Learn Java
Lists
Lists are an interface from the Java Collections Framework
Lists are ordered sequences of items. Each item has a position in the list (an index) starting from zero, and items can be inserted, added and removed from the list
Lists can have duplicate entries and can also if necessary have a natural ordering such as alphabetical
Lists are homogeneous - all the elements have to be of the same type
Lists are a subinterface of the Collection interface
The table below shows some methods of the Collection interface
| Method | Description |
|---|---|
| addAll(Collection c) | Adds all the elements of the specified collection to the receiver |
| add(E o) | Adds the specified element to the collection |
| remove(Object o) | Remove the specified element from the collection |
| clear() | Removes all elements from the collection |
| size() | Returns the number of elements in the collection |
| contains(Object o) | Returns true if the collection contains the specified element |
| isEmpty() | Returns true if the collection is empty |
List can implement all of the methods of the Collection interface because List is a subinterface of the Collection interface
So to create a list containing instances of the Car class we could use the following statement
List<Car> myCarList = new ArrayList<Car>();
List is the interface, ArrayList is a class that implements the List interface and the element type is placed between the angled brackets, in this case instances of the class Car
We can add elements to our car list and print the size as follows
List<Car> myCarList = new ArrayList<Car>();
myCarList.add("VW Golf");
myCarList.add("Peugot 206");
myCarList.add("BMW 525");
System.out.println(myCarList.size());
Elements can also be inserted into a list at a specified index as follows
myCarList.add(2, "Ford Capri");
This will move "BMW 525" up one in the list to index 3
We can also get the element at a specific index and place the value into a variable as follows
String selectedCar = myCarList.get(1);
In a similar way we can remove an element from the list as follows
String removedCar - myCarList.remove(2);
We may need to find the index of a specific element, we can find the first occurrence of the element (should there be duplicates) as follows
int firstPosition = myCarList.indexOf("VW Golf");
To find the last occurrence of the element in the list use a statement similar to the following
int lastPosition = myCarList.lastIndexOf("VW Golf");
To replace an element in a list do something like the following
myCarList.set(1, "Fiat Punto");
We can interate through a list as follows
for (String eachElement : myCarList)
{
System.out.println(eachElement);
}
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