如何在数组列表中的特定位置插入对象

To insert value into ArrayList at particular index, use:

public void add(int index, E element)

This method will shift the subsequent elements of the list. but you can not guarantee the List will remain sorted as the new Object you insert may sit on the wrong position according to the sorting order.

To replace the element at the specified position, use:

public E set(int index, E element)

This method replaces the element at the specified position in the list with the specified element, and returns the element previously at the specified position.

Actually the way to do it on your specific question is arrayList.add(1,"INSERTED ELEMENT"); where 1 is the position

Here is the simple arraylist example for insertion at specific index

ArrayList<Integer> str=new ArrayList<Integer>();
str.add(0);
str.add(1);
str.add(2);
str.add(3);
//Result = [0, 1, 2, 3]
str.add(1, 11);
str.add(2, 12);
//Result = [0, 11, 12, 1, 2, 3]

Note that when you insert into a List at a position, you are really inserting at a dynamic position within the List's current elements. See here:

http://tpcg.io/0KmArS

package com.tutorialspoint;


import java.util.ArrayList;


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


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


// use add() method to add elements in the list
arrlist.add(15, 15);
arrlist.add(22, 22);
arrlist.add(30, 30);
arrlist.add(40, 40);


// adding element 25 at third position
arrlist.add(2, 25);


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

$javac com/tutorialspoint/ArrayListDemo.java

$java -Xmx128M -Xms16M com/tutorialspoint/ArrayListDemo

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 15, Size: 0
at java.util.ArrayList.rangeCheckForAdd(ArrayList.java:661)
at java.util.ArrayList.add(ArrayList.java:473)
at com.tutorialspoint.ArrayListDemo.main(ArrayListDemo.java:12)

From Oracle Official Documentation

This method Appends the specified element to the end of this list.

add(E e) //append element to the end of the arraylist.

This method Inserts the specified element at the specified position in this list.

void add(int index, E element) //inserts element at the given position in the array list.

This method Replaces the element at the specified position in this list with the specified element.

set(int index, E element) //Replaces the element at the specified position in this list with the specified element.
      



      

You must handle ArrayIndexOutOfBounds by yourself when adding to a certain position.

For convenience, you may use this extension function in Kotlin

/**
* Adds an [element] to index [index] or to the end of the List in case [index] is out of bounds
*/
fun <T> MutableList<T>.insert(index: Int, element: T) {
if (index <= size) {
add(index, element)
} else {
add(element)
}
}