Why is Boolean class is Comparable
Why is Boolean class made to be Comparable from Java 5?
Boolean represents true and false conditions, and there is no
question of comparing boolean values in terms of greater or less.
Then what was the need to make Boolean class comparable,
whereas the comparision of boolean type is not valid.
Thanks
Pravin
PMJain wrote:
Yes not everything is supposed to be Comparable, is different from saying that everything should not be Comparable. Your logic is "Boolean should not be comparable because you cannot use <, >, etc." By that logic String should not be comparable.
Do not force Comparable unnecessarily on everything.Where the hell did you get the ridiculous idea that I was? I pointed out a case where Boolean being comparable is useful. That's a far cry from "forcing comparable unnecessarily on everything."
Whatever has natural ordering only should be Comparable, and for other unnatural orderings we have the Comparator.You really don't realize how illogical that is? Okay, well, like I said, you're entitled to your opinion, and you're entitled to never use Boolean as a Comparable, and instead create a Comparator. Fortunately for me, however, it is Comparable, so I can use it that way when it's appropriate.
Similar Messages
-
Ok Why Does Boolean NOT implement Comparable
Ok.. im looking for a logical reason to why Boolean does NOT implement Comparable?
Every other wrapper does. ( Integer, Double ect.. ) Just not Boolean..
anyone got any logical guesses as to Why?
( just for context here is how i came upon this.. )
I have a quicksort algorythm that reads in an arraylist and does some manipulation of it. All that is demands is that the objects in the list be comparable. This algorythm has worked beautifully (and fast) for serveral months.. till someone put a Boolean in the list.. doh!
Thanks,
JMGUsing the collections.sort() would mean that each object would have to implement comparable anyways. It also means that these objects would only be sortable by one set of tests. I wish to sort my objects by any of their properties. Hence now my properties must implement comparable. ( given that this app usings mostly int, double and String its not a big deal) What surprised me was the Double did not implement comparable where all other wrappers did.. thats it..
mostly i was just currious as to if there was a larger reason to why it was not implemented other than we just could not decided which should be valued higher :)
JMG -
Sorting a vector of objects using attribute of object class as comparator
i would like to sort a vector of objects using an attribute of object class as comparator. let me explain, i'm not sure to be clear.
class MyObject{
String name;
int value1;
int value2;
int value3;
i've got a Vector made of MyObject objects, and i would sort it, for instance, into ascending numerical order of the value1 attribute. Could someone help me please?
KINSKI.Vector does not implement a sorted collection, so you can't use a Comparator. Why don't you use a TreeSet? Then you couldclass MyObject
String name;
int value1;
int value2;
int value3;
// Override equals() in this class to match what our comparator does
boolean equals (Object cand)
// Verify comparability; this will also allow subclasses.
if (cand !instanceof MyObject)
throw new ClassCastException();
return value1 = cand.value1;
// Provide the comparator for this class. Make it static; instance not required
static Comparator getComparator ()
// Return this class's comparator
return new MyClassComparator();
// Define a comparator for this class
private static class MyClassComparator implements Comparator
compare (Object cand1, Object cand2)
// Verify comparability; this will also allow subclasses.
if ((cand1 !instanceof MyObject) || (cand2 !instanceof MyObject))
throw new ClassCastException();
// Compare. Less-than return -1
if ((MyObject) cand1.value1 < (MyObject) cand2.value1))
return -1;
// Greater-than return 1
else if ((MyObject) cand1.value1 > (MyObject) cand2.value1))
return 1;
// Equal-to return 0.
else
return 0;
}then just pass MyObject.getComparator() (you don't need to create an instance) when you create the TreeSet. -
Why can't classes with private constructors be subclassed?
Why can't classes with private constructors be subclassed?
I know specifying a private nullary constructor means you dont want the class to be instantiated or the class is a factory or a singleton pattern. I know the workaround is to just wrap all the methods of the intended superclass, but that just seems less wizardly.
Example:
I really, really want to be able to subclass java.util.Arrays, like so:
package com.tassajara.util;
import java.util.LinkedList;
import java.util.List;
public class Arrays extends java.util.Arrays {
public static List asList(boolean[] array) {
List result = new LinkedList();
for (int i = 0; i < array.length; i++)
result.add(new Boolean(array));
return result;
public static List asList( char[] array) {
List result = new LinkedList();
for (int i = 0; i < array.length; i++)
result.add(new Character(array[i]));
return result;
public static List asList( byte[] array) {
List result = new LinkedList();
for (int i = 0; i < array.length; i++)
result.add(new Byte(array[i]));
return result;
public static List asList( short[] array) {
List result = new LinkedList();
for (int i = 0; i < array.length; i++)
result.add(new Short(array[i]));
return result;
public static List asList( int[] array) {
List result = new LinkedList();
for (int i = 0; i < array.length; i++)
result.add(new Integer(array[i]));
return result;
public static List asList( long[] array) {
List result = new LinkedList();
for (int i = 0; i < array.length; i++)
result.add(new Long(array[i]));
return result;
public static List asList( float[] array) {
List result = new LinkedList();
for (int i = 0; i < array.length; i++)
result.add(new Float(array[i]));
return result;
public static List asList( double[] array) {
List result = new LinkedList();
for (int i = 0; i < array.length; i++)
result.add(new Double(array[i]));
return result;
// Now that we extend java.util.Arrays this method is not needed.
// /**JCF already does this so just wrap their implementation
// public static List asList(Object[] array) {
// return java.util.Arrays.asList(array);
public static List asList(Object object) {
List result;
Class type = object.getClass().getComponentType();
if (type != null && type.isPrimitive()) {
if (type == Boolean.TYPE)
result = asList((boolean[])object);
else if (type == Character.TYPE)
result = asList(( char[])object);
else if (type == Byte.TYPE)
result = asList(( byte[])object);
else if (type == Short.TYPE)
result = asList(( short[])object);
else if (type == Integer.TYPE)
result = asList(( int[])object);
else if (type == Long.TYPE)
result = asList(( long[])object);
else if (type == Float.TYPE)
result = asList(( float[])object);
else if (type == Double.TYPE)
result = asList(( double[])object);
} else {
result = java.util.Arrays.asList((Object[])object);
return result;
I do not intend to instantiate com.tassajara.util.Arrays as all my methods are static just like java.util.Arrays. You can see where I started to wrap asList(Object[] o). I could continue and wrap all of java.util.Arrays methods, but thats annoying and much less elegant.Why can't classes with private constructors be
subclassed?Because the subclass can't access the superclass constructor.
I really, really want to be able to subclass
java.util.Arrays, like so:Why? It only contains static methods, so why don't you just create a separate class?
I do not intend to instantiate
com.tassajara.util.Arrays as all my methods are static
just like java.util.Arrays. You can see where I
started to wrap asList(Object[] o). I could continue
and wrap all of java.util.Arrays methods, but thats
annoying and much less elegant.There's no need to duplicate all the methods - just call them when you want to use them.
It really does sound like you're barking up the wrong tree here. I can see no good reason to want to subclass java.util.Arrays. Could you could explain why you want to do that? - perhaps you are misunderstanding static methods.
Precisely as you said, if they didn't want me to
subclass it they would have declared it final.Classes with no non-private constructors are implicitly final.
But they didn't. There has to be a way for an API
developer to indicate that a class is merely not to be
instantiated, and not both uninstantiable and
unextendable.There is - declare it abstract. Since that isn't what was done here, I would assume the writers don't want you to be able to subclass java.util.Arrays -
Why a base class cannot be a Private or Protected ?????
why a base class cannot be a Private or Protected ?????
why a base class cannot be a Private orProtected
?????Who would be able to access it? (Assuming "base"
means top-level class.)Private, none. Protected, all classes in same package
and subclasses (as with the methods).
Actually, its somewhat illogical that a class be
declared package-private, but not protected, since
protected is less restrictive.having a protected class would make no sense. subclasses are not permitted to lessen the protection of members of their superclass, so you'd end up with a class that nothing could use, except subclasses that in turn nothing else could use -
Why interfaces why not abstract classes?
why they are using interfaces concept in JDBC or struts2.0 why not abstract classes?
thanks in advance.user5287726 wrote:
jverd wrote:
user5287726 wrote:
Interfaces are more flexible. For certain definitions of flexible, yes, but not for others.
A Java class can only inherit one class, but it can implement multiple interfaces.Which has absolutely nothing to do with why JDBC declares interfaces rather than abstract classes.How does your post even attempt to answer the OP's question?OP asked: "why they are using interfaces concept in JDBC or struts2.0 why not abstract classes?" I'm pointing out that your post does not address the question asked. And of course your answer is wrong anyway.
As for addressing the OP's question, I did that in my first response. -
Why Array.as class is made dynamic?
Why Array.as class is made dynamic?
public dynamic class ArrayFor one thing, array "elements" are merely dynamic properties. For example, when you access a[0] you are really accessing a["0"], i.e., a dynamic property named "0".
For another thing, Ecmascript requires Array to allow accessing any property, such as a["foo"].
Gordon Smith, Adobe -
Why a static class can implements a non-static interface?
public class Test {
interface II {
public void foo();
static class Impl implements II {
public void foo() {
System.out.println("foo");
}Why a static class can implements a non-static interface?
In my mind, static members cann't "use" non-static members.Why a static class can implements a
non-static interface?There's no such thing as a non-static member interface. They are always static even if you don't declare them as such.
An interface defines, well, a public interface to be implemented. It doesn't matter whether it is implemented by a static nested class or by an inner class (or by any class at all). It wouldn't make sense to enforce that it should be one or the other, since the difference between a static and non-static class is surely an irrelevant detail to the client code of the interface.
In my mind, static members cann't "use" non-static
members.
http://java.sun.com/docs/books/jls/third_edition/html/classes.html#246026
Member interfaces are always implicitly static. It is permitted but not required for the declaration of a member interface to explicitly list the static modifier. -
I am confused about the purpose of helper classes when using EJB's. Is the idea simply to make the code more maintainable? To separate data access code from the business logic? To aid the reuse of code? Why should I choose to use a helper class rather than creating a new EJB to do the job?
I have been unable to find any comprehensive articles, and am a bit confused!
Thanks in advance.- split out code into distinct functional models
- split out code that can be reused effectively elsewhere
- wrap objects that need to be passed to other modules as a whole
- performance (EJBs are slow compared to standard beans)
- keep code shorter (per file/method) so it's easier to read and maintain
etc. etc. -
Need help with generic class with comparable type
Hi. I'm at University, and I have some coursework to do on writing a generic class which offers ordered binary trees of items which implement the comparable interface.
I cant get the code to compile which I have written.
I get the error: OBTComparable.java uses unchecked or unsafe operations
this is the more detailed information of the error when I compile with -Xlint:unchecked
OBTComparable.java:62: warning: [unchecked] unchecked call to insert(OBTType) as
a member of the raw type OBTComparable
left.insert(insertValue);
^
OBTComparable.java:64: warning: [unchecked] unchecked call to insert(OBTType) as
a member of the raw type OBTComparable
right.insert(insertValue);
^
OBTComparable.java:75: warning: [unchecked] unchecked call to find(OBTType) as a
member of the raw type OBTComparable
return left.find(findValue);
^
OBTComparable.java:77: warning: [unchecked] unchecked call to find(OBTType) as a
member of the raw type OBTComparable
return right.find(findValue);
^
and here is my code for the class
public class OBTComparable<OBTType extends Comparable<OBTType>>
// A tree is either empty or not
private boolean empty;
// If the tree is not empty then it has
// a value, a left and a right.
// These are not used it empty == true
private OBTType value;
private OBTComparable left;
private OBTComparable right;
// Create an empty tree.
public OBTComparable()
setEmpty();
} // OBTComparable
// Make this tree into an empty tree.
private void setEmpty()
empty = true;
value = null; // arbitrary
left = null;
right = null;
} // setEmpty
// See if this is an empty (Sub)tree.
public boolean isEmpty()
{ return empty; }
// Get the value which is here.
public OBTType getValue()
{ return value; }
// Get the left sub-tree.
public OBTComparable getLeft()
{ return left; }
// Get the right sub-tree.
public OBTComparable getRight()
{ return right; }
// Store a value at this position in the tree.
private void setValue(OBTType requiredValue)
if (empty)
empty = false;
left = new OBTComparable<OBTType>(); // Makes a new empty tree.
right = new OBTComparable<OBTType>(); // Makes a new empty tree.
} // if
value = requiredValue;
} // setValue
// Insert a value, allowing multiple instances.
public void insert(OBTType insertValue)
if (empty)
setValue(insertValue);
else if (insertValue.compareTo(value) < 0)
left.insert(insertValue);
else
right.insert(insertValue);
} // insert
// Find a value
public boolean find(OBTType findValue)
if (empty)
return false;
else if (findValue.equals(value))
return true;
else if (findValue.compareTo(value) < 0)
return left.find(findValue);
else
return right.find(findValue);
} // find
} // OBTComparableI am unsure how to check the types of OBTType I am comparing, I know this is the error. It is the insert method and the find method that are causing it not to compile, as they require comparing one value to another. How to I put the check in the program to see if these two are of the same type so they can be compared?
If anyone can help me with my problem that would be great!
Sorry for the long post, I just wanted to put in all the information I know to make it easier for people to answer.
Thanks in advance
DavidI have good news and undecided news.
First the good news. Your code has compiled. Those are warnings not errors. A warning is the compiler's way of saying "I understand what you are asking but maybe you didn't fully think through the consequences and I just thought I would let you know that...[something] "
In this case it's warning you that you aren't using generics. But like I said this isn't stopping it from compiling.
The undecided news is the complier is warning you about not using generics. Are you supposed to use generics for this assignment. My gut says no and if that's true then you have no problem. If you are supposed to use generics well then you have some more work. -
Why does this class not read and write at same time???
I had another thread where i was trying to combine two class files together
http://forum.java.sun.com/thread.jspa?threadID=5146796
I managed to do it myself but when i run the file it does not work right. If i write a file then try and open the file it says there are no records in the file, but if i close the gui down and open the file everything get read in as normal can anybody tell me why?
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import bank.BankUI;
import bank.*;
public class testing extends JFrame {
private ObjectOutputStream output;
private BankUI userInterface;
private JButton SaveToFile, SaveAs, Exit; //////////savetofile also saves to store need to split up and have 2 buttons
//private Store store; MIGHT BE SOMETHING TO DO WITH THIS AS I HAD TO COMMENT THIS STORE OUT TO GET IT WORKING AS STORE IS USED BELOW
private Employee record;
//////////////////////////////////////from read
private ObjectInputStream input;
private JButton nextButton, openButton, nextRecordButton ;
private Store store = new Store(100);
private Employee employeeList[] = new Employee[100];
private int count = 0, next = 0;
/////////////////////////////////////////////from read end
// set up GUI
public testing()
super( "Employee Data" ); // appears in top of gui
// create instance of reusable user interface
userInterface = new BankUI( 9 ); // nine textfields
getContentPane().add( userInterface, BorderLayout.CENTER );
// configure button doTask1 for use in this program
SaveAs = userInterface.getSaveAsButton();
SaveAs.setText( "Save as.." );
//////////////////from read
openButton = userInterface.getOpenFileButton();
openButton.setText( "Open File" );
openButton.addActionListener(
// anonymous inner class to handle openButton event
new ActionListener() {
// close file and terminate application
public void actionPerformed( ActionEvent event )
openFile();
} // end anonymous inner class
); // end call to addActionListener
// register window listener for window closing event
addWindowListener(
// anonymous inner class to handle windowClosing event
new WindowAdapter() {
// close file and terminate application
public void windowClosing( WindowEvent event )
if ( input != null )
closeFile();
System.exit( 0 );
} // end anonymous inner class
); // end call to addWindowListener
// get reference to generic task button doTask2 from BankUI
nextButton = userInterface.getDoTask2Button();
nextButton.setText( "Next Record" );
nextButton.setEnabled( false );
// register listener to call readRecord when button pressed
nextButton.addActionListener(
// anonymous inner class to handle nextRecord event
new ActionListener() {
// call readRecord when user clicks nextRecord
public void actionPerformed( ActionEvent event )
readRecord();
} // end anonymous inner class
); // end call to addActionListener
//get reference to generic task button do Task3 from BankUI
// get reference to generic task button doTask3 from BankUI
nextRecordButton = userInterface.getDoTask3Button();
nextRecordButton.setText( "Get Next Record" );
nextRecordButton.setEnabled( false );
// register listener to call readRecord when button pressed
nextRecordButton.addActionListener(
// anonymous inner class to handle nextRecord event
new ActionListener() {
// call readRecord when user clicks nextRecord
public void actionPerformed( ActionEvent event )
getNextRecord();
} // end anonymous inner class
); // end call to addActionListener
///////////from read end
// register listener to call openFile when button pressed
SaveAs.addActionListener(
// anonymous inner class to handle openButton event
new ActionListener() {
// call openFile when button pressed
public void actionPerformed( ActionEvent event )
SaveLocation();
} // end anonymous inner class
); // end call to addActionListener
// configure button doTask2 for use in this program
SaveToFile = userInterface.getSaveStoreToFileButton();
SaveToFile.setText( "Save to store and to file need to split this task up" );
SaveToFile.setEnabled( false ); // disable button
// register listener to call addRecord when button pressed
SaveToFile.addActionListener(
// anonymous inner class to handle enterButton event
new ActionListener() {
// call addRecord when button pressed
public void actionPerformed( ActionEvent event )
addRecord(); // NEED TO SPLIT UP SO DONT DO BOTH
} // end anonymous inner class
); // end call to addActionListener
Exit = userInterface.getExitAndSaveButton();
Exit.setText( "Exit " );
Exit.setEnabled( false ); // disable button
// register listener to call addRecord when button pressed
Exit.addActionListener(
// anonymous inner class to handle enterButton event
new ActionListener() {
// call addRecord when button pressed
public void actionPerformed( ActionEvent event )
addRecord(); // adds record to to file
closeFile(); // closes everything
} // end anonymous inner class
); // end call to addActionListener
// register window listener to handle window closing event
addWindowListener(
// anonymous inner class to handle windowClosing event
new WindowAdapter() {
// add current record in GUI to file, then close file
public void windowClosing( WindowEvent event )
if ( output != null )
addRecord();
closeFile();
} // end anonymous inner class
); // end call to addWindowListener
setSize( 600, 500 );
setVisible( true );
store = new Store(100);
} // end CreateSequentialFile constructor
// allow user to specify file name
////////////////from read
// enable user to select file to open
private void openFile()
// display file dialog so user can select file to open
JFileChooser fileChooser = new JFileChooser();
fileChooser.setFileSelectionMode( JFileChooser.FILES_ONLY );
int result = fileChooser.showOpenDialog( this );
// if user clicked Cancel button on dialog, return
if ( result == JFileChooser.CANCEL_OPTION )
return;
// obtain selected file
File fileName = fileChooser.getSelectedFile();
// display error if file name invalid
if ( fileName == null || fileName.getName().equals( "" ) )
JOptionPane.showMessageDialog( this, "Invalid File Name",
"Invalid File Name", JOptionPane.ERROR_MESSAGE );
else {
// open file
try {
input = new ObjectInputStream(
new FileInputStream( fileName ) );
openButton.setEnabled( false );
nextButton.setEnabled( true );
// process exceptions opening file
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error Opening File",
"Error", JOptionPane.ERROR_MESSAGE );
} // end else
} // end method openFile
public void readRecord() // need to merger with next record
Employee record;
// input the values from the file
try {
record = ( Employee ) input.readObject();
employeeList[count++]= record;
store.add(record);/////////ADDS record to Store
store.displayAll();
System.out.println("Count is " + store.getCount());
// create array of Strings to display in GUI
String values[] = {
String.valueOf(record.getName()),
String.valueOf(record.getGender()),
String.valueOf( record.getDateOfBirth()),
String.valueOf( record.getID()),
String.valueOf( record.getStartDate()),
String.valueOf( record.getSalary()),
String.valueOf( record.getAddress()),
String.valueOf( record.getNatInsNo()),
String.valueOf( record.getPhone())
// i added all those bits above split onto one line to look neater
// display record contents
userInterface.setFieldValues( values );
// display message when end-of-file reached
catch ( EOFException endOfFileException ) {
nextButton.setEnabled( false );
nextRecordButton.setEnabled( true );
JOptionPane.showMessageDialog( this, "No more records in file",
"End of File", JOptionPane.ERROR_MESSAGE );
// display error message if class is not found
catch ( ClassNotFoundException classNotFoundException ) {
JOptionPane.showMessageDialog( this, "Unable to create object",
"Class Not Found", JOptionPane.ERROR_MESSAGE );
// display error message if cannot read due to problem with file
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this,
"Error during read from file",
"Read Error", JOptionPane.ERROR_MESSAGE );
} // end method readRecord
private void getNextRecord()
Employee record = employeeList[next++%count];//cycles throught accounts
//create aray of string to display in GUI
String values[] = {String.valueOf(record.getName()),
String.valueOf(record.getGender()),
String.valueOf( record.getStartDate() ), String.valueOf( record.getAddress()),
String.valueOf( record.getNatInsNo()),
String.valueOf( record.getPhone()),
String.valueOf( record.getID() ),
String.valueOf( record.getDateOfBirth() ),
String.valueOf( record.getSalary() ) };
//display record contents
userInterface.setFieldValues(values);
//display record content
///////////////////////////////////from read end
private void SaveLocation()
// display file dialog, so user can choose file to open
JFileChooser fileChooser = new JFileChooser();
fileChooser.setFileSelectionMode( JFileChooser.FILES_ONLY );
int result = fileChooser.showSaveDialog( this );
// if user clicked Cancel button on dialog, return
if ( result == JFileChooser.CANCEL_OPTION )
return;
File fileName = fileChooser.getSelectedFile(); // get selected file
// display error if invalid
if ( fileName == null || fileName.getName().equals( "" ) )
JOptionPane.showMessageDialog( this, "Invalid File Name",
"Invalid File Name", JOptionPane.ERROR_MESSAGE );
else {
// open file
try {
output = new ObjectOutputStream(
new FileOutputStream( fileName ) );
SaveAs.setEnabled( false );
SaveToFile.setEnabled( true );
Exit.setEnabled( true );
// process exceptions from opening file
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error Opening File",
"Error", JOptionPane.ERROR_MESSAGE );
} // end else
} // end method openFile
// close file and terminate application
private void closeFile()
// close file
try {
//you want to cycle through each recordand add them to store here.
int storeSize = store.getCount();
for (int i = 0; i<storeSize;i++)
output.writeObject(store.elementAt(i));
output.close();
input.close();// from read!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
System.exit( 0 );
// process exceptions from closing file
catch( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error closing file",
"Error", JOptionPane.ERROR_MESSAGE );
System.exit( 1 );
} // end method closeFile
// add record to file
public void addRecord()
int employeeNumber = 0;
String fieldValues[] = userInterface.getFieldValues();
// if account field value is not empty
if ( ! fieldValues[ BankUI.IDNUMBER ].equals( "" ) ) {
// output values to file
try {
employeeNumber = Integer.parseInt(
fieldValues[ BankUI.IDNUMBER ] );
String dob = fieldValues[ BankUI.DOB ];
String[] dateofBirth = dob.split ("-"); // what used to put between number chnage to /
String sDate = fieldValues[ BankUI.START ];
String[] startDate = sDate.split ("-");
String sex = fieldValues[ BankUI.GENDER ];
char gender = (sex.charAt(0)); // check if m or f prob check in employee
if ( employeeNumber >= 0 ) {
/* create new record =String name, char gender, Date dob, String add, String nin, String phone, String id, Date start, float salary*/
record = new Employee(
fieldValues[ BankUI.NAME ],
gender,
new Date( Integer.parseInt(dateofBirth[0]),
Integer.parseInt(dateofBirth[1]),
Integer.parseInt(dateofBirth[2])),
fieldValues[ BankUI.ADDRESS ],
fieldValues[ BankUI.NATINTNO ],
fieldValues[ BankUI.PHONE ],
fieldValues[ BankUI.IDNUMBER ],
new Date( Integer.parseInt(startDate[0]),
Integer.parseInt(startDate[1]),
Integer.parseInt(startDate[2])),
Float.parseFloat( fieldValues[ BankUI.SALARY ] ));
if (!store.isFull())
store.add(record);
else
JOptionPane.showMessageDialog( this, "The Store is full you cannot add\n"+
"anymore employees. \nPlease Save Current File and Create a New File." );
System.out.println("Store full");
store.displayAll();
System.out.println("Count is " + store.getCount());
// output record and flush buffer
//output.writeObject( record );
output.flush();
else
JOptionPane.showMessageDialog( this,
"Account number must be greater than 0",
"Bad account number", JOptionPane.ERROR_MESSAGE );
// clear textfields
userInterface.clearFields();
} // end try
// process invalid account number or balance format
catch ( NumberFormatException formatException ) {
JOptionPane.showMessageDialog( this,
"Bad ID number, Date or Salary", "Invalid Number Format",
JOptionPane.ERROR_MESSAGE );
// process exceptions from file output
catch ( ArrayIndexOutOfBoundsException ArrayException ) {
JOptionPane.showMessageDialog( this, "Error with Start Date or Date of Birth\nPlease enter like: 01-01-2001",
"IO Exception", JOptionPane.ERROR_MESSAGE );
// process exceptions from file output
catch ( IOException ioException ) {
JOptionPane.showMessageDialog( this, "Error writing to file",
"IO Exception", JOptionPane.ERROR_MESSAGE );
closeFile();
} // end if
} // end method addRecord
public static void main( String args[] )
new testing();
} // end class CreateSequentialFileSure you can read and write at the same time. But normally you would be reading from one place and writing to another place.
I rather regret avoiding the OP's earlier post asking how to combine two classes. I looked at the two classes posted and realized the best thing to do was actually to break them into more classes. But I also realized it was going to be a big job explaining why and how, and I just don't have the patience for that sort of thing.
So now we have a Big Ball Of Tar™ and I feel partly responsible. -
Why cannnot derived class pointer point to a base class object?
Hi,
Pleaseeee... explain me why cannot the derived class pointer point to a base class object.
I know that Base class pointer can point to a derived class object.
Thanks & Regards,
Vig....Example:
class Base
{ public: void foo(); } * pBase;
class Derived : public Base
{ public: void bar(); } * pDerived;
Now, what would happen if you assign pDerived = new Base() and then call pDerived->bar()?By forbidding such an assignment, compiler prevents you from writing error-prone code. -
Can any one please tell me why this e-class is not working
Hi
I want to listen the following e-class. But its not running. Can any one please tell me why its not working
I have windows media player 11 in my system
<a href="https://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/media/uuid/34b9359e-0701-0010-f59d-ee014d5079b3?prtmode=navigate"></a>
Best Regards
Ravi Shankar BHi
I want to listen the following e-class. But its not running. Can any one please tell me why its not working
I have windows media player 11 in my system
<a href="https://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/media/uuid/34b9359e-0701-0010-f59d-ee014d5079b3?prtmode=navigate"></a>
Best Regards
Ravi Shankar B -
Why should I use abstract classes instead of a regular class with empty method bodies? Just better design? Is there some logical or performance based reason?
Why should I use abstract classes instead of aregular
class with empty method bodies? Just better design?Is
there some logical or performance based reason?Because it describes what you're doing.
If you define a "regular" class with empty message
bodies, everyone who looks at it will say "WTF is he
trying to do" or, if they're charitable, "Look,
Harvey, someone who's trying to make Java look just
like C++!".
sigh Maybe answers like THIS are why people keep asking the same question.
Here's a couple things an abstract class does that a "regular" class with empty methods bodies doesn't:
1) An abstract class cannot be instantiated.
2) An abstract class forces it's abstract methods to be implemented.
If you were to extend a non-abstract class with empty method bodies, you wouldn't have to override the methods... you could just leave them empty. An abstract class forces it.
There's a lot more reasons... those are a couple obvious ones. -
Why do we use Factory classes such BorderFactory, to get an instance of Border class, why cant we directly create an object of such classes like we do with regular concrete classes
Why do we use Factory classes such BorderFactory, to
get an instance of Border class, why cant we directly
create an object of such classes like we do with
regular concrete classesFactory methods (I mean static create methods here) have two advantages.
First, the library designer doesn't have to expose concrete classes to the outside world, just interfaces. This adds flexibility.
Second, the library designer is free to make object creations more flexible. The create method may take parameters that doesn't exactly correspond to a constructor of one specific class.
Maybe you are looking for
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