Java ArrayList addAll()方法

java.util.ArrayList.addAll(int index, Collection<? extends E> c) 方法追加所有指定集合中的元素到此列表的指定索引位置上。

1 语法

public boolean addAll(int index, Collection<? extends E> c)

2 参数

index：需要插入的索引位置。

c：这是包含要添加到此列表的元素的集合。

3 返回值

如果此列表由于调用而更改，则此方法返回true。

4 示例 

package com.yiidian;

/**
 * 一点教程网： http://www.yiidian.com
 */
/**
 * java.util.ArrayList.addAll(int index, Collection<? extends E> c)方法的例子
 */
import java.util.ArrayList;

public class Demo {
    public static void main(String args[]) {

        // create an empty array list1 with an initial capacity
        ArrayList<Integer> arrlist = new ArrayList<Integer>(5);

        // use add() method to add elements in the list
        arrlist.add(12);
        arrlist.add(20);
        arrlist.add(45);

        // let us print all the elements available in list1
        System.out.println("Printing list1:");
        for (Integer number : arrlist) {
            System.out.println("Number = " + number);
        }

        // create an empty array list2 with an initial capacity
        ArrayList<Integer> arrlist2 = new ArrayList<Integer>(5);

        // use add() method to add elements in list2
        arrlist2.add(25);
        arrlist2.add(30);
        arrlist2.add(31);
        arrlist2.add(35);

        // let us print all the elements available in list2
        System.out.println("Printing list2:");
        for (Integer number : arrlist2) {
            System.out.println("Number = " + number);
        }

        // inserting all elements of list2 at third position
        arrlist.addAll(2, arrlist2);

        System.out.println("Printing all the elements");
        // let us print all the elements available in list1
        for (Integer number : arrlist) {
            System.out.println("Number = " + number);
        }
    }
}

输出结果为：

Printing list1:
Number = 12
Number = 20
Number = 45
Printing list2:
Number = 25
Number = 30
Number = 31
Number = 35
Printing all the elements
Number = 12
Number = 20
Number = 25
Number = 30
Number = 31
Number = 35
Number = 45