The document discusses various Java collection classes including LinkedList, ArrayList, Sets, Maps, and inner classes. It provides examples of how to use HashSet, HashMap, and inner classes. It notes that LinkedList was designed to make add/remove faster than ArrayList. It also summarizes that Sets cannot contain duplicate elements unlike Lists, and Maps store objects in key-value pairs. Finally, it demonstrates using an inner class as an event listener and the advantages of inner classes for code cohesion and convenience.

1. Lecture 8
More on collections
Object Oriented Programming
Eastern University, Dhaka
Md. Raihan Kibria

2. LinkedList
 LinkedList is just like ArrayList; however, it
was designed to make add/remove faster
and efficient
 Has these methods:
 addFirst
 AddLast
 removeFirst
 removeLast

3. Who implements List interface
 ArrayList
 LinkedList
 Vector
 Stack

4. 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

5. Output
size of set: 4
0
1
2
3
size of list: 5
0
1
2
3
3
We can see set did not add duplicate element

6. 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

7. 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

8. HashMap example
public 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:
31
null

9. Inner classes
Next slide: a demo without using inner class

10. 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{
@Override
public void actionPerformed(ActionEvent arg0) {
JOptionPane.showMessageDialog(null,
"Eggs are not supposed to be green.");
}
}

11. After Run the Program
After Clicking the Test Button

12. 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());
}
}

13. After Run the Program
After Clicking the Test Button for
Once

14. After Clicking the Test Button for
Twice
After Clicking the Test Button for
Thrice

15. Advantages of using Inner class
Improves code-cohesion
Provides convenience to the developer