Object-Oriend Programming using Java

1. CS3135/CS2135
Object Oriented Programming (Java)
BSCS-3 / MCS-3
Lecture # 5
Inheritance
Dialog boxes
Parsing

2. INHERITANCE
• Inheritance is the reusability of predefined functionality.
• Existing class is called superclass (base class in C++)and new class is called subclass (derived class in C++).
• Inheritance is also called Specialization because subclass can modify the behavior of its superclass
appropriately to that subclass.
• Direct superclass is the superclass from which subclass explicitly inherits.
• Indirect superclass is any class above the direct superclass in class hierarchy.
• In Java, class hierarchy begins with class Object (in package java.lang), which every class in Java directly or
indirectly extends.
• Java supports only single inheritance, in which each class is derived from exactly one direct superclass. It
does not support multiple inheritance.
Instructor: Tanzila Kehkashan
2

3. INHERITANCE
A superclass’s
• Public members are accessible wherever the program has
reference to an object of that superclass or one of its superclass.
• Private members can be accessed directly only within the
superclass’s declaration.
• Protected members have an inheritance level of protection
between public and private access. They can be accessed by
members of superclass and subclass and other classes in same
package.
• A superclass’s private methods are hidden in its subclass and can
be accessed only through the public or protected methods inherited
from the superclass.
Relationship between superclass & subclass
• A subclass can invoke a constructor of its superclass by using the
keyword super followed by a set of parentheses containing the
superclass constructor arguments. This must appear as the first
statement in the subclass’s constructor body.
Example
public class person
{
}
public class student extends person
{
}
public class employee extends person
{
}
public class result extends student
{
}
Instructor: Tanzila Kehkashan
3

4. GUI Components
• GUI component is an object with which the user interacts via mouse, keyboard or
another form of input, such as voice recognition.
• These are sometimes called controls or widgets (window gadgets).
• Lightweight Vs. Heavyweight GUI components
• Swing Vs. AWT components
• There are two sets of Java GUI components:
• ‘java.awt’ package (Abstract Window Toolkit)
• ‘javax.swing’ package
Instructor: Tanzila Kehkashan
4

5. GUI Components -> Dialogue Boxes
• Simple GUI based I/O with JOptionPane
• import javax.swing.JOptionPane;
• Message dialog
• Input dialog
• Option dialog
• Confirm dialog
• Dialog Constants / message Type
• ERROR_MESSAGE
• INFORMATION_MESSAGE
• WARNING_MESSAGE
• QUESTION_MESSAGE
• PLAIN_MESSAGE
Instructor: Tanzila Kehkashan
5

6. JOptionPane Methods
• static void showMessageDialog(Component, Object)
• static void showMessageDialog(Component, Object, String, int)
• static void showMessageDialog(Component, Object, String, int, Icon)
• static int showOptionDialog(Component, Object, String, int, int, Icon, Object[], Object)
• static int showConfirmDialog(Component, Object)
• static int showConfirmDialog(Component, Object, String, int)
• static int showConfirmDialog(Component, Object, String, int, int)
• static int showConfirmDialog(Component, Object, String, int, int, Icon)
• static String showInputDialog(Object)
• static String showInputDialog(Component, Object)
• static String showInputDialog(Component, Object, String, int)
• static String showInputDialog(Component, Object, String, int, Icon, Object[], Object)
Instructor: Tanzila Kehkashan
6

7. GUI Components -> Option Type
• DEFAULT_OPTION
• YES_NO_OPTION
• YES_NO_CANCEL_OPTION
• OK_CANCEL_OPTION
Return Values
• YES_OPTION
• NO_OPTION
• CANCEL_OPTION
• OK_OPTION
• CLOSED_OPTION
GUI Components -> Dialogue Box Constants
Instructor: Tanzila Kehkashan
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8. Parse methods convert strings to numeric data types. These are
• Byte.parseByte(String)
• Integer.parseInt(String)
• Short.parseShort(String)
• Long.parseLong(String)
• Float.parseFloat(String)
• Double.parseDouble(String)
String Parse
Instructor: Tanzila Kehkashan
8

9. Instructor: Tanzila Kehkashan
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10. Instructor: Tanzila Kehkashan
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11. Instructor: Tanzila Kehkashan
11