1、BigDecimal為不可變對象，每次“操作”都會返回新對象。

2、[精度]precision、[非標度值]unscale、[標度]scale

//正數的[精度]precision、[非標度值]unscale、[標度]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());//----------負數的[精度]precision、[非標度值]unscale、[標度]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、強制設置[標度]scale

//強制設置[標度]scale //----scale默認的0設置為3 BigDecimal de1 = new BigDecimal("125"); System.out.println( "默認scale為0：" + de1 ); System.out.println( "強制設置scale為3：" + de1.setScale(3) );//----scale由初始的2設置為5 de1 = new BigDecimal("28.02"); System.out.println( "初始scale為2：" + de1 ); System.out.println( "強制設置scale為5：" + de1.setScale(5) );//----scale由初始的7設置為2 de1 = new BigDecimal("177.1234567"); System.out.println( "初始scale為7：" + de1 ); try{//精度由大變小(7->2)必須設置舍入規則System.out.println( "強制設置scale為2：" + de1.setScale(2) ); }catch(Exception e){System.out.println( e.getMessage() ); } System.out.println( "強制設置scale為2：" + de1.setScale(2, RoundingMode.HALF_UP) );
4、舍入詳細示例

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，趨近最近的數，0.333∞ -> 0 System.out.println("ROUND_HALF_DOWN：1/3 = " + b1.divide(b3, RoundingMode.HALF_DOWN) ); //按指定精度，趨近最近的數，0.333∞ -> 0 System.out.println("ROUND_HALF_UP：1/3 = " + b1.divide(b3, RoundingMode.HALF_UP) );//按指定精度，趨近最近的數，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，趨近最近的數，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，趨近最近的數，0.333∞ -> 1 System.out.println("ROUND_HALF_DOWN：2/3 = " + b2.divide(b3, RoundingMode.HALF_DOWN) ); //按指定精度，趨近最近的數，0.333∞ -> 1 System.out.println("ROUND_HALF_UP：2/3 = " + b2.divide(b3, RoundingMode.HALF_UP) );//按指定精度，趨近最近的數，0.5 -> 偶數 //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) );//明確知道結果，否則拋異常 System.out.println("ROUND_UNNECESSARY：2 = " + b2.setScale(2, RoundingMode.UNNECESSARY)); try{//計算中的結果無法使用：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

//計算數的位數較小，最后結果都一樣 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最大為7 //DECIMAL64-->precision最大為16 //DECIMAL128-->precision最大為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 對象用作 SortedMap 中的鍵或 SortedSet 中的元素，則應特別小心，因為 BigDecimal 的自然排序與 equals 方法不一致。

Map接口是按照 equals 操作定義的，但有序映射SortedMap使用它的 compareTo（或 compare）方法對所有鍵進行比較

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 對象用作 SortedMap 中的鍵或 SortedSet 中的元素，則應特別小心，因為 BigDecimal 的自然排序與 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 操作定義的，但有序映射SortedMap使用它的 compareTo（或 compare）方法對所有鍵進行比較
7、綜合示例

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(){//正數的[精度]precision、[非標度值]unscale、[標度]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());//----------負數的[精度]precision、[非標度值]unscale、[標度]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());//強制設置[標度]scale//----scale默認的0設置為3BigDecimal de1 = new BigDecimal("125");System.out.println( "默認scale為0：" + de1 );System.out.println( "強制設置scale為3：" + de1.setScale(3) );//----scale由初始的2設置為5de1 = new BigDecimal("28.02");System.out.println( "初始scale為2：" + de1 );System.out.println( "強制設置scale為5：" + de1.setScale(5) );//----scale由初始的7設置為2de1 = new BigDecimal("177.1234567");System.out.println( "初始scale為7：" + de1 );try{//精度由大變小(7->2)必須設置舍入規則System.out.println( "強制設置scale為2：" + de1.setScale(2) );}catch(Exception e){System.out.println( e.getMessage() );}System.out.println( "強制設置scale為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，趨近最近的數，0.333∞ -> 0System.out.println("ROUND_HALF_DOWN：1/3 = " + b1.divide(b3, RoundingMode.HALF_DOWN) );//按指定精度，趨近最近的數，0.333∞ -> 0System.out.println("ROUND_HALF_UP：1/3 = " + b1.divide(b3, RoundingMode.HALF_UP) );//按指定精度，趨近最近的數，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，趨近最近的數，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，趨近最近的數，0.333∞ -> 1System.out.println("ROUND_HALF_DOWN：2/3 = " + b2.divide(b3, RoundingMode.HALF_DOWN) );//按指定精度，趨近最近的數，0.333∞ -> 1System.out.println("ROUND_HALF_UP：2/3 = " + b2.divide(b3, RoundingMode.HALF_UP) );//按指定精度，趨近最近的數，0.5 -> 偶數//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) );//明確知道結果，否則拋異常System.out.println("ROUND_UNNECESSARY：2 = " + b2.setScale(2, RoundingMode.UNNECESSARY));try{//計算中的結果無法使用：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(){//計算數的位數較小，最后結果都一樣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最大為7//DECIMAL64-->precision最大為16//DECIMAL128-->precision最大為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 對象用作 SortedMap 中的鍵或 SortedSet 中的元素，則應特別小心，因為 BigDecimal 的自然排序與 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 操作定義的，但有序映射SortedMap使用它的 compareTo（或 compare）方法對所有鍵進行比較}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的內部信息* @param decimal*/static void info( final BigDecimal decimal ){System.out.println( decimal + " precision=" + decimal.precision() +",unscale=" + decimal.unscaledValue()+ ",scale=" + decimal.scale());}}

創作挑戰賽新人創作獎勵來咯，堅持創作打卡瓜分現金大獎

總結

以上是生活随笔為你收集整理的BigDecimal总结的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。