Programming in Java: Arrays and Array Lists. Last delivered in 2013. All educational material listed or linked to on these pages in relation to King's College London may be provided for reference only, and therefore does not necessarily reflect the current course content.

1. ARRAYS AND ARRAY
LISTS
Martin Chapman
martin.chapman@kcl.ac.uk

2. What?
1 56 goat
dog 34 cat

3. What?
1 56 goat
dog 34 cat
number1 number2
number3
string1
string2 string3

4. 34
number3
What?
1 56
goat dog cat
number1 number2
string1 string2 string3

5. 34
number3
What?
1 56
goat dog cat
number1 number2
string1 string2 string3

6. 34
What?
1 56
goat dog cat
numbers
strings

7. 34
What?
1 56
goat dog cat
numbers
strings
0 1 2
0 1 2

8. Why?

9. Why?
fish
product1
Make a new variable called
product1.
Add fish information to it.

10. Why?
fish
product1
steak
product2

11. Why?
fish
product1
steak
product2
lamb
product3

12. Why?
fish
product1
steak
product2
lamb
product3
How can I tell what is in my basket
without directly referencing each
variable name?

13. Why?
fish
product1
steak
product2
lamb
product3
How can I tell what is in my basket
without directly referencing each
variable name?
I can’t (in a reasonable amount of code).
For a basket of 200 products, calculating
the total bill would take lots of code.

14. Why?
products
0 1 2

15. Why?
fish
products
0 1 2

16. Why?
fish steak
products
0 1 2

17. Why?
fish steak lamb
products
0 1 2

18. Why?
fish steak lamb
products
0 1 2
I can now write a short piece of code
which looks at the first item in the list, then
the second, third etc. until the end, and
calculates the total bill. In this process only
one variable is referenced.
This is an array.

19. How?
products
0 1 2
data type
3 ‘slots’ in
memory

20. How?
products
0 1 2
fish steak lamb
name[index]

21. How?
i is the index
to the array
array length

22. •When we declare a new array, we have to give it a
fixed size.
•This means that, aside from manually expanding the
size of the array in memory, we cannot have a list
which holds an arbitrary number of items.
•To address this issue, we introduce array lists.
•Array lists perform exactly the same
operations as an array, but their syntax is
different.

23. How?
data type
3 ‘slots’ in
memory
class object

24. How?
name[index]
object.method()
0
1
2

25. How?
object.get(index)
object.size()

26. SUMMARY
• Arrays allow us to store lists of related items so that we can
access them more efficiently.
• As Arrays are of a fixed size, we also rely on ArrayLists, the
size of which can expand as necessary.
• Although the syntax of an ArrayList is different, we can still
carry out the same operations.

27. SUMMARY
• This is the very bare bones of Arrays and ArrayLists.
• For everything you need to know, you should consult the
lecture notes, SGTs and labs.