Java generic method: Find index of target element in list

Last update on May 19 2025 13:13:07 (UTC/GMT +8 hours)

3. Find Index of Target in Generic List

Write a Java program to create a generic method that takes a list of any type and a target element. It returns the index of the first occurrence of the target element in the list. Return -1 if the target element cannot be found.

Sample Solution:

Java Code:

// FindElement.java
// FindElement Class
import java.util.List;

public class FindElement {

  public static < T > int findIndexOfElement(List < T > list, T target) {
    for (int i = 0; i < list.size(); i++) {
      if (list.get(i).equals(target)) {
        return i;
      }
    }

    return -1;
  }

  public static void main(String[] args) {
    List < Integer > numbers = List.of(1, 2, 3, 4, 5);
    List < String > colors = List.of("Red", "Green", "Blue", "Orange", "White");
    System.out.println("Original list elements:");
    System.out.println("Nums: " + numbers);
    System.out.println("Colors: " + colors);

    int index1 = findIndexOfElement(numbers, 3);
    System.out.println("\nIndex of 3 in numbers: " + index1); // Output: 2

    int index2 = findIndexOfElement(numbers, 6);
    System.out.println("Index of 6 in numbers: " + index2); // Output: -1

    int index3 = findIndexOfElement(colors, "Green");
    System.out.println("Index of \"Green\" in colors: " + index3); // Output: 1

    int index4 = findIndexOfElement(colors, "Black");
    System.out.println("Index of \"Black\" in colors: " + index4); // Output: -1
  }
}

Sample Output:

 Original list elements:
Nums: [1, 2, 3, 4, 5]
Colors: [Red, Green, Blue, Orange, White]

Index of 3 in numbers: 2
Index of 6 in numbers: -1
Index of "Green" in colors: 1
Index of "Black" in colors: -1

Explanation:

In the above exercise, we define a generic method findIndexOfElement() that takes a list list and a target element target as input. With a for loop, the method iterates over the list and checks if each element is equal to the target element. If a match is found, the method returns the index of the first occurrence. If the target element cannot be found, the method returns -1.

In the main() method, we demonstrate the findIndexOfElement() method by passing a list of integers (numbers) and a list of strings (words). We find the index of specific elements in the list and print the results.

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Java program to create a generic method that returns all indices at which a target element occurs in a list.
• Write a Java program to create a generic method that finds the last index of a target element in a list using reverse iteration.
• Write a Java program to create a generic method that employs binary search to return the index of a target element in a sorted list.
• Write a Java program to create a generic method that uses recursion to locate the first occurrence of a target element in a list.

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