Example of Inheritance and use of JTextArea

import java.io.*;import javax.swing.*;import java.awt.event.*;import java.awt.*;public class important{public static void main(String args[]){JTextArea outarea= new JTextArea(400,50);Human person = new Human();Student learner = new Student();person.setName(“Zeynep Altan");person.setAge(23);learner.setName(“Özlem Yıldız");String nn=learner.getName(); // in other words: inheritanceJOptionPane.showMessageDialog(null," "+nn);learner.setRank();String out="name " +person.getName()+“ "+learner.getRank();outarea.setText(out);JOptionPane.showMessageDialog(null,outarea);System.exit(0);} }

public class Human{private String name= new String();private int age;public Human(){name=" ";age=0;}public void setName(String st)//Sets the index name. Explicit setting of an index name is not required {name=st;}public void setAge(int ag){age=ag;}public String getName(){//Returns the index name. Explicit setting of an index name is not required.

return (name);} } 

import java.io.*;import javax.swing.*;import java.awt.event.*;import java.awt.*;public class Student extends Human{private int total_hours;private char rank;public Student(){total_hours=0;rank=' ';}public void setRank(){String rr=JOptionPane.showInputDialog("enter code 1 2 3 4 ");rank=rr.charAt(0) ;}public char getRank(){return (rank);} }

Packages & Interfaces

Packages are containers for classes that are used to keep the class name space dividedPackages are stored in a hierarchical manner

and are explicitly imported into new class definition.

A package allows us to create a class named List, which we can store it in our own package without concern that it will conflict with some other named List stored anywhere

Access Protection Classes and packages are both means of

encapsulating and containing the name space and scope of variables and methods.

Packages act as containers for classes and other subordinate packages

Classes act as containers for data and code. The class is Java’s smallest unit of abstraction.

Because of interaction between classes and packages, Java addresses four categories of visibility for class members

Access rights for the different elements class\ have access to private default protected public

elements elements elements elements

(no modifier)

own class (Base) yes yes yes yes

subclass –

same package(SubA) no yes yes yes

class – same

package (AnotherA) no yes yes yes

subclass - another

package (SubB) no no yes/no * yes

class – another

package (AnotherB) no no no yes

*Class SubB has access only to the inherited from Base protected elements, i.e. its own elements, but the protected data of other Base instances is not accessible from SubB.

package packageA; public class Base { public String publicStr = "publicString";protected String protectedStr = "protectedString"; String defaultStr = "defaultString"; private String privateStr = "privateString"; public void print() { System.out.println ("packageA.Base has access to"); System.out.println(" " + publicStr); System.out.println(" " + protectedStr); System.out.println(" " + defaultStr); System.out.println(" " + privateStr); Base b = new Base(); // other Base instance System.out.println(" b." + b.publicStr); System.out.println(" b." + b.protectedStr); System.out.println(" b." + b.defaultStr); System.out.println(" b." + b.privateStr); } }

package packageA; public class SubA extends Base { public void print() { System.out.println("packageA.SubA has access to");System.out.println(" " + publicStr + " (inherited from Base)"); System.out.println(" " + protectedStr + " (inherited from Base)"); System.out.println(" " + defaultStr + " (inherited from Base)"); // not accessible - private elements are even not inherited // System.out.println (privateStr); Base b = new Base(); // other Base instance

System.out.println(" b." + b.publicStr); System.out.println(" b." + b.protectedStr); System.out.println(" b." + b.defaultStr); // not accessible System.out.println (b.privateStr); } }

package packageA;

public class AnotherA {

public void print() { System.out.println ( packageA.AnotherA has access to");

Base b = new Base();

System.out.println (" b." + b.publicStr); System.out.println (" b." + b.protectedStr); System.out.println (" b." + b.defaultStr);

// not accessible System.out.println (b.privateStr);

}

}

package packageB; import packageA.Base; public class SubB extends Base { public void print() { System.out.println ("packageB.SubB has access to");System.out.println(" " + publicStr + " (inherited from Base)");// protectedStr is inherited element -> accessibleSystem.out.println(" " + protectedStr + " (inherited from Base)");// not accessible System.out.println(defaultStr); // not accessible System.out.println (privateStr); Base b = new Base(); //other Base instance

System.out.println(" b." + b.publicStr); // protected element, which belongs to other object -> not accessible

// System.out.println(b.protectedStr); // not accessible System.out.println (b.defaultStr); // not accessible System.out.println(b.privateStr); } }

package packageB;

import packageA.Base;

public class AnotherB {

public void print() {System.out.println("packageB.AnotherB has access to");

Base b = new Base();

System.out.println(" b." + b.publicStr);

// not accessible System.out.println(b.protectedStr);

// not accessible System.out.println(b.defaultStr);

// not accessible System.out.println(b.privateStr);

}

}

import packageA.*; import packageB.*; // testing class public class TestProtection { public static void main(String[] args) { // all classes are public, so class TestProtection // has access to all of them new Base().print(); new SubA().print(); new AnotherA().print(); new SubB().print(); new AnotherB().print(); } }

Summary

private is the most restrictive access level a private member is accessible only in the

class in which it is defined private members are not inherited by the

subclasses

Interfaces

The use of the interface keyword allows us to fully abstract the interface from its implementation

Using interface we can specify a set of methods which can be implemented by one or more classes.

The interface, itself does not define any implementation Although interfaces are similar to abstract classes, they

have an additional capability A class can implement more than one interface. Bu constract, a class can only inherit a single superclass

(abstract or otherwise)

Creating an Interfacemodifier interface InterfaceName{ constants declarations; methods signatures;}

Example of Creating an Interface//This interface is defined in java.lang//package

public interface Comparable{ public int compareTo(Object o);}

Generic max Method

public class Max{ // Return the maximum between two objects public static Comparable max (Comparable o1, Comparable o2) { if (o1.compareTo(o2) > 0) return o1; else return o2; }

}

The abstract Class

• The abstract class– Cannot be instantiated

– Should be extended and implemented in subclasses

• The abstract method– Method signature without

implementation

Comparator Interface

Is it possible to iterate over a set of Person objects in age order?

Is it possible to construct a TreeSet of objects that do not implement Comparable?

Answer: Yes, we can use an object that implements Comparator

The Comparator interface has a single method, similar to Comparable:

int compare(Object a, Object b)

Like Comparable.compareTo() it returns an integer, whose sign encodes the comparison

JPanel Basics In the simplest case, we use a JPanel exactly the same way as

a Panel. JPanel also acts as a replacement for Canvas (there is no

JCanvas). When using JPanel we should firstly set the preferred size via

setPreferredSize (recall that a Canvas' preferred size is just its current size, while a Panel and JPanel determine their preferred size from the components they contain).

Secondly, we should use paintComponent for drawing, not paint.

Since double-buffering is turned on by default, the first thing we normally do in paintComponent is clear the off-screen bitmap via super.paintComponent.

public void paintComponent(Graphics g) { super.paintComponent(g); ... } existing Border objects whenever possible.

Beside from double buffering, the most obvious new feature is the ability to assign borders to JPanels.

Swing gives us seven basic border types: titled, etched, beveled (regular plus a "softer" version), line, matte, compound, and empty.

we can also create our own. We can assign a Border via the setBorder method, and

create the Border either by calling the constructors directly, or more often by using one of the following convenience methods in BorderFactory:

createTitledBorder, createEtchedBorder, createBevelBorder, createRaisedBevelBorder, createLoweredBevelBorder, createLineBorder, createMatteBorder, createCompoundBorder, createEmptyBorder.

These factory methods reuse existing Border objects whenever possible.

import java.awt.*;import javax.swing.*;// This example illustrates the use of JPanels, the ability to add Borders public class JPanels extends JFrame { public static void main(String[] args) { new JPanels(); }

public JPanels() { super ("Using JPanels with Borders");

WindowUtilities.setNativeLookAndFeel(); addWindowListener(new ExitListener()); Container content = getContentPane(); content.setBackground(Color.lightGray); JPanel controlArea = new JPanel (new GridLayout(3, 1)); String[] colors = { "Red", "Green", "Blue", "Black", "White", "Gray" }; controlArea.add (new SixChoicePanel ("Color", colors)); String[] thicknesses = { "1", "2", "3", "4", "5", "6" };

controlArea.add (new SixChoicePanel("Line Thickness", thicknesses));

String[] fontSizes = { "10", "12", "14", "18", "24", "36" };

controlArea.add(new SixChoicePanel("Font Size", fontSizes));

content.add(controlArea, BorderLayout.EAST););

} }

JPanel drawingArea = new JPanel();

// Preferred height is irrelevant, since using WEST region

drawingArea.setPreferredSize(new Dimension(400, 0));drawingArea.setBorder(BorderFactory.createLineBorder (Color.blue, 2));

drawingArea.setBackground(Color.white);

content.add(drawingArea, BorderLayout.WEST);

pack();

setVisible(true); }

import java.awt.*; import javax.swing.*; public class SixChoicePanel extends JPanel { public SixChoicePanel(String title, String[] buttonLabels) { super (new GridLayout(3, 2)); setBackground (Color.lightGray);setBorder(BorderFactory.createTitledBorder(title)); ButtonGroup group = new ButtonGroup(); JRadioButton option; int halfLength = buttonLabels.length/2; // Assumes even length for (int i=0; i<halfLength; i++) { option = new JRadioButton(buttonLabels[i]); group.add(option); add(option); option = new JRadioButton (buttonLabels[i+halfLength]);

group.add(option); add(option); } }

WindowsUtilities.javaimport javax.swing.*;import java.awt.*;

public class WindowUtilities {

public static void setNativeLookAndFeel() { try {UIManager.setLookAndFeel(UIManager.getSystemLook AndFeelClassName()); } catch(Exception e) { System.out.println("Error setting native LAF: " + e); } }

public static void setJavaLookAndFeel() { try { UIManager.setLookAndFeel (UIManager.getCrossPlatformLookAndFeelClassName()); } catch(Exception e) { System.out.println("Error setting Java LAF: " + e); } }

public static void setMotifLookAndFeel() { try { UIManager.setLookAndFeel ("com.sun.java.swing.plaf.motif.MotifLookAndFeel"); } catch(Exception e) { System.out.println("Error setting Motif LAF: " + e); } }

public static JFrame openInJFrame(Container content, int width, int height, String title, Color bgColor) { JFrame frame = new JFrame(title); frame.setBackground(bgColor); content.setBackground(bgColor); frame.setSize(width, height); frame.setContentPane(content); frame.addWindowListener(new ExitListener()); frame.setVisible(true); return(frame); } //Uses Color.white as the background color. public static JFrame openInJFrame(Container content int width, int height, String title) { return(openInJFrame (content, width, height, title, Color.white)); } //Uses Color.white as the background color, and the name of the Container's // class as the JFrame title. public static JFrame openInJFrame(Container content, int width, int height) { return(openInJFrame(content, width, height, content.getClass().getName(), Color.white)); } }