List: int indexOf(Object x) Returns the index of the first occurrence of x, or -1 if the List does not contain x. : List « Utility Classes « SCJP

import java.util.ArrayList;
import java.util.List;

public class MainClass {
  public static void main(String[] argv) {

    List<String> list = new ArrayList<String>();
    list.add("a");
    list.add("b");
    list.add("c");

    System.out.println(list.indexOf("a"));

  }
}

8.13.List
	8.13.1.	A List keeps it elements in the order in which they were added.
	8.13.2.	List: void add(int index, Object x) Inserts x at index.
	8.13.3.	List: Object get(int index) Returns the element at index.
	8.13.4.	List: int indexOf(Object x) Returns the index of the first occurrence of x, or -1 if the List does not contain x.
	8.13.5.	Collection: Object remove(int index) Removes the element at index.
	8.13.6.	ListIterator extends the Iterator interface to support bidirectional iteration of lists.
	8.13.7.	Using Iterator for Lists
	8.13.8.	toArray() method