Replacing Inserting Removing

We can do more than just add to the end of a list with add(E), or see what is at an index with get(index).

We can change what is in the ArrayList.

E set(index, E) to Replace

This method replaces the current item at an index...

and returns the object reference that was there (just in case we want to use it).

ArrayList<String> strList = new ArrayList<String>();
strList.add("Alice");
strList.add("Mad Hatter");

String oldStr = strList.set(1, "Cheshire Cat");
System.out.println(oldStr);   // Mad Hatter

void add(index, E) to Insert

This method adds the element at the given index...

and shifts any other objects one space lower in the list. * Think of it like an insert.

strList.add(0, "Queen of Hearts");

E remove(index) to Delete

This method removes the object at the given index...

and returns it (just in case we want to use it)...

and shifts all subsequent elements up one spot.

String removed = strList.remove(1);
System.out.println(removed); // Alice

The size of the ArrayList decreases by one - there is no empty space at the end.

Drill

GenericsAndArrayList/com.example.generics.drills.ChangingArrayList

• In this drill you will follow steps to change the contents of an ArrayList<String>.
• After each change, you will print out the entire list with System.out.println.
• When all changes are correct, a message prints after the list output.

Practice Exercise

ArrayList has a nice toString(), which iterates through the elements of the list and calls each object's toString() method.

As we have seen, a regular array does not have a nice toString().

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