Java - 在 arraylist 的两个元素之间添加一个元素

Question

i want to add an element between two other elements in an arraylist like:

Element 1
Element 2
Element 3

Adding an element:

Element 1
Element 4 <---- Adding element 4 between 1 and 2.
Element 2
Element 3

Is this possible?

Answer 1

Yes - you want the overload of add that takes an index . In this case, the index would be 1:

list.add(1, 4); // Index then value

Note that adding an element involves copying all existing elements after that (so values 2 and 3 in your example), so if you do this a lot with a very large list, it can have performance implications.

Answer 2

Simple as that:

myList.add(1, "Element 4"); 

See this documentation for further details.

Answer 3

Yes, you can use the add() method of ArrayList to insert an element at any particular index.

Assuming the name of your ArrayList is list, you can add 4 at index 1 in this manner-

list.add(1, 4);

The first parameter takes the index and the second parameter takes the value of the element you want to insert.