Date post: | 02-Jan-2016 |
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When to use array?
• When you know exact number of data in list
• When all data in the same data type
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]);
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 iteration: example
• String[] names = {"Nescafe", "Jacobs", "Maccofe"};
• for (String name : names) {• System.out.println(name);• }
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.
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));
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 size: example
ArrayList<String> names = new ArrayList<String>();names.add("Vadim");names.add("Jonik");names.add("Timur");System.out.println(names.size());
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