------------------------------------------------------------------------------------------------------3.000 3 3 3 3 3 3 3 3 ---------------------------------------------------------------------------------------------------------------------------------------------------------------------3.001 4 3 4 3 3 3 3 Rounding necessary---------------------------------------------------------------------------------------------------------------------------------------------------------------------3.500 4 3 4 3 4 3 4 Rounding necessary---------------------------------------------------------------------------------------------------------------------------------------------------------------------4.500 5 4 5 4 5 4 4 Rounding necessary2、负数
值 ROUND_UP ROUND_DOWN ROUND_CEILING ROUND_FLOOR ROUND_HALF_UP ROUND_HALF_DOWN ROUND_HALF_EVEN ROUND_UNNECESSARY
-3.300 -4 -3 -3 -4 -3 -3 -3 Rounding necessary
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
-3.344 -4 -3 -3 -4 -3 -3 -3 Rounding necessary
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
-3.355 -4 -3 -3 -4 -3 -3 -3 Rounding necessary
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
-3.356 -4 -3 -3 -4 -3 -3 -3 Rounding necessary
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
-3.366 -4 -3 -3 -4 -3 -3 -3 Rounding necessary
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
-3.512 -4 -3 -3 -4 -4 -4 -4 Rounding necessary
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
-3.561 -4 -3 -3 -4 -4 -4 -4 Rounding necessary
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
-3.169 -4 -3 -3 -4 -3 -3 -3 Rounding necessary
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
-3.000 -3 -3 -3 -3 -3 -3 -3 -3
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
-3.001 -4 -3 -3 -4 -3 -3 -3 Rounding necessary
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
-3.500 -4 -3 -3 -4 -4 -3 -4 Rounding necessary
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
-4.500 -5 -4 -4 -5 -5 -4 -4 Rounding necessary每种模式分别介绍下：
零、无论是正数还是负数都是往0以外的方向
/*** Rounding mode to round away from zero. Always increments the* digit prior to a nonzero discarded fraction. Note that this rounding* mode never decreases the magnitude of the calculated value.*/public final static int ROUND_UP = 0;一、无论是正数还是负数都是往0的方向
/*** Rounding mode to round towards zero. Never increments the digit* prior to a discarded fraction (i.e., truncates). Note that this* rounding mode never increases the magnitude of the calculated value.*/public final static int ROUND_DOWN = 1;二、区分正负数，正数变大，负数也是变大
/*** Rounding mode to round towards positive infinity. If the* {@code BigDecimal} is positive, behaves as for* {@code ROUND_UP}; if negative, behaves as for* {@code ROUND_DOWN}. Note that this rounding mode never* decreases the calculated value.*/public final static int ROUND_CEILING = 2;三、区分正负数，正数变小，负数也是变小
/*** Rounding mode to round towards negative infinity. If the* {@code BigDecimal} is positive, behave as for* {@code ROUND_DOWN}; if negative, behave as for* {@code ROUND_UP}. Note that this rounding mode never* increases the calculated value.*/public final static int ROUND_FLOOR = 3;四、正数小数位大于等于0.5则变大，负数小数位大于等于0.5则变小，注意这里是包含0.5
/*** Rounding mode to round towards {@literal "nearest neighbor"}* unless both neighbors are equidistant, in which case round up.* Behaves as for {@code ROUND_UP} if the discarded fraction is* ≥ 0.5; otherwise, behaves as for {@code ROUND_DOWN}. Note* that this is the rounding mode that most of us were taught in* grade school.*/public final static int ROUND_HALF_UP = 4;五、正数小数位大于0.5则变大，负数小数位大于0.5则变小，注意这里是不包含0.5
/*** Rounding mode to round towards {@literal "nearest neighbor"}* unless both neighbors are equidistant, in which case round* down. Behaves as for {@code ROUND_UP} if the discarded* fraction is {@literal >} 0.5; otherwise, behaves as for* {@code ROUND_DOWN}.*/public final static int ROUND_HALF_DOWN = 5;六、此舍入模式也称为“银行家舍入法”，主要在美国使用。四舍六入，五分两种情况。如果前一位为奇数，则入位，否则舍去。
3.5->4但是4.5>4，因为3是奇数，4是偶数
/*** Rounding mode to round towards the {@literal "nearest neighbor"}* unless both neighbors are equidistant, in which case, round* towards the even neighbor. Behaves as for* {@code ROUND_HALF_UP} if the digit to the left of the* discarded fraction is odd; behaves as for* {@code ROUND_HALF_DOWN} if it's even. Note that this is the* rounding mode that minimizes cumulative error when applied* repeatedly over a sequence of calculations.*/public final static int ROUND_HALF_EVEN = 6;七、断言是有精度的，如果没有会报异常
/*** Rounding mode to assert that the requested operation has an exact* result, hence no rounding is necessary. If this rounding mode is* specified on an operation that yields an inexact result, an* {@code ArithmeticException} is thrown.*/public final static int ROUND_UNNECESSARY = 7;BigDecimal的8种round舍入模式相关推荐
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