Added a new feature to convert numbers into their word representation

src/main/java/com/thealgorithms/conversions/NumberToWords.java

@@ -0,0 +1,100 @@
+package com.thealgorithms.conversions;
+
+import java.math.BigDecimal;
+
+/**
+ A Java-based utility for converting numeric values into their English word
+ representations. Whether you need to convert a small number, a large number
+ with millions and billions, or even a number with decimal places, this utility
+ has you covered.
+ *
+ */
+public class NumberToWords {
+
+    private NumberToWords() {
+    }
+
+    private static final String[] units = {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
+
+    private static final String[] tens = {"", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};
+
+    private static final String[] powers = {"", "Thousand", "Million", "Billion", "Trillion"};
+
+    private static final String ZERO = "Zero";
+    private static final String POINT = " Point";
+    private static final String NEGATIVE = "Negative ";
+
+    public static String convert(BigDecimal number) {
+        if (number == null) {
+            return "Invalid Input";
+        }
+
+        // Check for negative sign
+        boolean isNegative = number.signum() < 0;
+
+        // Split the number into whole and fractional parts
+        BigDecimal[] parts = number.abs().divideAndRemainder(BigDecimal.ONE);
+        BigDecimal wholePart = parts[0]; // Keep whole part as BigDecimal
+        String fractionalPartStr = parts[1].compareTo(BigDecimal.ZERO) > 0 ? parts[1].toPlainString().substring(2) : ""; // Get fractional part only if it exists
+
+        // Convert whole part to words
+        StringBuilder result = new StringBuilder();
+        if (isNegative) {
+            result.append(NEGATIVE);
+        }
+        result.append(convertWholeNumberToWords(wholePart));
+
+        // Convert fractional part to words
+        if (!fractionalPartStr.isEmpty()) {
+            result.append(POINT);
+            for (char digit : fractionalPartStr.toCharArray()) {
+                int digitValue = Character.getNumericValue(digit);
+                result.append(" ").append(digitValue == 0 ? ZERO : units[digitValue]);
+            }
+        }
+
+        return result.toString().trim();
+    }
+
+    private static String convertWholeNumberToWords(BigDecimal number) {
+        if (number.compareTo(BigDecimal.ZERO) == 0) {
+            return ZERO;
+        }
+
+        StringBuilder words = new StringBuilder();
+        int power = 0;
+
+        while (number.compareTo(BigDecimal.ZERO) > 0) {
+            // Get the last three digits
+            BigDecimal[] divisionResult = number.divideAndRemainder(BigDecimal.valueOf(1000));
+            int chunk = divisionResult[1].intValue();
+
+            if (chunk > 0) {
+                String chunkWords = convertChunk(chunk);
+                if (power > 0) {
+                    words.insert(0, powers[power] + " ");
+                }
+                words.insert(0, chunkWords + " ");
+            }
+
+            number = divisionResult[0]; // Continue with the remaining part
+            power++;
+        }
+
+        return words.toString().trim();
+    }
+
+    private static String convertChunk(int number) {
+        String chunkWords;
+
+        if (number < 20) {
+            chunkWords = units[number];
+        } else if (number < 100) {
+            chunkWords = tens[number / 10] + (number % 10 > 0 ? " " + units[number % 10] : "");
+        } else {
+            chunkWords = units[number / 100] + " Hundred" + (number % 100 > 0 ? " " + convertChunk(number % 100) : "");
+        }
+
+        return chunkWords;
+    }
+}

src/test/java/com/thealgorithms/conversions/NumberToWordsTest.java

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+package com.thealgorithms.conversions;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.math.BigDecimal;
+import org.junit.jupiter.api.Test;
+
+public class NumberToWordsTest {
+
+    @Test
+    void testNullInput() {
+        assertEquals("Invalid Input", NumberToWords.convert(null), "Null input should return 'Invalid Input'");
+    }
+
+    @Test
+    void testZeroInput() {
+        assertEquals("Zero", NumberToWords.convert(BigDecimal.ZERO), "Zero input should return 'Zero'");
+    }
+
+    @Test
+    void testPositiveWholeNumbers() {
+        assertEquals("One", NumberToWords.convert(BigDecimal.ONE), "1 should convert to 'One'");
+        assertEquals("One Thousand", NumberToWords.convert(new BigDecimal("1000")), "1000 should convert to 'One Thousand'");
+        assertEquals("One Million", NumberToWords.convert(new BigDecimal("1000000")), "1000000 should convert to 'One Million'");
+    }
+
+    @Test
+    void testNegativeWholeNumbers() {
+        assertEquals("Negative One", NumberToWords.convert(new BigDecimal("-1")), "-1 should convert to 'Negative One'");
+        assertEquals("Negative One Thousand", NumberToWords.convert(new BigDecimal("-1000")), "-1000 should convert to 'Negative One Thousand'");
+    }
+
+    @Test
+    void testFractionalNumbers() {
+        assertEquals("Zero Point One Two Three", NumberToWords.convert(new BigDecimal("0.123")), "0.123 should convert to 'Zero Point One Two Three'");
+        assertEquals("Negative Zero Point Four Five Six", NumberToWords.convert(new BigDecimal("-0.456")), "-0.456 should convert to 'Negative Zero Point Four Five Six'");
+    }
+
+    @Test
+    void testLargeNumbers() {
+        assertEquals("Nine Hundred Ninety Nine Million Nine Hundred Ninety Nine Thousand Nine Hundred Ninety Nine", NumberToWords.convert(new BigDecimal("999999999")), "999999999 should convert correctly");
+        assertEquals("One Trillion", NumberToWords.convert(new BigDecimal("1000000000000")), "1000000000000 should convert to 'One Trillion'");
+    }
+
+    @Test
+    void testNegativeLargeNumbers() {
+        assertEquals("Negative Nine Trillion Eight Hundred Seventy Six Billion Five Hundred Forty Three Million Two Hundred Ten Thousand Nine Hundred Eighty Seven", NumberToWords.convert(new BigDecimal("-9876543210987")), "-9876543210987 should convert correctly");
+    }
+
+    @Test
+    void testFloatingPointPrecision() {
+        assertEquals("One Million Point Zero Zero One", NumberToWords.convert(new BigDecimal("1000000.001")), "1000000.001 should convert to 'One Million Point Zero Zero One'");
+    }
+
+    @Test
+    void testEdgeCases() {
+        assertEquals("Negative Zero", NumberToWords.convert(new BigDecimal("-0.0")), "-0.0 should convert to 'Negative Zero'");
+        assertEquals("Zero Point Zero Zero Zero Zero Zero Zero One", NumberToWords.convert(new BigDecimal("1E-7")), "1E-7 should convert to 'Zero Point Zero Zero Zero Zero Zero Zero One'");
+    }
+}