Skip to content

List Methods

layout: default title: List Method

We have seen several List methods already:

  • int size() - get the number of elements in the List.
  • boolean add(element) - add to the end of the List.
  • void add(index, element) - insert an element at the specified index.
  • E get(index) - get element at index.
  • E set(index, element) - replace an existing element.
  • E remove(index) - remove an element at index.

List defines other useful methods.

boolean contains(Object)

This method iterates through the List, returning true if the Object is in the List.

  • The method calls the Object's .equals(Object) method to compare the Object to each element.
  • We can pass any Object to this method, just like we can pass any Object to .equals(Object).

int indexOf(Object)

Returns the index of the first occurrence of the specified Object in this List, or -1 if this List does not contain the element. * This is like contains(Object) in that we can pass any Object, and the method calls .equals(Object) on the Object to compare it to each element.

boolean remove(Object o)

This overloaded remove method will remove the first occurrence of an Object from the List. * It also calls .equals(Object) to determine which element to remove. * It returns true if the Object was in the List. * It does not return an Object reference because if you are passing in a reference, you already have the reference you need.

boolean isEmpty()

Returns true if this list contains no elements.

boolean addAll(Collection c)

  • Add the contents of the given collection to the end of the list.

List subList(int start, int stop)

  • Return a new list of the elements from index start (inclusive) up to but not including the element at index stop, or to the last element if stop is the size of the list.

boolean equals(Object o)

  • This standard method inherited from Object is overridden for List so that it returns true if Object o is also a list of the same size, and each pair of corresponding elements are .equals().

Practice Exercise

List implementation classes such as ArrayList, LinkedList, and Vector actually inherit the implementations of some methods from the superclasses they extend. Most also implement additional interfaces beyond List.

List hierarchy

Drill

ListInterface/com.example.listinterface.drills.PlanetList

  • Run the program to see what Planets are already in the List of Planets.

  • Follow the instructions in comments to use some of the above methods on the planets List.

Prev -- Up -- Next