Java Arraylist indexOf() Method

// Java program to demonstrate the  // use of indexOf() method import java.util.ArrayList; public class GFG {  public static void main(String[] args) {    // Creating an ArrayList of Integers  ArrayList<Integer> arr = new ArrayList<Integer>(5);  // Adding elements to the ArrayList  arr.add(1);  arr.add(2);  arr.add(3);  // Printing the initial values   // in the ArrayList  System.out.print("");  for (Integer v : arr) {  System.out.print(v + " ");  }   // Using indexOf() to   // find the index of 3  int p = arr.indexOf(3);  // Prints the index of the element  System.out.println("\nThe element 3 is at index: " + p);  } } 

// Java program to demonstrate the use of  // indexOf() and lastIndexOf() methods import java.util.ArrayList; public class GFG {  public static void main(String[] args) {    // Creating an ArrayList of Integers  ArrayList<Integer> arr = new ArrayList<Integer>(6);  // Adding elements to the ArrayList  arr.add(1);  arr.add(2);  arr.add(4);  arr.add(6);  arr.add(5);  arr.add(2);  // Using indexOf() to find the   // first index of 4  int p1 = arr.indexOf(4);    // Using lastIndexOf() to find the   // last index of 4  int p2 = arr.lastIndexOf(4);    // Balancing the 0-based indexing  p1 = p1 + 1;  p2 = p2 + 1;    // Printing first and last index of 4  System.out.println("The first occurrence of 4 is: " + p1);  System.out.println("The last occurrence of 4 is: " + p2);  } } 

// Java program to demonstrate the use of  // indexOf() method with a non-existent element import java.util.ArrayList; public class GFG {  public static void main(String[] args) {    // Creating an ArrayList of Integers  ArrayList<Integer> arr = new ArrayList<Integer>(5);  // Adding elements to the ArrayList  arr.add(10);  arr.add(20);  arr.add(30);  // Trying to find the index of   // a non-existent element  int p = arr.indexOf(50);  System.out.println("The index of 50 is: " + p);  } }