[integer-to-digits] How to Split an Integer Number Into Digits in Java (#14736)

core-java-modules/core-java-numbers-6/src/test/java/com/baeldung/integertodigits/IntegerToDigitsUnitTest.java

@@ -0,0 +1,67 @@
+package com.baeldung.integertodigits;
+
+import com.google.common.collect.Lists;
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class IntegerToDigitsUnitTest {
+    private final static int THE_NUMBER = 1230456;
+    private final static List<Integer> EXPECTED_INT_LIST = Lists.newArrayList(1, 2, 3, 0, 4, 5, 6);
+    private final static String[] EXPECTED_STR_ARRAY = new String[] { "1", "2", "3", "0", "4", "5", "6" };
+    private final static List<String> EXPECTED_STR_LIST = Lists.newArrayList("1", "2", "3", "0", "4", "5", "6");
+    private final static char[] EXPECTED_CHAR_ARRAY = new char[] { '1', '2', '3', '0', '4', '5', '6' };
+
+    @Test
+    void whenUsingModOperator_thenGetExpectedResult() {
+        int number = THE_NUMBER;
+        LinkedList<Integer> result = new LinkedList<>();
+        while (number > 0) {
+            result.push(number % 10);
+            number /= 10;
+        }
+        assertEquals(EXPECTED_INT_LIST, result);
+    }
+
+
+    private void collectDigits(int num, List<Integer> digitList) {
+        if (num / 10 > 0) {
+            collectDigits(num / 10, digitList);
+        }
+        digitList.add(num % 10);
+    }
+
+    @Test
+    void whenUsingModOperatorAndRecursion_thenGetExpectedResult() {
+        List<Integer> result = new ArrayList<>();
+        collectDigits(THE_NUMBER, result);
+        assertEquals(EXPECTED_INT_LIST, result);
+    }
+
+    @Test
+    void whenUsingIntStream_thenGetExpectedResult() {
+        String numStr = String.valueOf(THE_NUMBER);
+        List<Integer> result = numStr.chars().map(Character::getNumericValue).boxed().collect(Collectors.toList());
+        assertEquals(EXPECTED_INT_LIST, result);
+    }
+
+    @Test
+    void whenUsingToCharArray_thenGetExpectedResult() {
+        String numStr = String.valueOf(THE_NUMBER);
+        char[] result = numStr.toCharArray();
+        assertArrayEquals(EXPECTED_CHAR_ARRAY, result);
+    }
+
+    @Test
+    void whenUsingSplit_thenGetExpectedResult() {
+        String numStr = String.valueOf(THE_NUMBER);
+        String[] result = numStr.split("(?<=.)");
+        assertArrayEquals(EXPECTED_STR_ARRAY, result);
+    }
+}