BAEL-6327 - Find the index of an element in a Java array (#13844)

core-java-modules/core-java-arrays-operations-basic/src/main/java/com/baeldung/arrayindex/ArrayIndex.java

@@ -0,0 +1,28 @@
+package com.baeldung.arrayindex;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.IntStream;
+
+class ArrayIndex {
+    static int forLoop(int[] numbers, int target) {
+        for (int index = 0; index < numbers.length; index++) {
+            if (numbers[index] == target) {
+                return index;
+            }
+        }
+        return -1;
+    }
+
+    static int listIndexOf(Integer[] numbers, int target) {
+        List<Integer> list = Arrays.asList(numbers);
+        return list.indexOf(target);
+    }
+
+    static int intStream(int[] numbers, int target) {
+        return IntStream.range(0, numbers.length)
+          .filter(i -> numbers[i] == target)
+          .findFirst()
+          .orElse(-1);
+    }
+}

core-java-modules/core-java-arrays-operations-basic/src/test/java/com/baeldung/arrayindex/ArrayIndexUnitTest.java

@@ -0,0 +1,106 @@
+package com.baeldung.arrayindex;
+
+import static com.baeldung.arrayindex.ArrayIndex.forLoop;
+import static com.baeldung.arrayindex.ArrayIndex.intStream;
+import static com.baeldung.arrayindex.ArrayIndex.listIndexOf;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.Arrays;
+
+import org.apache.commons.lang3.ArrayUtils;
+import org.junit.jupiter.api.Test;
+
+import com.google.common.primitives.Ints;
+
+class ArrayIndexUnitTest {
+
+    @Test
+    void givenIntegerArray_whenUseForLoop_thenWillGetElementIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(2, forLoop(numbers, 30));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseForLoop_thenWillGetElementMinusOneIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(-1, forLoop(numbers, 100));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseIndexOf_thenWillGetElementIndex() {
+        Integer[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(2, listIndexOf(numbers, 30));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseIndexOf_thenWillGetElementMinusOneIndex() {
+        Integer[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(-1, listIndexOf(numbers, 100));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseIntStream_thenWillGetElementIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(2, intStream(numbers, 30));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseIntStream_thenWillGetElementMinusOneIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(-1, intStream(numbers, 100));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseBinarySearch_thenWillGetElementIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(2, Arrays.binarySearch(numbers, 30));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseBinarySearch_thenWillGetUpperBoundMinusIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(-6, Arrays.binarySearch(numbers, 100));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseBinarySearch_thenWillGetInArrayMinusIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(-2, Arrays.binarySearch(numbers, 15));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseBinarySearch_thenWillGetLowerBoundMinusIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(-1, Arrays.binarySearch(numbers, -15));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseApacheCommons_thenWillGetElementIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(2, ArrayUtils.indexOf(numbers, 30));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseApacheCommonsStartingFromIndex_thenWillGetNegativeIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(-1, ArrayUtils.indexOf(numbers, 30, 3));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseApacheCommons_thenWillGetElementMinusOneIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(-1, ArrayUtils.indexOf(numbers, 100));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseGuavaInts_thenWillGetElementIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(2, Ints.indexOf(numbers, 30));
+    }
+
+    @Test
+    void givenIntegerArray_whenUseGuavaInts_thenWillGetElementMinusOneIndex() {
+        int[] numbers = { 10, 20, 30, 40, 50 };
+        assertEquals(-1, Ints.indexOf(numbers, 100));
+    }
+}