Data collections

Android Club 2015

Agenda

• Array• ArrayList• HashMap

Array

• Array is container object that holds a fixed number of values of a single type

Why we need array?

• We need array to store list of data in one object

When to use array?

• When you know exact number of data in list

• When all data in the same data type

int array: example

int[] numbers = {3, 6, 9};System.out.println(numbers[0]);

int array: practice

• Create array of numbers: from 1 to 10• Print 3rd number• Print 6th number• Print 9th number

String array: example

String[] weekdays = {"Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"};System.out.println(weekdays[1]);

String array: practice

• Create array of strings: months• Print June using array

boolean array: example

boolean[] isOrel = {true, false, false};System.out.println(isOrel[1]);

boolean array: practice

• Create boolean array: isReshka• Size: 5• Print 4th value

char array: example

char[] letters = {'a', 'b', 'c'};System.out.println(letters[1]);

char array: practice

• Create char array: alphabet• Print 10th letter• Print 20th letter

Empty array: example

• String[] names = new String[3];• names[0]="Vadim";• names[1]="Jonik";• names[2]="Timur";• System.out.println(names[1]);

Empty array: practice

• Create empty String array: fruit• Size: 4• 0 – Apple• 1 – Pineapple• 2 – Banana• 3 - Kiwi

Array length: example

int[] letters = {3, 6, 9};System.out.println(letters.length);

Array length: practice

• Use your alphabet array• Print array length

Array iteration: example

• String[] names = {"Nescafe", "Jacobs", "Maccofe"};

• for (String name : names) {• System.out.println(name);• }

Array iteration: practice

• Use months array• Print all months

Disadvantages of array

• You set size when you declare. Then you can not change its size

• You can use only same data type

What is ArrayList?

• An ArrayList is a dynamic data structure, meaning items can be added and removed from the list.

When to use ArrayList?

• When you are not sure about size• When your data collection is dynamic

Integer ArrayList: example

ArrayList<Integer> numbers = new ArrayList<Integer>();numbers.add(1);numbers.add(2);numbers.add(3);System.out.println(numbers.get(0));

Integer ArrayList: practice

• Create int ArrayList: numbers• Add numbers from 1 to 10• Print 5th number

String ArrayList: example

ArrayList<String> weekdays = new ArrayList<String>();weekdays.add("Monday");weekdays.add("Tuesday");weekdays.add("Wednesday");System.out.println(weekdays.get(1));

String ArrayList: practice

• Create String ArrayList: months• Print June using ArrayList

Boolean ArrayList: example

ArrayList<Boolean> isOrel = new ArrayList<Boolean>();isOrel.add(true);isOrel.add(false);isOrel.add(false);System.out.println(isOrel.get(0));

Boolean ArrayList: practice

• Create Boolean ArrayList: isReshka• Size: 5• Add boolean values• Print 3rd value

Character ArrayList: example

ArrayList<Character> letters = new ArrayList<Character>();letters.add('a');letters.add('b');letters.add('c');System.out.println(letters.get(2));

Character ArrayList: practice

• Create Character ArrayList: alphabet• Add all letters to ArrayList• Print 10th letter• Print 20th letter

ArrayList remove: example

ArrayList<String> names = new ArrayList<String>();names.add("Vadim");names.add("Jonik");names.add("Timur");names.remove(1);System.out.println(names);

ArrayList remove: practice

• Use String ArrayList: months• Remove 5th item• Print ArrayList

ArrayList size: example

ArrayList<String> names = new ArrayList<String>();names.add("Vadim");names.add("Jonik");names.add("Timur");System.out.println(names.size());

ArrayList size: practice

• Use previous String ArrayList: months• Print size of months ArrayList

ArrayList iteration: example

• Use months ArrayList• Print all months

HashMap

• Unordered list• Based on key-value

HashMap: example

HashMap<String, String> countryCodes = new HashMap<String, String>();countryCodes.put("UZ", "Uzbekistan");countryCodes.put("JP", "Japan");countryCodes.put("US", "United States");System.out.println(countryCodes.get("UZ"));

HashMap: practice

• Create HashMap: elements• Key: String• Value: String• Add values:• H – Hydron• O – Oxygen• N – Nitrogen• Print Oxygen

HashMap: practice 2

• Create Hashmap: httpCodes• Key: int• Value: String• 404 – Not found• 403 – Forbidden• 400 – Bad request• Print “Not found”

HashMap: practice 3

• Create HashMap: capitals• Key: String• Value: String• Uzbekistan – Tashkent• Japan – Tokyo• US – Washington• Print Japan’s capital city

Questions?

• Any questions?

Review

• Lynda.com - 8. Using Data Collections

Thank you!

• Thank you very much for your attention!