BigDecimal总结

1、BigDecimal为不可变对象，每次“操作”都会返回新对象。

2、[精度]precision、[非标度值]unscale、[标度]scale

//正数的[精度]precision、[非标度值]unscale、[标度]scale
//0 precision=1,unscale=0,scale=0
BigDecimal tmp = new BigDecimal("0");
System.out.println( "0 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale() );tmp = new BigDecimal("0.0");
//0.0 precision=1,unscale=0,scale=1
System.out.println( "0.0 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());tmp = new BigDecimal("1");
//1 precision=1,unscale=1,scale=0
System.out.println( "1 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());tmp = new BigDecimal("1.0");
//1.0 precision=2,unscale=10,scale=1
System.out.println( "1.0 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());tmp = new BigDecimal("0.1");
//0.1 precision=1,unscale=1,scale=1
System.out.println( "0.1 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());tmp = new BigDecimal("122.000");
//122.000 precision=6,unscale=122000,scale=3
System.out.println( "122.000 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());//----------负数的[精度]precision、[非标度值]unscale、[标度]scale
//-0 precision=1,unscale=0,scale=0
tmp = new BigDecimal("-0");
System.out.println( "-0 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale() );tmp = new BigDecimal("-0.0");
//-0.0 precision=1,unscale=0,scale=1
System.out.println( "-0.0 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());tmp = new BigDecimal("-1");
//-1 precision=1,unscale=-1,scale=0
System.out.println( "-1 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());tmp = new BigDecimal("-1.0");
//-1.0 precision=2,unscale=-10,scale=1
System.out.println( "-1.0 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());tmp = new BigDecimal("-0.1");
//-0.1 precision=1,unscale=-1,scale=1
System.out.println( "-0.1 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());tmp = new BigDecimal("-122.000");
//-122.000 precision=6,unscale=-122000,scale=3
System.out.println( "-122.000 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());

3、强制设置[标度]scale

//强制设置[标度]scale
//----scale默认的0设置为3
BigDecimal de1 = new BigDecimal("125");
System.out.println( "默认scale为0：" + de1 );
System.out.println( "强制设置scale为3：" + de1.setScale(3) );//----scale由初始的2设置为5
de1 = new BigDecimal("28.02");
System.out.println( "初始scale为2：" + de1 );
System.out.println( "强制设置scale为5：" + de1.setScale(5) );//----scale由初始的7设置为2
de1 = new BigDecimal("177.1234567");
System.out.println( "初始scale为7：" + de1 );
try{//精度由大变小(7->2)必须设置舍入规则System.out.println( "强制设置scale为2：" + de1.setScale(2) );
}catch(Exception e){System.out.println( e.getMessage() );
}
System.out.println( "强制设置scale为2：" + de1.setScale(2, RoundingMode.HALF_UP) );

4、舍入详细示例

BigDecimal b1 = new BigDecimal("1");
BigDecimal b2 = new BigDecimal("2");
BigDecimal b3 = new BigDecimal("3");
//按指定精度，向上0.333∞ -> 1
System.out.println("ROUND_CEILING：1/3 = " + b1.divide(b3, RoundingMode.CEILING) );
//按指定精度，向上0.333∞ -> 1
System.out.println("ROUND_UP：1/3 = " + b1.divide(b3, RoundingMode.UP) );//按指定精度，向下0.333∞ -> 0
System.out.println("ROUND_DOWN：1/3 = " + b1.divide(b3, RoundingMode.DOWN) );
//按指定精度，向下0.333∞ -> 0
System.out.println("ROUND_FLOOR：1/3 = " + b1.divide(b3, RoundingMode.FLOOR) );//按指定精度，趋近最近的数，0.333∞ -> 0
System.out.println("ROUND_HALF_DOWN：1/3 = " + b1.divide(b3, RoundingMode.HALF_DOWN) );
//按指定精度，趋近最近的数，0.333∞ -> 0
System.out.println("ROUND_HALF_UP：1/3 = " + b1.divide(b3, RoundingMode.HALF_UP) );//按指定精度，趋近最近的数，0.5向下 0.5-> 0
System.out.println("ROUND_HALF_DOWN：1/2 = " + b1.divide(b2, RoundingMode.HALF_DOWN) );
//按指定精度，趋近最近的数，0.5向上 0.5-> 1
System.out.println("ROUND_HALF_UP：1/2 = " + b1.divide(b2, RoundingMode.HALF_UP) );//按指定精度，趋近最近的数，0.333∞ -> 1
System.out.println("ROUND_HALF_DOWN：2/3 = " + b2.divide(b3, RoundingMode.HALF_DOWN) );
//按指定精度，趋近最近的数，0.333∞ -> 1
System.out.println("ROUND_HALF_UP：2/3 = " + b2.divide(b3, RoundingMode.HALF_UP) );//按指定精度，趋近最近的数，0.5 -> 偶数
//ROUND_HALF_EVEN：1/3 = 0
System.out.println("ROUND_HALF_EVEN：1/3 = " + b1.divide(b3, RoundingMode.HALF_EVEN) );
//ROUND_HALF_EVEN：1/2 = 0
System.out.println("ROUND_HALF_EVEN：1/2 = " + b1.divide(b2, RoundingMode.HALF_EVEN) );
//ROUND_HALF_EVEN：2/3 = 1
System.out.println("ROUND_HALF_EVEN：2/3 = " + b2.divide(b3, RoundingMode.HALF_EVEN) );//明确知道结果，否则抛异常
System.out.println("ROUND_UNNECESSARY：2 = " + b2.setScale(2, RoundingMode.UNNECESSARY));
try{//计算中的结果无法使用：ROUND_UNNECESSARYSystem.out.println("ROUND_UNNECESSARY：1/2 = " + b1.divide(b2, RoundingMode.UNNECESSARY) );
}catch( Exception e ){//Rounding necessarySystem.out.println( e.getMessage() );
}

5、MathContext示例

//计算数的位数较小，最后结果都一样
BigDecimal b1 = new BigDecimal( "23.323" );
BigDecimal b2 = new BigDecimal( "323.57" );
//346.893 precision=6,unscale=346893,scale=3
info( b1.add(b2, MathContext.DECIMAL32) );
//346.893 precision=6,unscale=346893,scale=3
info( b1.add(b2, MathContext.DECIMAL64) );
//346.893 precision=6,unscale=346893,scale=3
info( b1.add(b2, MathContext.DECIMAL128) );//DECIMAL32-->precision最大为7
//DECIMAL64-->precision最大为16
//DECIMAL128-->precision最大为34
b1 = new BigDecimal( "1231243434341223.25532323" );
b2 = new BigDecimal( "4532323.55457" );
//1.231243E+15 precision=7,unscale=1231243,scale=-9
info( b1.add(b2, MathContext.DECIMAL32) );
//1231243438873547 precision=16,unscale=1231243438873547,scale=0
info( b1.add(b2, MathContext.DECIMAL64) );
//1231243438873546.80989323 precision=24,unscale=123124343887354680989323,scale=8
info( b1.add(b2, MathContext.DECIMAL128) );

6、equals和sort

注：如果 BigDecimal 对象用作 SortedMap 中的键或 SortedSet 中的元素，则应特别小心，因为 BigDecimal 的自然排序与 equals 方法不一致。

Map接口是按照 equals 操作定义的，但有序映射SortedMap使用它的 compareTo（或 compare）方法对所有键进行比较

BigDecimal b1 = new BigDecimal("28.000");
BigDecimal b2 = new BigDecimal(28);
//28.000 precision=5,unscale=28000,scale=3
info( b1 );
//28 precision=2,unscale=28,scale=0
info( b2 );
//false
System.out.println( b1.equals(b2) );
System.out.println( "b1.hashCode=" + b1.hashCode() );
System.out.println( "b2.hashCode=" + b2.hashCode() );
//0
System.out.println( b1.compareTo(b2) );//注：如果 BigDecimal 对象用作 SortedMap 中的键或 SortedSet 中的元素，则应特别小心，因为 BigDecimal 的自然排序与 equals 方法不一致。
Map<BigDecimal, String> treeMap = new TreeMap<BigDecimal,String>();
treeMap.put(b1, "28.000");
treeMap.put(b2, "28");
treeMap.put(new BigDecimal("12"), "12");
//{12=12, 28.000=28}
System.out.println( treeMap );Map<BigDecimal, String> hashMap = new HashMap<BigDecimal, String>();
hashMap.put(b1, "28.000");
hashMap.put(b2, "28");
hashMap.put(new BigDecimal("12"), "12");
//{28.000=28.000, 12=12, 28=28}
System.out.println( hashMap );// Map接口是按照 equals 操作定义的，但有序映射SortedMap使用它的 compareTo（或 compare）方法对所有键进行比较

7、综合示例

static void actionByDouble(){String[] arr = new String[]{"3649926.00","213582.00","253270.00","172841.00","204571.00","177974.00","189629.00","155114.00","135878.00","119562.00","132559.00","159562.00","161837.00","103169.00","136250.00","132953.00","121470.00000000001"};BigDecimal total = BigDecimal.ZERO;for( String s : arr ){double d = Double.valueOf(s);BigDecimal num = new BigDecimal(d);total = total.add( num );}//actionByDouble: total=6220147.00System.out.println( "actionByDouble: total=" + total.setScale(2, BigDecimal.ROUND_HALF_UP) );
}

public class BigDecimalTest {/*** @param args*/public static void main(final String[] args) {actionByString();actionByDouble();test();matchContext();equalsAndSort();}static void test(){//正数的[精度]precision、[非标度值]unscale、[标度]scale//0 precision=1,unscale=0,scale=0BigDecimal tmp = new BigDecimal("0");System.out.println( "0 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale() );tmp = new BigDecimal("0.0");//0.0 precision=1,unscale=0,scale=1System.out.println( "0.0 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());tmp = new BigDecimal("1");//1 precision=1,unscale=1,scale=0System.out.println( "1 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());tmp = new BigDecimal("1.0");//1.0 precision=2,unscale=10,scale=1System.out.println( "1.0 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());tmp = new BigDecimal("0.1");//0.1 precision=1,unscale=1,scale=1System.out.println( "0.1 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());tmp = new BigDecimal("122.000");//122.000 precision=6,unscale=122000,scale=3System.out.println( "122.000 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());//----------负数的[精度]precision、[非标度值]unscale、[标度]scale//-0 precision=1,unscale=0,scale=0tmp = new BigDecimal("-0");System.out.println( "-0 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale() );tmp = new BigDecimal("-0.0");//-0.0 precision=1,unscale=0,scale=1System.out.println( "-0.0 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());tmp = new BigDecimal("-1");//-1 precision=1,unscale=-1,scale=0System.out.println( "-1 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());tmp = new BigDecimal("-1.0");//-1.0 precision=2,unscale=-10,scale=1System.out.println( "-1.0 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());tmp = new BigDecimal("-0.1");//-0.1 precision=1,unscale=-1,scale=1System.out.println( "-0.1 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());tmp = new BigDecimal("-122.000");//-122.000 precision=6,unscale=-122000,scale=3System.out.println( "-122.000 precision=" + tmp.precision() +",unscale=" + tmp.unscaledValue()+ ",scale=" + tmp.scale());//强制设置[标度]scale//----scale默认的0设置为3BigDecimal de1 = new BigDecimal("125");System.out.println( "默认scale为0：" + de1 );System.out.println( "强制设置scale为3：" + de1.setScale(3) );//----scale由初始的2设置为5de1 = new BigDecimal("28.02");System.out.println( "初始scale为2：" + de1 );System.out.println( "强制设置scale为5：" + de1.setScale(5) );//----scale由初始的7设置为2de1 = new BigDecimal("177.1234567");System.out.println( "初始scale为7：" + de1 );try{//精度由大变小(7->2)必须设置舍入规则System.out.println( "强制设置scale为2：" + de1.setScale(2) );}catch(Exception e){System.out.println( e.getMessage() );}System.out.println( "强制设置scale为2：" + de1.setScale(2, RoundingMode.HALF_UP) );BigDecimal b1 = new BigDecimal("1");BigDecimal b2 = new BigDecimal("2");BigDecimal b3 = new BigDecimal("3");//按指定精度，向上0.333∞ -> 1System.out.println("ROUND_CEILING：1/3 = " + b1.divide(b3, RoundingMode.CEILING) );//按指定精度，向上0.333∞ -> 1System.out.println("ROUND_UP：1/3 = " + b1.divide(b3, RoundingMode.UP) );//按指定精度，向下0.333∞ -> 0System.out.println("ROUND_DOWN：1/3 = " + b1.divide(b3, RoundingMode.DOWN) );//按指定精度，向下0.333∞ -> 0System.out.println("ROUND_FLOOR：1/3 = " + b1.divide(b3, RoundingMode.FLOOR) );//按指定精度，趋近最近的数，0.333∞ -> 0System.out.println("ROUND_HALF_DOWN：1/3 = " + b1.divide(b3, RoundingMode.HALF_DOWN) );//按指定精度，趋近最近的数，0.333∞ -> 0System.out.println("ROUND_HALF_UP：1/3 = " + b1.divide(b3, RoundingMode.HALF_UP) );//按指定精度，趋近最近的数，0.5向下 0.5-> 0System.out.println("ROUND_HALF_DOWN：1/2 = " + b1.divide(b2, RoundingMode.HALF_DOWN) );//按指定精度，趋近最近的数，0.5向上 0.5-> 1System.out.println("ROUND_HALF_UP：1/2 = " + b1.divide(b2, RoundingMode.HALF_UP) );//按指定精度，趋近最近的数，0.333∞ -> 1System.out.println("ROUND_HALF_DOWN：2/3 = " + b2.divide(b3, RoundingMode.HALF_DOWN) );//按指定精度，趋近最近的数，0.333∞ -> 1System.out.println("ROUND_HALF_UP：2/3 = " + b2.divide(b3, RoundingMode.HALF_UP) );//按指定精度，趋近最近的数，0.5 -> 偶数//ROUND_HALF_EVEN：1/3 = 0System.out.println("ROUND_HALF_EVEN：1/3 = " + b1.divide(b3, RoundingMode.HALF_EVEN) );//ROUND_HALF_EVEN：1/2 = 0System.out.println("ROUND_HALF_EVEN：1/2 = " + b1.divide(b2, RoundingMode.HALF_EVEN) );//ROUND_HALF_EVEN：2/3 = 1System.out.println("ROUND_HALF_EVEN：2/3 = " + b2.divide(b3, RoundingMode.HALF_EVEN) );//明确知道结果，否则抛异常System.out.println("ROUND_UNNECESSARY：2 = " + b2.setScale(2, RoundingMode.UNNECESSARY));try{//计算中的结果无法使用：ROUND_UNNECESSARYSystem.out.println("ROUND_UNNECESSARY：1/2 = " + b1.divide(b2, RoundingMode.UNNECESSARY) );}catch( Exception e ){//Rounding necessarySystem.out.println( e.getMessage() );}}static void matchContext(){//计算数的位数较小，最后结果都一样BigDecimal b1 = new BigDecimal( "23.323" );BigDecimal b2 = new BigDecimal( "323.57" );//346.893 precision=6,unscale=346893,scale=3info( b1.add(b2, MathContext.DECIMAL32) );//346.893 precision=6,unscale=346893,scale=3info( b1.add(b2, MathContext.DECIMAL64) );//346.893 precision=6,unscale=346893,scale=3info( b1.add(b2, MathContext.DECIMAL128) );//DECIMAL32-->precision最大为7//DECIMAL64-->precision最大为16//DECIMAL128-->precision最大为34b1 = new BigDecimal( "1231243434341223.25532323" );b2 = new BigDecimal( "4532323.55457" );//1.231243E+15 precision=7,unscale=1231243,scale=-9info( b1.add(b2, MathContext.DECIMAL32) );//1231243438873547 precision=16,unscale=1231243438873547,scale=0info( b1.add(b2, MathContext.DECIMAL64) );//1231243438873546.80989323 precision=24,unscale=123124343887354680989323,scale=8info( b1.add(b2, MathContext.DECIMAL128) );}static void equalsAndSort(){BigDecimal b1 = new BigDecimal("28.000");BigDecimal b2 = new BigDecimal(28);//28.000 precision=5,unscale=28000,scale=3info( b1 );//28 precision=2,unscale=28,scale=0info( b2 );//falseSystem.out.println( b1.equals(b2) );System.out.println( "b1.hashCode=" + b1.hashCode() );System.out.println( "b2.hashCode=" + b2.hashCode() );//0System.out.println( b1.compareTo(b2) );//注：如果 BigDecimal 对象用作 SortedMap 中的键或 SortedSet 中的元素，则应特别小心，因为 BigDecimal 的自然排序与 equals 方法不一致。Map<BigDecimal, String> treeMap = new TreeMap<BigDecimal,String>();treeMap.put(b1, "28.000");treeMap.put(b2, "28");treeMap.put(new BigDecimal("12"), "12");//{12=12, 28.000=28}System.out.println( treeMap );Map<BigDecimal, String> hashMap = new HashMap<BigDecimal, String>();hashMap.put(b1, "28.000");hashMap.put(b2, "28");hashMap.put(new BigDecimal("12"), "12");//{28.000=28.000, 12=12, 28=28}System.out.println( hashMap );// Map接口是按照 equals 操作定义的，但有序映射SortedMap使用它的 compareTo（或 compare）方法对所有键进行比较}static void actionByString(){String[] arr = new String[]{"3649926.00","213582.00","253270.00","172841","204571","177974","189629","155114","135878","119562","132559","159562","161837","103169","136250","132953","121470.00000434"};BigDecimal total = BigDecimal.ZERO;for( String s : arr ){BigDecimal num = new BigDecimal(s);total = total.add( num );}//actionByString: total=6220147.00System.out.println( "actionByString: total=" + total.setScale(2, RoundingMode.HALF_UP) );}static void actionByDouble(){String[] arr = new String[]{"3649926.00","213582.00","253270.00","172841.00","204571.00","177974.00","189629.00","155114.00","135878.00","119562.00","132559.00","159562.00","161837.00","103169.00","136250.00","132953.00","121470.00000000001"};BigDecimal total = BigDecimal.ZERO;for( String s : arr ){double d = Double.valueOf(s);BigDecimal num = new BigDecimal(d);total = total.add( num );}//actionByDouble: total=6220147.00System.out.println( "actionByDouble: total=" + total.setScale(2, BigDecimal.ROUND_HALF_UP) );}/*** 指定BigDecimal的内部信息* @param decimal*/static void info( final BigDecimal decimal ){System.out.println( decimal + " precision=" + decimal.precision() +",unscale=" + decimal.unscaledValue()+ ",scale=" + decimal.scale());}}

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