简单的add()方法用于在列表的末尾添加元素，但是add方法的另一种变体用于向指定的索引添加元素。
public void add(int index, Object element)
此方法在给定索引处添加元素。
例
package beginnersbook.com;import java.util.ArrayList;public class AddMethodExample { public static void main(String[] args) { // ArrayList of String type ArrayList<String> al = new ArrayList<String>(); // simple add() methods for adding elements at the end al.add("Hi"); al.add("hello"); al.add("String"); al.add("Test"); //adding element to the 4th position //4th position = 3 index as index starts with 0 al.add(3,"Howdy"); System.out.println("Elements after adding string Howdy:"+ al); //adding string to 1st position al.add(0, "Bye"); //Print System.out.println("Elements after adding string bye:"+ al); }}
输出：
Elements after adding string Howdy:[Hi, hello, String, Howdy, Test]Elements after adding string bye:[Bye, Hi, hello, String, Howdy, Test]
