Java ArrayList indexOf() Method example

Java.util.ArrayList class method indexOf(Object o) is used for finding out the index of a particular element in a list.

public int indexOf(Object o)

This method returns -1 if the specified element is not present in the list.

Example

package beginnersbook.com;
import java.util.ArrayList;
public class IndexOfExample {
  public static void main(String[] args) {
      ArrayList<String> al = new ArrayList<String>();
      al.add("AB");
      al.add("CD");
      al.add("EF");
      al.add("GH");
      al.add("IJ");
      al.add("KL");
      al.add("MN");

      System.out.println("Index of 'AB': "+al.indexOf("AB"));
      System.out.println("Index of 'KL': "+al.indexOf("KL"));
      System.out.println("Index of 'AA': "+al.indexOf("AA"));
      System.out.println("Index of 'EF': "+al.indexOf("EF"));
  }
}

Output:

Index of 'AB': 0
Index of 'KL': 5
Index of 'AA': -1
Index of 'EF': 2

Reference:

http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html#indexOf(java.lang.Object)