BAEL-2154 - BigDecimal and BigInteger article.

java-numbers/src/main/java/com/baeldung/maths/BigDecimalDemo.java

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+import java.math.BigDecimal;
+import java.math.RoundingMode;
+
+public class BigDecimalDemo {
+
+    /** Calculate total amount to be paid for an item rounded to cents..
+     * @param quantity
+     * @param unitPrice
+     * @param discountRate
+     * @param taxRate
+     * @return
+     */
+    public static BigDecimal calculateTotalAmount(BigDecimal quantity,
+        BigDecimal unitPrice, BigDecimal discountRate, BigDecimal taxRate) { 
+        BigDecimal amount = quantity.multiply(unitPrice);
+        BigDecimal discount = amount.multiply(discountRate);
+        BigDecimal discountedAmount = amount.subtract(discount);
+        BigDecimal tax = taxRate.multiply(taxRate);
+        BigDecimal total = discountedAmount.add(tax);
+
+        // round to 2 decimal places using HALF_EVEN
+        BigDecimal roundedTotal = total.setScale(2, RoundingMode.HALF_EVEN);
+        
+        return roundedTotal;
+    }
+
+}

java-numbers/src/test/java/com/baeldung/maths/BigDecimalDemoUnitTest.java

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+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.math.BigDecimal;
+import java.math.BigInteger;
+import java.math.MathContext;
+import java.math.RoundingMode;
+import java.util.Random;
+
+import org.junit.jupiter.api.Test;
+
+public class BigDecimalDemoUnitTest {
+
+    @Test
+    void test() {
+        System.out.println(BigDecimal.ONE
+            .divide(BigDecimal.valueOf(3), 4, RoundingMode.CEILING)
+            .precision());
+    }
+
+    @Test
+    void whenBigDecimalCreated_thenValueMatches() {
+        BigDecimal bdFromString = new BigDecimal("0.1");
+        BigDecimal bdFromCharArray = new BigDecimal(
+            new char[] { '3', '.', '1', '6', '1', '5' });
+        BigDecimal bdlFromInt = new BigDecimal(42);
+        BigDecimal bdFromLong = new BigDecimal(123412345678901L);
+        BigInteger bigInteger = BigInteger.probablePrime(100, new Random());
+        BigDecimal bdFromBigInteger = new BigDecimal(bigInteger);
+
+        assertEquals("0.1", bdFromString.toString());
+        assertEquals("3.1615", bdFromCharArray.toString());
+        assertEquals("42", bdlFromInt.toString());
+        assertEquals("123412345678901", bdFromLong.toString());
+        assertEquals(bigInteger.toString(), bdFromBigInteger.toString());
+    }
+
+    @Test
+    void whenBigDecimalCreatedFromDouble_thenValueMayNotMatch() {
+        BigDecimal bdFromDouble = new BigDecimal(0.1d);
+        assertNotEquals("0.1", bdFromDouble.toString());
+    }
+
+    @Test
+    void whenBigDecimalCreatedUsingValueOf_thenValueMatches() {
+        BigDecimal bdFromLong1 = BigDecimal.valueOf(123412345678901L);
+        BigDecimal bdFromLong2 = BigDecimal.valueOf(123412345678901L, 2);
+        BigDecimal bdFromDouble = BigDecimal.valueOf(0.1d);
+
+        assertEquals("123412345678901", bdFromLong1.toString());
+        assertEquals("1234123456789.01", bdFromLong2.toString());
+        assertEquals("0.1", bdFromDouble.toString());
+    }
+
+    @Test
+    void whenEqualsCalled_thenSizeAndScaleMatched() {
+        BigDecimal bd1 = new BigDecimal("1.0");
+        BigDecimal bd2 = new BigDecimal("1.00");
+
+        assertFalse(bd1.equals(bd2));
+    }
+
+    @Test
+    void whenComparingBigDecimals_thenExpectedResult() {
+        BigDecimal bd1 = new BigDecimal("1.0");
+        BigDecimal bd2 = new BigDecimal("1.00");
+        BigDecimal bd3 = new BigDecimal("2.0");
+
+        assertTrue(bd1.compareTo(bd3) < 0);
+        assertTrue(bd3.compareTo(bd1) > 0);
+        assertTrue(bd1.compareTo(bd2) == 0);
+        assertTrue(bd1.compareTo(bd3) <= 0);
+        assertTrue(bd1.compareTo(bd2) >= 0);
+        assertTrue(bd1.compareTo(bd3) != 0);
+    }
+
+    @Test
+    void whenPerformingArithmetic_thenExpectedResult() {
+        BigDecimal bd1 = new BigDecimal("4.0");
+        BigDecimal bd2 = new BigDecimal("2.0");
+
+        BigDecimal sum = bd1.add(bd2);
+        BigDecimal difference = bd1.subtract(bd2);
+        BigDecimal quotient = bd1.divide(bd2);
+        BigDecimal product = bd1.multiply(bd2);
+
+        assertTrue(sum.compareTo(new BigDecimal("6.0")) == 0);
+        assertTrue(difference.compareTo(new BigDecimal("2.0")) == 0);
+        assertTrue(quotient.compareTo(new BigDecimal("2.0")) == 0);
+        assertTrue(product.compareTo(new BigDecimal("8.0")) == 0);
+    }
+
+    @Test
+    void whenGettingAttributes_thenExpectedResult() {
+        BigDecimal bd = new BigDecimal("-12345.6789");
+
+        assertEquals(9, bd.precision());
+        assertEquals(4, bd.scale());
+        assertEquals(-1, bd.signum());
+    }
+
+    @Test
+    void whenRoundingDecimal_thenExpectedResult() {
+        BigDecimal bd = new BigDecimal("2.5");
+        // Round to 1 digit using HALF_EVEN
+        BigDecimal rounded = bd
+            .round(new MathContext(1, RoundingMode.HALF_EVEN));
+
+        assertEquals("2", rounded.toString());
+    }
+
+    @Test
+    void givenPurchaseTxn_whenCalculatingTotalAmount_thenExpectedResult() {
+        BigDecimal quantity = new BigDecimal("4.5");
+        BigDecimal unitPrice = new BigDecimal("2.69");
+        BigDecimal discountRate = new BigDecimal("0.10");
+        BigDecimal taxRate = new BigDecimal("0.0725");
+
+        BigDecimal amountToBePaid = BigDecimalDemo
+            .calculateTotalAmount(quantity, unitPrice, discountRate, taxRate);
+
+        assertEquals("10.90", amountToBePaid.toString());
+    }
+}

java-numbers/src/test/java/com/baeldung/maths/BigIntegerDemoUnitTest.java

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+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.math.BigInteger;
+import java.util.Random;
+
+import org.junit.jupiter.api.Test;
+
+public class BigIntegerDemoUnitTest {
+
+    @Test
+    void whenBigIntegerCreatedFromConstructor_thenExpectedResult() {
+        BigInteger biFromString = new BigInteger("1234567890987654321");
+        BigInteger biFromByteArray = new BigInteger(
+            new byte[] { 64, 64, 64, 64, 64, 64 });
+        BigInteger biFromSignMagnitude = new BigInteger(-1,
+            new byte[] { 64, 64, 64, 64, 64, 64 });
+
+        assertEquals("1234567890987654321", biFromString.toString());
+        assertEquals("70644700037184", biFromByteArray.toString());
+        assertEquals("-70644700037184", biFromSignMagnitude.toString());
+    }
+
+    @Test
+    void whenLongConvertedToBigInteger_thenValueMatches() {
+        BigInteger bi = BigInteger.valueOf(2305843009213693951L);
+
+        assertEquals("2305843009213693951", bi.toString());
+    }
+
+    @Test
+    void givenBigIntegers_whentCompared_thenExpectedResult() {
+        BigInteger i = new BigInteger("123456789012345678901234567890");
+        BigInteger j = new BigInteger("123456789012345678901234567891");
+        BigInteger k = new BigInteger("123456789012345678901234567892");
+
+        assertTrue(i.compareTo(i) == 0);
+        assertTrue(j.compareTo(i) > 0);
+        assertTrue(j.compareTo(k) < 0);
+    }
+
+    @Test
+    void givenBigIntegers_whenPerformingArithmetic_thenExpectedResult() {
+        BigInteger i = new BigInteger("4");
+        BigInteger j = new BigInteger("2");
+
+        BigInteger sum = i.add(j);
+        BigInteger difference = i.subtract(j);
+        BigInteger quotient = i.divide(j);
+        BigInteger product = i.multiply(j);
+
+        assertEquals(new BigInteger("6"), sum);
+        assertEquals(new BigInteger("2"), difference);
+        assertEquals(new BigInteger("2"), quotient);
+        assertEquals(new BigInteger("8"), product);
+    }
+
+    @Test
+    void givenBigIntegers_whenPerformingBitOperations_thenExpectedResult() {
+        BigInteger i = new BigInteger("17");
+        BigInteger j = new BigInteger("7");
+
+        BigInteger and = i.and(j);
+        BigInteger or = i.or(j);
+        BigInteger not = j.not();
+        BigInteger xor = i.xor(j);
+        BigInteger andNot = i.andNot(j);
+        BigInteger shiftLeft = i.shiftLeft(1);
+        BigInteger shiftRight = i.shiftRight(1);
+
+        assertEquals(new BigInteger("1"), and);
+        assertEquals(new BigInteger("23"), or);
+        assertEquals(new BigInteger("-8"), not);
+        assertEquals(new BigInteger("22"), xor);
+        assertEquals(new BigInteger("16"), andNot);
+        assertEquals(new BigInteger("34"), shiftLeft);
+        assertEquals(new BigInteger("8"), shiftRight);
+    }
+
+    @Test
+    void givenBigIntegers_whenPerformingBitManipulations_thenExpectedResult() {
+        BigInteger i = new BigInteger("1018");
+
+        int bitCount = i.bitCount();
+        int bitLength = i.bitLength();
+        int getLowestSetBit = i.getLowestSetBit();
+        boolean testBit3 = i.testBit(3);
+        BigInteger setBit12 = i.setBit(12);
+        BigInteger flipBit0 = i.flipBit(0);
+        BigInteger clearBit3 = i.clearBit(3);
+
+        assertEquals(8, bitCount);
+        assertEquals(10, bitLength);
+        assertEquals(1, getLowestSetBit);
+        assertEquals(true, testBit3);
+        assertEquals(new BigInteger("5114"), setBit12);
+        assertEquals(new BigInteger("1019"), flipBit0);
+        assertEquals(new BigInteger("1010"), clearBit3);
+    }
+
+    @Test
+    void givenBigIntegers_whenModularCalculation_thenExpectedResult() {
+        BigInteger i = new BigInteger("31");
+        BigInteger j = new BigInteger("24");
+        BigInteger k = new BigInteger("16");
+
+        BigInteger gcd = j.gcd(k);
+        BigInteger multiplyAndmod = j.multiply(k)
+            .mod(i);
+        BigInteger modInverse = j.modInverse(i);
+        BigInteger modPow = j.modPow(k, i);
+
+        assertEquals(new BigInteger("8"), gcd);
+        assertEquals(new BigInteger("12"), multiplyAndmod);
+        assertEquals(new BigInteger("22"), modInverse);
+        assertEquals(new BigInteger("7"), modPow);
+    }
+
+    @Test
+    void givenBigIntegers_whenPrimeOperations_thenExpectedResult() {
+        BigInteger i = BigInteger.probablePrime(100, new Random());
+
+        boolean isProbablePrime = i.isProbablePrime(1000);
+        assertEquals(true, isProbablePrime);
+    }
+}