Arraylist lastIndexOf() Method in Java with Examples (original) (raw)

Last Updated : 10 Dec, 2024

In Java, the **lastIndexOf() method is used to find the index of the last occurrence of a specified element in an ArrayList.

**Example 1: Here, we will use the **lastIndexOf() method **to find the index of the last occurrence of a specific element in an ArrayList of integers.

Java `

// Java program to demonstrate the use of // lastIndexOf() method with Integers import java.util.ArrayList;

public class GFG { public static void main(String[] args) {

    // Creating an ArrayList of Integers
    ArrayList<Integer> n = new ArrayList<>();

    // Adding elements to the ArrayList
    n.add(21);
    n.add(22);
    n.add(23);

    // Using lastIndexOf() to find the last index of 20
    int i= n.lastIndexOf(22);
    
    System.out.println("The last index of 22 is: " + i);
}

}

Output

The last index of 22 is: 1

Syntax of ArrayList `lastIndexOf()` Method

public int lastIndexOf(Object o)

**Parameter: The object o whose last index is to be returned.
**Return Type: It returns the last occurrence of the element passed in the parameter. It returns -1 if the element is not found.

**Example 2: Here, we use the **lastIndexOf() method **to find the last occurrence of an element in an ArrayList of **strings.

Java `

// Java program to demonstrate the use of // lastIndexOf() method for Strings import java.util.ArrayList;

public class GFG { public static void main(String[] args) {

    // Creating an ArrayList of Strings
    ArrayList<String> f = new ArrayList<>();

    // Adding elements to the ArrayList
    f.add("Apple");
    f.add("Banana");
    f.add("Orange");

    // Using lastIndexOf() to find the 
    // last index of "Orange"
    int i = f.lastIndexOf("Orange");

    System.out.println("The last index of Orange is: " + i);
}

}

Output

The last index of Orange is: 2

**Example 3: In this example, we will use the **lastIndexOf() method with an ArrayList of custom objects. Here, we will **find the last index of a specific object in the list.

Java `

// Java program to demonstrate the use of // lastIndexOf() method with custom Objects import java.util.ArrayList;

class Person { String n; int a;

// Constructor to initialize Person object
public Person(String n, int a) {
    this.n = n;
    this.a = a;
}

// Overriding equals() to compare Person 
// objects based on name and age
@Override
public boolean equals(Object o) {
    if (this == o) 
      return true;
    if (o == null || getClass() != o.getClass()) 
      return false;
    Person p = (Person) o;
    return a == p.a && n.equals(p.n);
}

}

public class Main { public static void main(String[] args) {

    // Creating an ArrayList of Person objects
    ArrayList<Person> p = new ArrayList<>();

    // Adding elements to the ArrayList
    p.add(new Person("Sweta", 24));
    p.add(new Person("Amiya", 27));
    p.add(new Person("Gudly", 23));

    // Using lastIndexOf() to find the 
    // last index of a Person object
    Person personToFind = new Person("Sweta", 24);
    int i = p.lastIndexOf(personToFind);

    System.out.println("The last index of Sweta is: " + i);
}

}

Output

The last index of Sweta is: 0

Arraylist lastIndexOf() Method in Java with Examples (original) (raw)

Syntax of ArrayList lastIndexOf() Method

Syntax of ArrayList `lastIndexOf()` Method