More on collections

Lecture 8

Object Oriented ProgrammingEastern University, Dhaka

Md. Raihan Kibria

LinkedList

LinkedList is just like ArrayList; however, it was designed to make add/remove faster and efficient

Has these methods: addFirst AddLast removeFirst removeLast

Who implements List interface

ArrayList LinkedList Vector Stack

Sets

Examples are HashSet, TreeSet

Difference between Set and List A list can have duplicate objects Set cannot have duplicate objects See example in the next slide

Output

size of set: 40123size of list: 501233

We can see set did not add duplicate element

public class SetDemo {

public static void main(String[] args) { Set<Integer>set = new HashSet<Integer>(); List<Integer>list = new ArrayList<Integer>();

for (int i=0; i<4; i++){ set.add(new Integer(i)); list.add(new Integer(i)); }

set.add(3); list.add(3);

System.out.println("size of set: " + set.size()); for (int i=0; i<set.size(); i++) System.out.println(set.toArray()[i]);

System.out.println("size of list: " + list.size()); for (int i=0; i<list.size(); i++) System.out.println(list.get(i)); }}

Output in the following slide

Map interface

Object to a map are key,value pairs For example, <dhaka, 02><chittagong, 031><sylhet, 032> Two most common map implementations

are HashMap and TreeMap

HashMap examplepublic class MapDemo { public static void main(String[] args) { Map<String, Integer>map = new HashMap<String, Integer>(); map.put("Dhaka", 2); map.put("Chittagong", 31); map.put("Sylhet", 32);

System.out.println(map.get("Chittagong")); System.out.println(map.get("Comilla")); }}

Output is:31null

Inner classes

Next slide: a demo without using inner class

public class ButtonListenerDemo {

public static void main(String[] args) { JFrame jframe = new JFrame(); jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); jframe.setBounds(0, 0, 300, 200); jframe.setLayout(new FlowLayout());

JButton jbutton = new JButton("Test button"); jframe.add(jbutton); jbutton.addActionListener(new ButtonListener());

JTextField jtext = new JTextField(); jframe.getContentPane().add(jtext); jtext.setText("Hello"); jframe.setVisible(true); }}

class ButtonListener implements ActionListener{

@Overridepublic void actionPerformed(ActionEvent arg0) { JOptionPane.showMessageDialog(null, "Eggs are not supposed to be green."); }}

After Run the Program

After Clicking the Test Button

public class ButtonListenerDemo2 {

public static void main(String[] args) { JFrame jframe = new JFrame(); jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); jframe.setBounds(0, 0, 300, 200); jframe.setLayout(new FlowLayout());

final JTextField jtext = new JTextField(); jframe.getContentPane().add(jtext); jtext.setText("Hello"); jframe.setVisible(true);

final int i=0; class MyButtonListener implements ActionListener{

int j = i; @Override public void actionPerformed(ActionEvent arg0) { jtext.setText(String.valueOf(j++)); } }

JButton jbutton = new JButton("Test button"); jframe.add(jbutton); jbutton.addActionListener(new MyButtonListener()); }}

After Run the Program

After Clicking the Test Button for Once

After Clicking the Test Button for Twice

After Clicking the Test Button for Thrice

Advantages of using Inner class

Improves code-cohesionProvides convenience to the developer