Inner Classes in Java Example Program

Java Inner Class Example Codes

import java.awt.*;

import java.awt.event.*;

import java.util.*;

import javax.swing.*;

import javax.swing.Timer;

/**

* This program demonstrates the use of inner classes.

*/

public class InnerClassTest

{

public static void main(String[] args)

{

TalkingClock clock = new TalkingClock(1000, true);

clock.start();

// keep program running until user selects "Ok"

JOptionPane.showMessageDialog(null, "Quit program?");

System.exit(0);

}

}

/**

* A clock that prints the time in regular intervals.

*/

class TalkingClock

{

/**

* Constructs a talking clock

* @param interval the interval between messages (in milliseconds)

* @param beep true if the clock should beep

*/

public TalkingClock(int interval, boolean beep)

{

this.interval = interval;

this.beep = beep;

}

/**

* Starts the clock.

*/

public void start()

{

ActionListener listener = new TimePrinter();

Timer t = new Timer(interval, listener);

t.start();

}

private int interval;

private boolean beep;

public class TimePrinter implements ActionListener

{

public void actionPerformed(ActionEvent event)

{

Date now = new Date();

System.out.println("At the tone, the time is " + now);

if (beep) Toolkit.getDefaultToolkit().beep();

}

}

}

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Sample Java Codes for Interface

Comparable interface Java Example Codes

import java.util.*;

/**

* This program demonstrates the use of the Comparable interface.

*/

public class EmployeeSortTest

{

public static void main(String[] args)

{

Employee[] staff = new Employee[3];

staff[0] = new Employee("Harry Hacker", 35000);

staff[1] = new Employee("Carl Cracker", 75000);

staff[2] = new Employee("Tony Tester", 38000);

Arrays.sort(staff);

// print out information about all Employee objects

for (Employee e : staff)

System.out.println("name=" + e.getName() + ",salary=" + e.getSalary());

}

}

class Employee implements Comparable

{

public Employee(String n, double s)

{

name = n;

salary = s;

}

public String getName()

{

return name;

}

public double getSalary()

{

return salary;

}

public void raiseSalary(double byPercent)

{

double raise = salary * byPercent / 100;

salary += raise;

}

/**

* Compares employees by salary

* @param other another Employee object

* @return a negative value if this employee has a lower salary than

* otherObject, 0 if the salaries are the same, a positive value otherwise

*/

public int compareTo(Employee other)

{

if (salary <>

if (salary > other.salary) return 1;

return 0;

}

private String name;

private double salary;

}

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Java Clone sample Codes

Cloning in Java

import java.util.*;

/**

* This program demonstrates cloning.

*/

public class CloneTest

{

public static void main(String[] args)

{

try

{

Employee original = new Employee("John Q. Public", 50000);

original.setHireDay(2000, 1, 1);

Employee copy = original.clone();

copy.raiseSalary(10);

copy.setHireDay(2002, 12, 31);

System.out.println("original=" + original);

System.out.println("copy=" + copy);

}

catch (CloneNotSupportedException e)

{

e.printStackTrace();

}

}

}

class Employee implements Cloneable

{

public Employee(String n, double s)

{

name = n;

salary = s;

hireDay = new Date();

}

public Employee clone() throws CloneNotSupportedException

{

// call Object.clone()

Employee cloned = (Employee) super.clone();

// clone mutable fields

cloned.hireDay = (Date) hireDay.clone();

return cloned;

}

/**

* Set the hire day to a given date.

* @param year the year of the hire day

* @param month the month of the hire day

* @param day the day of the hire day

*/

public void setHireDay(int year, int month, int day)

{

Date newHireDay = new GregorianCalendar(year, month - 1, day).getTime();

// Example of instance field mutation

hireDay.setTime(newHireDay.getTime());

}

public void raiseSalary(double byPercent)

{

double raise = salary * byPercent / 100;

salary += raise;

}

public String toString()

{

return "Employee[name=" + name + ",salary=" + salary + ",hireDay=" + hireDay + "]";

}

private String name;

private double salary;

private Date hireDay;

}

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Anonymous Inner Classes Program in Java

Anonymous Inner Classes

import java.awt.*;

import java.awt.event.*;

import java.util.*;

import javax.swing.*;

import javax.swing.Timer;

/**

* This program demonstrates anonymous inner classes.

*/

public class AnonymousInnerClassTest

{

public static void main(String[] args)

{

TalkingClock clock = new TalkingClock();

clock.start(1000, true);

// keep program running until user selects "Ok"

JOptionPane.showMessageDialog(null, "Quit program?");

System.exit(0);

}

}

/**

* A clock that prints the time in regular intervals.

*/

class TalkingClock

{

/**

* Starts the clock.

* @param interval the interval between messages (in milliseconds)

* @param beep true if the clock should beep

*/

public void start(int interval, final boolean beep)

{

ActionListener listener = new ActionListener()

{

public void actionPerformed(ActionEvent event)

{

Date now = new Date();

System.out.println("At the tone, the time is " + now);

if (beep) Toolkit.getDefaultToolkit().beep();

}

};

Timer t = new Timer(interval, listener);

t.start();

}

}

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Java Classes Features by Reflection

Features of Java Classes

import java.util.*;

import java.lang.reflect.*;

/**

* This program uses reflection to print all features of a class.

*/

public class ReflectionTest

{

public static void main(String[] args)

{

// read class name from command line args or user input

String name;

if (args.length > 0) name = args[0];

else

{

Scanner in = new Scanner(System.in);

System.out.println("Enter class name (e.g. java.util.Date): ");

name = in.next();

}

try

{

// print class name and superclass name (if != Object)

Class cl = Class.forName(name);

Class supercl = cl.getSuperclass();

String modifiers = Modifier.toString(cl.getModifiers());

if (modifiers.length() > 0) System.out.print(modifiers + " ");

System.out.print("class " + name);

if (supercl != null && supercl != Object.class) System.out.print(" extends "

+ supercl.getName());

System.out.print("\n{\n");

printConstructors(cl);

System.out.println();

printMethods(cl);

System.out.println();

printFields(cl);

System.out.println("}");

}

catch (ClassNotFoundException e)

{

e.printStackTrace();

}

System.exit(0);

}

/**

* Prints all constructors of a class

* @param cl a class

*/

public static void printConstructors(Class cl)

{

Constructor[] constructors = cl.getDeclaredConstructors();

for (Constructor c : constructors)

{

String name = c.getName();

System.out.print(" ");

String modifiers = Modifier.toString(c.getModifiers());

if (modifiers.length() > 0) System.out.print(modifiers + " ");

System.out.print(name + "(");

// print parameter types

Class[] paramTypes = c.getParameterTypes();

for (int j = 0; j <>

{

if (j > 0) System.out.print(", ");

System.out.print(paramTypes[j].getName());

}

System.out.println(");");

}

}

/**

* Prints all methods of a class

* @param cl a class

*/

public static void printMethods(Class cl)

{

Method[] methods = cl.getDeclaredMethods();

for (Method m : methods)

{

Class retType = m.getReturnType();

String name = m.getName();

System.out.print(" ");

// print modifiers, return type and method name

String modifiers = Modifier.toString(m.getModifiers());

if (modifiers.length() > 0) System.out.print(modifiers + " ");

System.out.print(retType.getName() + " " + name + "(");

// print parameter types

Class[] paramTypes = m.getParameterTypes();

for (int j = 0; j <>

{

if (j > 0) System.out.print(", ");

System.out.print(paramTypes[j].getName());

}

System.out.println(");");

}

}

/**

* Prints all fields of a class

* @param cl a class

*/

public static void printFields(Class cl)

{

Field[] fields = cl.getDeclaredFields();

for (Field f : fields)

{

Class type = f.getType();

String name = f.getName();

System.out.print(" ");

String modifiers = Modifier.toString(f.getModifiers());

if (modifiers.length() > 0) System.out.print(modifiers + " ");

System.out.println(type.getName() + " " + name + ";");

}

}

}

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Example Programs for Java Abstract Classes

Abstract Classes in Java

import java.util.*;

/**

* This program demonstrates abstract classes.

*/

public class PersonTest

{

public static void main(String[] args)

{

Person[] people = new Person[2];

// fill the people array with Student and Employee objects

people[0] = new Employee("Harry Hacker", 50000, 1989, 10, 1);

people[1] = new Student("Maria Morris", "computer science");

// print out names and descriptions of all Person objects

for (Person p : people)

System.out.println(p.getName() + ", " + p.getDescription());

}

}

abstract class Person

{

public Person(String n)

{

name = n;

}

public abstract String getDescription();

public String getName()

{

return name;

}

private String name;

}

class Employee extends Person

{

public Employee(String n, double s, int year, int month, int day)

{

super(n);

salary = s;

GregorianCalendar calendar = new GregorianCalendar(year, month - 1, day);

hireDay = calendar.getTime();

}

public double getSalary()

{

return salary;

}

public Date getHireDay()

{

return hireDay;

}

public String getDescription()

{

return String.format("an employee with a salary of $%.2f", salary);

}

public void raiseSalary(double byPercent)

{

double raise = salary * byPercent / 100;

salary += raise;

}

private double salary;

private Date hireDay;

}

class Student extends Person

{

/**

* @param n the student's name

* @param m the student's major

*/

public Student(String n, String m)

{

// pass n to superclass constructor

super(n);

major = m;

}

public String getDescription()

{

return "a student majoring in " + major;

}

private String major;

}

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Java Source code for Reflection to Spy on Objects

Reflection to Spy on Objects

import java.lang.reflect.*;

import java.util.*;

/**

* This program uses reflection to spy on objects.

*/

public class ObjectAnalyzerTest

{

public static void main(String[] args)

{

ArrayList squares = new ArrayList();

for (int i = 1; i <= 5; i++)

squares.add(i * i);

System.out.println(new ObjectAnalyzer().toString(squares));

}

}

class ObjectAnalyzer

{

/**

* Converts an object to a string representation that lists all fields.

* @param obj an object

* @return a string with the object's class name and all field names and

* values

*/

public String toString(Object obj)

{

if (obj == null) return "null";

if (visited.contains(obj)) return "...";

visited.add(obj);

Class cl = obj.getClass();

if (cl == String.class) return (String) obj;

if (cl.isArray())

{

String r = cl.getComponentType() + "[]{";

for (int i = 0; i <>

{

if (i > 0) r += ",";

Object val = Array.get(obj, i);

if (cl.getComponentType().isPrimitive()) r += val;

else r += toString(val);

}

return r + "}";

}

String r = cl.getName();

// inspect the fields of this class and all superclasses

do

{

r += "[";

Field[] fields = cl.getDeclaredFields();

AccessibleObject.setAccessible(fields, true);

// get the names and values of all fields

for (Field f : fields)

{

if (!Modifier.isStatic(f.getModifiers()))

{

if (!r.endsWith("[")) r += ",";

r += f.getName() + "=";

try

{

Class t = f.getType();

Object val = f.get(obj);

if (t.isPrimitive()) r += val;

else r += toString(val);

}

catch (Exception e)

{

e.printStackTrace();

}

}

}

r += "]";

cl = cl.getSuperclass();

}

while (cl != null);

return r;

}

private ArrayList

}

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