Override hashCode() method
hi,
I'm writing a very simple hashCode() function (3different way), which uses 2 string to calculate the hashCode, it looks somethings like this:
1)...
public int hashCode() {
str1 = "abc"; //Can be replaced by any string
str2 = "cde"; //Can be replaced by any string
return (str1 + str2).hashCode();
}2...
public int hashCode() {
str1 = "abc"; //Can be replaced by any string
str2 = "cde"; //Can be replaced by any string
return (str1 + "-----" + str2).hashCode();
}3...
public int hashCode() {
str1 = "abc"; //Can be replaced by any string
str2 = "cde"; //Can be replaced by any string
return (str1.hashCode() + str2.hashCode());
}For 1 (similar for 2) if we have str1 + str2 = str1' + str2', then it will returns the same hashcode, which is I dont want...
But for 3, will that results in clustering? What are the bad things about 3?
Thanks
I don't have any problem at the moment, I am just asking for opinion on the good and bad thing of each of those implementation on hashCode().
My equals() methods is pretty obvious, if str1 = str1' and str2 = str2' then return true.
The str1 & str2 can change.
Anyway, let me put in the whole class code:
public class MyClassTest {
private final String str1;
private final String str2;
public MyClassTest(final String s1, final String s2) {
str1 = s1;
str2 = s2;
public String getStr1() {
return str1;
public String getStr2() {
return str2;
public boolean equals(Object anotherMyClassTest) {
if (anotherMyClassTest instanceof MyClassTest) {
MyClassTest id = (MyClassTest) anotherMyClassTest;
if (id.getStr1().equals(this.getStr1()) && (id.getStr2().equals(this.getStr2()))) {
return true;
return false;
public int hashCode() {
//See the 3 implementation below
}and then, there was three way of implementing the hashCode()
1)...
public int hashCode() {
return (str1 + str2).hashCode();
2...
public int hashCode() {
return (str1 + "-----" + str2).hashCode();
3...
public int hashCode() {
return (str1.hashCode() + str2.hashCode());
}This MyClassTest will then be used inside a HashMap as the key (and there can be many of these)
And my question is: Which of the 3 implementation is the best, and could you explain to me the good/bad thing of each of those 3 implementation?
Thanks
Message was edited by:
Gurluver
Message was edited by:
Gurluver
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Can u pls tell me friends why should definetly i override the hashcode method if i override equals method of the Object class
Because the contracts of equals and hashCode are strongly bound to each other.
For each objects x and y where x.equals(y) returns true x.hashCode() must be equal to y.hashCode().
If you don't follow this convention you'll get hard-to-find bugs as soon as you use your object as a key in some kind of HashMap/HashTable/... -
When we override Hashcode and Equal Methods
Hi....I have doubt regading Hashcode and equal methods
why we override this two methods....
why we override hashcode method when we are overriding equal method,
i would very thankful to give answser
Thank you
Rameshhash code is computed to check the equality of two
objects ,
that is why if u change the default equal method
implementation , u need to change the hashcode method
as well.That's an incomplete answer at best.
The hashcode method is used by hashing algorithms and data strcutures such as HashMap. This value is used to determine what 'bucket' the reference will go into. It cannot, by itself determine equality.
If you are still unsure, I suggest looking up 'hash table' on google. I'm sure there's a decent explanation on wikipedia. -
...is not abstract and does not override abstract method compare
Why am I getting the above compile error when I am very clearly overriding abstract method compare (ditto abstract method compareTo)? Here is my code -- which was presented 1.5 code and I'm trying to retrofit to 1.4 -- followed by the complete compile time error. Thanks in advance for your help (even though I'm sure this is an easy question for you experts):
import java.util.*;
This program sorts a set of item by comparing
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public class TreeSetTest
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public int compare(Item a, Item b) // LINE CAUSING THE ERROR
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An item with a description and a part number.
class Item implements Comparable
Constructs an item.
@param aDescription the item's description
@param aPartNumber the item's part number
public Item(String aDescription, int aPartNumber)
description = aDescription;
partNumber = aPartNumber;
Gets the description of this item.
@return the description
public String getDescription()
return description;
public String toString()
return "[descripion=" + description
+ ", partNumber=" + partNumber + "]";
public boolean equals(Object otherObject)
if (this == otherObject) return true;
if (otherObject == null) return false;
if (getClass() != otherObject.getClass()) return false;
Item other = (Item) otherObject;
return description.equals(other.description)
&& partNumber == other.partNumber;
public int hashCode()
return 13 * description.hashCode() + 17 * partNumber;
public int compareTo(Item other) // OTHER LINE CAUSING THE ERROR
return partNumber - other.partNumber;
private String description;
private int partNumber;
}Compiler error:
TreeSetTest.java:25: <anonymous TreeSetTest$1> is not abstract and does not over
ride abstract method compare(java.lang.Object,java.lang.Object) in java.util.Com
parator
public int compare(Item a, Item b)
^
TreeSetTest.java:41: Item is not abstract and does not override abstract method
compareTo(java.lang.Object) in java.lang.Comparable
class Item implements Comparable
^
2 errorsAccording to the book I'm reading, if you merely take
out the generic from the code, it should compile and
run in v1.4 (assuming, of course, that the class
exists in 1.4). I don't know what book you are reading but that's certainly incorrect or incomplete at least. I've manually retrofitted code to 1.4, and you'll be inserting casts as well as replacing type references with Object (or the erased type, to be more precise).
These interfaces do exist in 1.4, and
without the generics.Exactly. Which means compareTo takes an Object, and you should change your overriding method accordingly.
But this raises a new question: how does my 1.4
compiler know anything about generics? It doesn't and it can't. As the compiler is telling you, those interfaces expect Object. Think about it, you want to implement one interface which declares a method argument type of Object, in several classes, each with a different type. Obviously all of those are not valid overrides. -
How to override hashcode() in String
I need to override the hashcode() method in java.lang.String with a cyclic shift hash code. how do I do this? String is final so I cannot extend it. I've looked at all the postings regarding the logic of why hashcode() must be overwritten with equals() etc, but I need some thoughts on how to actually override the method.
public class MyString { // you are right, you can't extends java.lang.String
private String str; // but you can wrap it
public MyString(String s) {
this.str = s;
public String get() {
return this.str;
// ... implement all or most String methods again ...
// ... then ...
public int hashcode() {
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}--lichu -
How to enforce developers to override toString() method
Hi,
Right now we are in design stage of our application. I want that all our BO classes should override toString(), equals() and hashCode() methods.
We expect that our application would be running for next 5 to 10 years, and so looking for ways to enforce these rules to developers.
One way to do is let ant script handle such validations. Another way could be using PMD to enforce rules.
These could be good ways of doing this, but my manager doesnot quite like to depend on external tools like these ... as 5 years down the line you donot know state of these tools.
Can someone suggest if java provides any such provision ...
If someone has some smart solution do let me know ... your help is much appreciated ... and thanks in advance.
Regards,
Rana BiswasThis is interesting.
toString() method is already implemented in class Object, which is inherited by all other class.
What happens if we make toString() method abstract. I tried it and compiler allows to do it ... was wondering if it would have any side effect.
Regards,
Rana Biswas -
Why should we overide hashCode method when we overide equals ?
Why should we overide hashCode method when we overide equals ?
java.lang.Swapnil wrote:
Why should we overide hashCode method when we overide equals ?For the purpose of hashing, you need to override both hashcode and equal method. It is because different objects(in most cases) have different hashcode.
Edited by: Hunky322 on 28.?ub.2009 16:21 -
Comparing dynamic fields of objects using equals and hashCode methods
To compare the different objects of the same class with their contents like jobTitleId, classificationId, deptId & classificationId was to be done and do some manipulations later using Set and Map. I was able to do that by simply overriding the equals and hashCode methods of Object class and was able to fetch the information (like in the following Map).
Map<LocationData, List<LocationData>>
The following is the class I used (its been shown to you so that it can be referred for my problem statement):
LocationData class
package com.astreait.bulkloader;
public class LocationData {
String locId, deptId, jobTitleId, classificationId;
@Override
public boolean equals(Object obj) {
LocationData ld = (LocationData)obj;
return this.deptId.equals(ld.deptId) && this.jobTitleId.equals(ld.jobTitleId) && this.classificationId.equals(ld.classificationId) &&
this.locId.equals(ld.locId);
@Override
public int hashCode() {
return deptId.hashCode() + jobTitleId.hashCode() + classificationId.hashCode() +locId.hashCode();
Problem:
I'm already known to which all fields of this object I need to make the comparison.
i.e I'm bound to use the variables named classificationId, deptId, jobTitleId & locId etc.
Need:
I need to customize this logic such that the fields Names (classificationId, deptId, jobTitleId & locId etc) can be pulled dynamically along with their values. So, as far as my understanding I made use of 2 classes (TableClass and ColWithData) such that the List of ColWithData is there in TableClass object.
I'm thinking what if I override the same two methods `equals() & hashCode();`
such that the same can be achieved.
TableClass class #1
class TableClass{
List<ColWithData> cwdList;
@Override
public boolean equals(Object obj) {
boolean returnVal = false;
// I need to have the logic to be defined such that
// all of the dynamic fields can be compared
return returnVal;
@Override
public int hashCode() {
int returnVal = 0;
// I need to have the logic to be defined such that
// all of the dynamic fields can be found for their individual hashCodes
return returnVal;
ColWithData class #2
class ColWithData{
String col; // here the jobTitleId, classificationId, deptId, locId or any other more fields info can come.
String data; // The corresponding data or value for each jobTitleId, classificationId, deptId, locId or any other more fields.
Please let me know if I'm proceeding in the right direction or I should make some any other approach. If it is ok to use the current approach then what should be performed in the equals and hashCode methods?
Finally I need to make the map as: (Its not the concern how I will make, but can be considered as my desired result from this logic)
Map<TableClass, List<TableClass>> finalMap;Hello,
What is the relation with the Oracle Forms tool ?
Francois -
Dear Members :
I have custom hashCode method in conjunction with overriden equals method, in my program and have following doubts/observations :
[1] In order to verify whether the hashCode method is executed, I put a println statement within method, but this doesn't output when the program is run.
[2] The program is a simple equality testing of two dates and doesn't make use of any map. I want to know when and who gives (implicit ?) call to this hashCode method, when equals method is overriden, I mean the program flow.
Since SUN suggests to override hashCode, whenever equals method is overriden, and my program is not making use of map, how and when the hashCode method gets called and if so why my test print is not executed ?
Thanks in advance.
Atanuuj_ wrote:
jverd wrote:
uj_ wrote:
One way to graciously avoid the contract is to override hashCode and let it throw an exception (or assertion) stating "hashCode not implemented. This class is not intended for use in hash-based collections" or something.What would be the advantage of doing that over just taking the 5 minutes needed to implement it properly?Who are you to stipulate other people's design needs? Just because something takes just 5 minutes doesn't mean it's the right thing to do.
You may want a class to have an equals relation based on content but you still may not want the class to be in a hash-based collection. The most compelling reason may be that it's not immutable.
The equals/hashCode contract is mostly a Sun promise regarding "standard" classes. Everybody else design their classes the way they see fit.Calm down UJ. I have as much right to offer my opinion as you have to offer yours. I just asked a simple question.
The requirement that a class not be used in a hash-based collection would be silly. It's up to the user of the class how to store instances. If the fields that go into determining hashCode are mutable, then that should be a documentation issue. There are good reasons to keep hashCode and equals in sync. The only reason not to do so would be the time it takes to write the code. Since that time is trivial for any well-designed class, it's an extremely weak reason. -
How to write overridden hashcode method? Is there any particular rule for it?
Folks,
It is not required that if two objects are unequal according to the equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hashtables. My two bobs worth is... I'm a simple kind of idiot... I struggle with all the double negatives in Object.hashCode API. So here's my rewrite.
The equals and hashCode methods share a special relationship.
The general contract is:
1. If two objects are equals they must have the same hashCode.
2. BUT, If two objects have the same hashCode they don't necessarily have to be equals, but this is called "a hashCode clash", which ain't good. A poor hashCode implementation (one which produces a high proportion of "clashes") dramatically slows-down hashMap lookups. In hash-code-land: More distincter is more betterer.
3. Both equals and hashCode must be consistent over time. The hashCode must remain unchanged unless an attribute effecting equals has changed... at which time the hashCode proabably should change (but see rule 2).
The rules of thumb for developers are:
1. The equals and the hashCode methods should examine the same attributes of the object.
2. So... If you override hashCode you almost certainly need to override equals to fulfill the above contract.
2. And vice versa: If you override equals you probably need to override hashCode to fulfill the above contract.
And what the API should say but doesn't is that hashCode only affects Hash* collections (those which begin with the word "Hash") such as HashTable, and HashMap. If you're not using Hash* collections (and are positive that your objects will never be stored in a Hash* collection) then you can get away with totally ignoring hashCode and all of it's innate complexities; with the Caveat Emptor that surety is inversely proportional to the magnitude of the universe of discourse... so you're better off just doing it, coz it's easier than evaluating the consequences of NOT doing it.
Just my two bobs worth.
Cheers. Keith. -
When using HashSet or LinkedHashSet, the objects you add to them
must override hashCode().[u]Why ??
I think Object.hashCode() returns hashcode of an object and two different objects can have same hashCode.
So if i have to use HashSet or LinkedHashSet,do i need to override hashCode() in such a way so that it provides different hashcode for different objects so as to avoid duplicate objects in a HashSet (Serving the purpose of HashSet)HashSet is backed by a hash table (i.e. uses the
hashCode to organize its data), allowing
good/constant performance for theadd/remove/contains
methods by using (I guess) binary search (seeHashMap
for details?)No, TreeSet and -Map use a binary search. Internally,
they are backed up by a Red-Black tree (a
"self-balancing" binary tree).Oh right, mea culpa, the HashSet (HashMap) uses a "direct" hashcode-to-bucket mapping, then linear search throughout the bucket (which explains why hashCode implementation/dispersion is of some importance.) -
Is not abstract and does not override abstract method actionPerformed
I dont how to corr. Please help!! and thank you very much!!
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class test extends JFrame implements ActionListener, ItemListener
private CenterPanel centerPanel;
private QuestionPanel questionPanel;
private ButtonPanel buttonPanel;
private ResponsePanel responsePanel;
private JButton b1,b2,b3,b4,b5; //Create five references to Jbutton instances
private JTextField t1,t2,t3,t4,t5; //Create five references to JTextField instances
private JLabel label1; //Create one references to JLabel instances
private JRadioButton q1,q2,q3; //Create three references to JRadioButton instances
private ButtonGroup radioGroup; //Create one references to Button Group instances
private int que1[] = new int[5]; //Create int[4] Array
private int que2[] = new int[5];
private int que3[] = new int[5];
private String temp1, temp2, temp3, temp4, temp5, temp6, temp7, temp8, temp9, temp10,
temp11, temp12, temp13, temp14, temp15;
public test (String header)
super(header);
Container container = getContentPane();
label1 = new JLabel ("PLease click on your response to ");
q1 = new JRadioButton("I understand most of the content of this subject",true);
add(q1);
q2 = new JRadioButton("I see the relevance of the subject to my degree",false);
add(q2);
q3 = new JRadioButton("The workload in this subject is appropriate",false);
add(q3);
radioGroup = new ButtonGroup(); //JRadioButton belong to ButtonGroup
radioGroup.add(q1);
radioGroup.add(q2);
radioGroup.add(q3);
JPanel buttonPanel = new JPanel();
JPanel responsePanel = new JPanel();
JPanel questionPanel = new JPanel();
JPanel centerPanel = new JPanel();
b1 = new JButton ("Strongly DISAGREE"); //Instantiate JButton with text
b1.addActionListener (this); //Register JButtons to receive events
b2 = new JButton ("DISAGREE");
b2.addActionListener (this);
b3 = new JButton ("Neither AGREE or DISAGREE");
b3.addActionListener (this);
b4 = new JButton ("AGREE");
b4.addActionListener (this);
b5 = new JButton ("Strongly AGREE");
b5.addActionListener (this);
buttonPanel.setLayout(new GridLayout(5,1));
buttonPanel.add(b1);
buttonPanel.add(b2);
buttonPanel.add(b3);
buttonPanel.add(b4);
buttonPanel.add(b5);
t1 = new JTextField ("0",3); //JTextField contains empty string
t2 = new JTextField ("0",3);
t3 = new JTextField ("0",3);
t4 = new JTextField ("0",3);
t5 = new JTextField ("0",3);
t1.setEditable( false );
t2.setEditable( false );
t3.setEditable( false );
t4.setEditable( false );
t5.setEditable( false );
responsePanel.setLayout(new GridLayout(5,1));
responsePanel.add(t1);
responsePanel.add(t2);
responsePanel.add(t3);
responsePanel.add(t4);
responsePanel.add(t5);
questionPanel.setLayout(new GridLayout(4,1));
questionPanel.add(label1);
questionPanel.add(q1);
questionPanel.add(q2);
questionPanel.add(q3);
centerPanel.add(buttonPanel,BorderLayout.CENTER);
centerPanel.add(responsePanel,BorderLayout.EAST);
container.add(centerPanel,BorderLayout.WEST);
container.add(questionPanel,BorderLayout.NORTH);
q1.addActionListener(
new ActionListener(){
public void actionPerformed( ActionEvent e )
{ //actionPerformed of all registered listeners
if (e.getSource() == b1) {
que1[0] = Integer.parseInt(t1.getText()) + 1;
String temp1 = String.valueOf(que1[0]);
t1.setText(temp1);
else if (e.getSource() == b2) {
que1[1] = Integer.parseInt(t2.getText()) + 1;
String temp2 = String.valueOf(que1[1]);
t2.setText(temp2);
else if (e.getSource() == b3) {
que1[2] = Integer.parseInt(t3.getText()) + 1;
String temp3 = String.valueOf(que1[2]);
t3.setText(temp3);
else if (e.getSource() == b4) {
que1[3] = Integer.parseInt(t4.getText()) + 1;
String temp4 = String.valueOf(que1[3]);
t4.setText(temp4);
else if (e.getSource() == b5) {
que1[4] = Integer.parseInt(t5.getText()) + 1;
String temp5 = String.valueOf(que1[4]);
t5.setText(temp5);
} //end action performed
q2.addActionListener(
new ActionListener(){
public void actionPerformed( ActionEvent e )
{ //actionPerformed of all registered listeners
if (e.getSource() == b1) {
que2[0] = Integer.parseInt(t1.getText()) + 1;
String temp6 = String.valueOf(que2[0]);
t1.setText(temp1);
else if (e.getSource() == b2) {
que2[1] = Integer.parseInt(t2.getText()) + 1;
String temp7 = String.valueOf(que2[1]);
t2.setText(temp7);
else if (e.getSource() == b3) {
que2[2] = Integer.parseInt(t3.getText()) + 1;
String temp8 = String.valueOf(que2[2]);
t3.setText(temp8);
else if (e.getSource() == b4) {
que2[3] = Integer.parseInt(t4.getText()) + 1;
String temp9 = String.valueOf(que2[3]);
t4.setText(temp9);
else if (e.getSource() == b5) {
que2[4] = Integer.parseInt(t5.getText()) + 1;
String temp10 = String.valueOf(que2[4]);
t5.setText(temp10);
} //end action performed
q3.addActionListener(
new ActionListener(){
public void actionPerformed( ActionEvent e )
{ //actionPerformed of all registered listeners
if (e.getSource() == b1) {
que3[0] = Integer.parseInt(t1.getText()) + 1;
String temp11 = String.valueOf(que3[0]);
t1.setText(temp11);
else if (e.getSource() == b2) {
que3[1] = Integer.parseInt(t2.getText()) + 1;
String temp12 = String.valueOf(que3[1]);
t2.setText(temp12);
else if (e.getSource() == b3) {
que3[2] = Integer.parseInt(t3.getText()) + 1;
String temp13 = String.valueOf(que3[2]);
t3.setText(temp13);
else if (e.getSource() == b4) {
que3[3] = Integer.parseInt(t4.getText()) + 1;
String temp14 = String.valueOf(que3[3]);
t4.setText(temp14);
else if (e.getSource() == b5) {
que3[4] = Integer.parseInt(t5.getText()) + 1;
String temp15 = String.valueOf(que3[4]);
t5.setText(temp15);
} //end action performed
}//end constructor test
public void itemStateChanged(ItemEvent item) {
//int state = item.getStateChange();
//if (q1 == item.SELECTED)
public class ButtonPanel extends JPanel
public ButtonPanel()
public class CenterPanel extends JPanel
public CenterPanel()
public class QuestionPanel extends JPanel
public QuestionPanel()
public class ResponsePanel extends JPanel
public ResponsePanel()
public static void main(String [] args)
test surveyFrame = new test("Student Survey") ;
surveyFrame.setSize( 500,300 );
surveyFrame.setVisible(true);
surveyFrame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
}//end main
}//end class testis not abstract and does not override abstract method actionPerformed
Oh, I see that the title of your post is an error message? Ok. Well, the test class is declared as implementing an ActionListener. That means the test class must have an actionPerformed() method. Your test class apparently does not.
It does not appear that the test class needs to implement ActionListener. You are using annonymous classes as listeners. -
Is not abstract and does not override abstract method tablechanged
I will remove all the gui code to make it shorter, but my problem lies with my InteractiveTableModelListener.
public class Meet extends JPanel{
private static void createAndShowGUI() {
JFrame frame = new JFrame("MEET_dataTable");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new Meet(), BorderLayout.CENTER);
frame.pack();
frame.setVisible(true);
public class InteractiveTableModelListener implements TableModelListener {
public void TableChanged(TableModelEvent evt) {
if (evt.getType() == TableModelEvent.UPDATE) {
int column = evt.getColumn();
int row = evt.getFirstRow();
dataTable.setColumnSelectionInterval(column + 1, column + 1);
dataTable.setRowSelectionInterval(row, row);
class InteractiveRenderer extends DefaultTableCellRenderer {
protected int interactiveColumn;
public InteractiveRenderer(int interactiveColumn) {
this.interactiveColumn = interactiveColumn;
public Component getTableCellRendererComponent(JTable dataTable,
Object value, boolean isSelected, boolean hasFocus, int row,
int column)
Component c = super.getTableCellRendererComponent(dataTable, value, isSelected, hasFocus, row, column);
if (column == interactiveColumn && hasFocus) {
if ((Meet.this.tableModel.getRowCount() - 1) == row &&
!Meet.this.tableModel.hasEmptyRow())
Meet.this.tableModel.addEmptyRow();
highlightLastRow(row);
return c;
public void highlightLastRow(int row) {
int lastrow = tableModel.getRowCount();
if (row == lastrow - 1) {
dataTable.setRowSelectionInterval(lastrow - 1, lastrow - 1);
else {
dataTable.setRowSelectionInterval(row + 1, row + 1);
dataTable.setColumnSelectionInterval(0, 0);
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
UIManager.put("swing.boldMetal", Boolean.FALSE);
createAndShowGUI();
}As i say, i have removed all the gui code to make it shorter, but in this code i create the table and add all the model to it. I am being returned with the error
Meet.InteractiveTableModelListener is not abstract and does not override abstract method tableChanged(javax.swing.event.TableModelEvent)in javax.swing.event.TableModelListener
what would be causing this error?
CheersSorry, just figured out my silly error, the method is tableChanged not TableChanged.
cheers
TOPIC CLOSED
Edited by: nick2price on Sep 11, 2008 7:08 AM -
Is not abstract and does not override abstract method ERROR
Hello. I'm new at all this, and am attempting to recreate a sample code out of my book (Teach Yourself XML in 24 Hours), and I keep getting an error. I appriciate any help.
This is the Error that I get:
DocumentPrinter is not abstract and does not override abstract method skippedEntity(java.lang.String) in org.xml.sax.ContentHandler
public class DocumentPrinter implements ContentHandler, ErrorHandler
^This is the sourcecode:
import org.xml.sax.Attributes;
import org.xml.sax.ContentHandler;
import org.xml.sax.ErrorHandler;
import org.xml.sax.Locator;
import org.xml.sax.SAXParseException;
import org.xml.sax.XMLReader;
public class DocumentPrinter implements ContentHandler, ErrorHandler
// A Constant containing the name of the SAX parser to use.
private static final String PARSER_NAME = "org.apache.xerces.parsers.SAXParser";
public static void main(String[] args)
// Check to see whether the user supplied any command line arguments. If not, print an error and exit.
if (args.length == 0)
System.out.println("No XML document path specified.");
System.exit(1);
// Create a new instance of the DocumentPrinter class.
DocumentPrinter dp = new DocumentPrinter();
try
// Create a new instance of the XML Parser.
XMLReader parser = (XMLReader)Class.forName(PARSER_NAME).newInstance();
// Set the parser's content handler
// parser.setContentHandler(dp);
// Set the parsers error handler
parser.setErrorHandler(dp);
// Parse the file named in the argument
parser.parse(args[0]);
catch (Exception ex)
System.out.println(ex.getMessage());
ex.printStackTrace();
public void characters(char[] ch, int start, int length)
String chars ="";
for (int i = start; i < start + length; i++)
chars = chars + ch;
System.out.println("Recieved characters: " + chars);
public void startDocument()
System.out.println("Start Document.");
public void endDocument()
System.out.println("End of Document.");
public void startElement(String namespaceURI, String localName, String qName, Attributes atts)
System.out.println("Start element: " + localName);
for (int i = 0; i < atts.getLength(); i++)
System.out.println(" Attribute: " + atts.getLocalName(i));
System.out.println(" Value: " + atts.getValue(i));
public void endElement(String namespaceURI, String localName, String qName)
System.out.println("End of element: " + localName);
public void startPrefixMapping(String prefix, String uri)
System.out.println("Prefix mapping: " + prefix);
System.out.println("URI: " + uri);
public void endPrefixMapping(String prefix)
System.out.println("End of prefix mapping: " + prefix);
public void ignorableWhitespace(char[] ch, int start, int length)
System.out.println("Recieved whitespace.");
public void processingInstruction(String target, String data)
System.out.println("Recieved processing instruction:");
System.out.println("Target: " + target);
System.out.println("Data: " + data);
public void setDocumentLocation(Locator locator)
// Nada
public void error(SAXParseException exception)
System.out.println("Parsing error on line " + exception.getLineNumber());
public void fatalError(SAXParseException exception)
System.out.println("Fatal parsing error on line " + exception.getLineNumber());
public void warning(SAXParseException exception)
System.out.println("Warning on line " + exception.getLineNumber());Check to make sure that the arguments are consistent with your ContentHandler class. Probably the wrong type.
I think you forgot to include the skippedEntity method, it seems to be missing. Even if an implemented class has a method that you are not using, you still have to include the method in your code even if it doesn't do anything.
Message was edited by:
ChargersTule1 -
Product is not abstract and does not override abstract method
Received the following errors.
Product.java:3: Product is not abstract and does not override abstract method ge
tDisplayText() in Displayable
public class Product implements Displayable
^
Product.java:16: getDisplayText() in Product cannot implement getDisplayText() i
n Displayable; attempting to use incompatible return type
found : void
required: java.lang.String
public void getDisplayText()
^
2 errors
Code reads as follows
import java.text.NumberFormat;
public class Product implements Displayable
private String code;
private String description;
private double price;
public Product()
this.code = "";
this.description = "";
this.price = 0;
public void getDisplayText()
String message =
"Code: " + code + "\n" +
"Description: " + description + "\n" +
"Price: " + this.getFormattedPrice() + "\n";
public Product(String code, String description, double price)
this.code = code;
this.description = description;
this.price = price;
public void setCode(String code)
this.code = code;
public String getCode(){
return code;
public void setDescription(String description)
this.description = description;
public String getDescription()
return description;
public void setPrice(double price)
this.price = price;
public double getPrice()
return price;
public String getFormattedPrice()
NumberFormat currency = NumberFormat.getCurrencyInstance();
return currency.format(price);
Please help!Received the following errors.
Product.java:3: Product is not abstract and does not
override abstract method ge
tDisplayText() in Displayable
public class Product implements Displayable
^
Product.java:16: getDisplayText() in Product cannot
implement getDisplayText() i
n Displayable; attempting to use incompatible return
type
found : void
required: java.lang.String
public void getDisplayText()
^
2 errors
Code reads as follows
Please use the code tags when posting code. There is a code button right above the text box where you enter your post. Click on it and put the code between the code tags.
These error messages are quite clear in telling what is wrong. You have an Interface called Displayable that specifies a method something like thispublic String getDisplayText() {But in your Product source code, you created thismethodpublic void getDisplayText() {The compiler is complaining because the methods are not the same.
You also need to return a String in the method probalby like thisreturn message;
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