Java ArrayList.indexOf() Method

public int indexOf(Object o)

The indexOf() method is used to get the index of the first occurrence of an element in an ArrayList object.

Package: java.util

Java Platform: Java SE 8

Syntax:

indexOf(Object o)

Parameters:

Return Value:
The index of the first occurrence an element in ArrayList, or -1 if the element does not exist.

Return Value Type: int

Pictorial presentation of ArrayList.indexOf() Method

Example: ArrayList.indexOf Method

The following example creates an ArrayList containing various colors. It then tries to determine the position of a certain color.

import java.util.*;

public class test {
   public static void main(String[] args) {
      
    // create an empty array list with an initial capacity
    ArrayList<String> color_list = new ArrayList<String>(5);

    // use add() method to add values in the list
    color_list.add("White");
    color_list.add("Black");
    color_list.add("Red");
    color_list.add("Green");
	color_list.add("Yellow");
	
    System.out.println("Size of list: " + color_list.size());

    // Print the colors in the list
    for (String value : color_list) {
      System.out.println("Value = " + value);
    }  

    // Get the index of element "White"
	 int pos=color_list.indexOf("White");
    System.out.println("The color White is at index " + pos);
	
	 // Get the index of element "Green"
    pos=color_list.indexOf("Green");
    System.out.println("The color Green is at index " + pos);
  }
}
   

Output :

F:\java>javac test.java
F:\java>java test
  Size of list: 5
  Value = White
  Value = Black
  Value = Red
  Value = Green
  Value = Yellow
  The color White is at index 0
  The color Green is at index 3 

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