How to Get the Index of a Specified Element in an Array in Java?
In Java, to find the index of a specific element in an array, we can iterate through it and checking each element. There are several ways to achieve this, including using loops, utility functions, Arrays.asList() for non-primitive arrays, and Streams.
Example: The simplest way is to iterate through the array with a for loop and compare each element to the target.
// Java Program to get the Index of
// Specified Element in an Array
public class FindIndex {
public static void main(String[] args) {
int[] n = {1, 2, 3, 4, 5};
int t = 3;
for (int i = 0; i < n.length; i++) {
// Check if the current element
// matches the target
if (n[i] == t) {
System.out.println("Element found at index: " + i);
return;
}
}
System.out.println("Element not found in the array.");
}
}
Output
Element found at index: 2
Other Methods to Get the Index of a Specified Element
1. Using a Utility Function
Encapsulating the logic in a utility function improves code reusability and readability. This method allows us to check the index of any target element in an array.
// Java Program to get the Index of Specified Element
// in an Array using a Utility Function
public class FindIndex {
public static int getIndex(int[] arr, int t) {
if (arr != null) {
for (int i = 0; i < arr.length; i++) {
if (arr[i] == t) {
return i; // Return index if element is found
}
}
}
return -1; // Return -1 if element is not found
}
public static void main(String[] args) {
int[] n = {1, 2, 3, 4, 5};
int t = 3;
int i = getIndex(n, t);
if (i != -1) {
System.out.println("Element found at index: " + i);
} else {
System.out.println("Element not found.");
}
}
}
Output
Element found at index: 2
Note: if (arr != null), this ensures the array is not null to avoid a NullPointerException.
2. Using Arrays.asList() for Object Arrays
For arrays of non-primitive types (like String or Integer), Arrays.asList() can be used to convert the array into a list. The indexOf() method of the list is then used to find the element's index.
// Java Program to get the Index of Specified Element
// in an Array using Arrays.asList()
import java.util.Arrays;
public class FindIndex {
public static void main(String[] args) {
String[] n = {"Alice", "Bob", "Charlie", "David"};
String t = "Charlie";
int i = Arrays.asList(n).indexOf(t); // Get index of target element
if (i != -1) {
System.out.println("Element found at index: " + i);
} else {
System.out.println("Element not found.");
}
}
}
Output
Element found at index: 2
Explanation: The Arrays.asList(names) converts the array to a List. It works only for object arrays. The indexOf(target) returns the index of the first occurrence of the target in the list or -1 if not found.
3. Using Streams (Java 8+)
Streams can be useful for advanced scenarios where we need to filter or process elements while finding the index.
// Java Program to get the Index of Specified Element
// in an Array using Streams
import java.util.stream.IntStream;
public class FindIndex {
public static void main(String[] args) {
int[] n = {1, 2, 3, 4, 5};
int t = 3;
int ind = IntStream.range(0, n.length) // Create a range of indices
.filter(i -> n[i] == t) // Filter matching indices
.findFirst() // Get the first match
.orElse(-1); // Default to -1 if not found
if (ind != -1) {
System.out.println("Element found at index: " + ind);
} else {
System.out.println("Element not found.");
}
}
}
Output
Element found at index: 2
Explanation: The .filter(i -> numbers[i] == target) filters indices, where the element matches the target. The .findFirst() returns the first matching index if any. The .orElse(-1) provides a default value (-1) if no match is found.
When to Use Which Method
- Use for loop for simple and effective for basic needs.
- Use utility function to improve code reuse and readability.
Arrays.asList()for non-primitive arrays is efficient for object arrays.- Use Streams for more advanced and functional programming approaches.
