In singleton pattern just having a static field is not enough? Do we really need to have a private constructor?
I can have a static field and have a public constructor and still say it is singleton.
I have heard about using patterns in core java.Is it possible?If yes, how?
View Replies View RelatedI've got a problem in Eclipse. The below code is a part of my program, used for (re)starting a new game. The 'public static int' statement gives the error 'This method must return a result of type int'..
public static int playAgain(){
boolean validInput = false;
do {
System.out.println("Would you like to play a game? Please answer 'yes' or 'no'.");
String playAgain = input.next();
[Code] ....
Why is the logic not correct with the method public static boolean containsColor(String color, Circle [] ca)? It only returns me only false values.
Java Code: public class Circle {
private double radius;
private String color;
public Circle()
{
radius = 1;
color = "red";
[code]....
java com.brainbench.TestCommandLine -p Parameter1 Parameter2 Parameter3 Parameter4 ..
If the user enters the command line shown above, how many elements are contained in the array which is passed to "public static void main(String args[])" in TestCommandLine?
Choice 1 Four
Choice 2 Five
Choice 3 Six
Choice 4 Seven
Choice 5 Nine
I need to add an additional field (called client). When I try to do this, I get the "no suitable constructor found" error. I don't understand what I am doing wrong or where else to look.
package com.voxware.impl.wem.reports;
import net.sf.jasperreports.engine.JRDataSource;
import net.sf.jasperreports.engine.data.JRBeanCollectionDataSource;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
[Code] ....
I'm not really sure I understand the functional difference between a static and final variable/field. Oracle defines Class Variable as:
Class Variables (Static Fields) A class variable is any field declared with the static modifier; this tells the compiler that there is exactly one copy of this variable in existence, regardless of how many times the class has been instantiated. A field defining the number of gears for a particular kind of bicycle could be marked as static since conceptually the same number of gears will apply to all instances. The code static int numGears = 6; would create such a static field. Additionally, the keyword final could be added to indicate that the number of gears will never change.
If static will have the same value regardless of how many times it's used, then why use final (or vice versa)?
What is serialization in Java ?how to use serialization in Singleton?
View Replies View RelatedIf i am correct, a singleton class is the one for which only one object is allowed to create right. so why can't i just use everything in that as static and access them using the class name ? what is the need to create a single object ?
View Replies View RelatedI've found following code for Singleton Implementation from this forum, I am having a difficulty of understanding following,
1. When Singleton instance will be created, ( From which call ) ?
2. What feature of Static Inner class allow object to be singleton ?
3. How Inner Class implementation is thread safe ?
4. What will happen if variable "instance" mark as non-static, Will it still grantee singleton implementation ?
Java Code:
public class Singleton {
// Note private constructor
private Singleton() {}
private static class SingletonInner {
private final static Singleton instance = new Singleton();
}
public static Singleton getInstance() {
return SingletonInner.instance;
}
} mh_sh_highlight_all('java');
I want to create a singleton for DirContext for LDAP configuration, hence i have used the initialize on demandclass holder idiom as shown below
public class SlmApplicationContext {
/**
* inner class to hold the instance.
*/
private static class Holder {
private static DirContext instance = new InitialDirContext();
}
/**
* Method to get the singleton instance of this class.
* @return SlmApplicationContext
*/
public static SlmApplicationContext getInstance() {
return Holder.instance; }
...
}
Now the problem is if i close the DirContext.close(), when the next request comes the singleton wont work as the dir context is already closed, hence it will create a new dir context for each requests. Which breaks the singleton concept, hence how we can ensure the singleton works fine even with DirContext.close()?
This is my code inside the method:
@Post
public static String getDetails(Representation entity) throws Exception {
String customerId = getQuery().getValues("cus_id");
}
I use this code in Restlet Representation. I try to get the value from the Request API. But I am facing the problem as "Cannot make a static reference to the non-static method getQuery() from the type Resource".
From what i understand static methods should be called without creating an instance of the same class . If so why would they return an instance of the same class like in the following : public static Location locateLargest(double[][] a) , the Location class being the same class where the method is defined . I don't understand this , does it mean that every field and every method in the class must be static ? Meaning that you cannot have instances of the class because everything is static . Or it's just a mistake and the class Location cannot have a static method: public static Location locateLargest(double[][] a) ?
View Replies View RelatedI can't figure out what this error message "Cannot make a static reference to the non-static method getEndUserCharge(long, long, long, long) from the type UpdateUserWS" actually means.
The error is coming from:
public void updateDetailsPackage() {
some unrelated code
long zero=0;
double endUserCharge=0;
endUserCharge = UpdateUserWS.getEndUserCharge(long zero, long zero, long zero, long zero); <-------- error is here
[Code] ....
Alright, I have two classes, this one
public class Player {
private String player;
public String getPlayer() {
return player;
}
private int strength;
private int defense;
[Code] .....
However, it says that under Player.getPlayer() that it 'Cannot make a static reference to the non-static method'.
When I browsed I came to know two ways of implementing singleton.. I dont know which is best.. I am implementing this to load resource bundle only once for my jvm using constructor to getBundle.
public class bundle {
private final static Logger LOGGER = Logger.getLogger(bundle .class.getName());
private static bundle instance;
private static ResourceBundle messages;
private bundle () {
messages = ResourceBundle.getBundle("pb", Locale.getDefault());
[Code] ....
and I am calling this as bundle.getInstance.getMessage("hi");I wanted to knw which option is better and why.. and in the second case how can i call the getMessage() method?
I made UpdateInmateDisplayer a Singleton so that I could access it from the private class ButtonHandler. It works to display the first inmate's number on the screen but when I close out the window and click the Book Inmate button in CurInmatesDisplayer again, it only shows a blank window. I've tried adding the components again from the ButtonHandler in CurInmatesDisplayer but it doesn't work.
View Replies View RelatedWhy I can create an Instance of a class that contains non static variables within the static main method ?
This program runs fine
import java.util.*;
public class Test{
public int j;
public static void main(String[] args) {
Test test1=new Test();
System.out.println(test1.j);
[Code] .....
I am trying to call an actionListener which is shown below in my PSVM :
class testMenuItemListener implements ActionListener {
public void actionPerformed(ActionEvent arg0) {
getContentPane().removeAll();
createPanel();
getContentPane().add(panel1); //Adding to content pane, not to Frame
repaint();
printAll(getGraphics()); //Extort print all content
[Code] .....
I get the following error :
Frame.java:409: error: non-static variable this cannot be referenced from a static context
menuItem1.addActionListener(new testMenuItemListener());
I am trying to add a field (called special) to a hibernate table. I am copying existing code (related to the NAME field) so I don't have to figure this out from scratch. I am getting the error
"[ERROR] C:VOXvoxware-1.1.13voxwarevoxware-implsrcmainjavacomvoxwareimplflowVoxFlowConfiguration.java:[213,38] error: non-static variable special cannot be referenced from a static context".
Line 213 is in public void mergeFrom, the actual line is "special = VoxFlowConfiguration.special;" I don't understand why Java thinks special is a "non-static" variable but it doesn't have a problem with the other variables (such as name, orderShow)
package com.voxware.impl.flow;
import com.voxware.asset.LiabilityType;
import com.voxware.flow.FlowConfiguration;
import com.voxware.flow.OrderFlow;
import com.voxware.flow.Step;
import com.voxware.i18n.LanguageCodes;
import com.voxware.impl.i18n.UTF8Control;
import com.voxware.impl.persistence.BaseEntity;
import com.voxware.impl.portal.VoxPortal;
[code]....
I'm working on a banking program that is supposed to use 3 classes (Account-base class, CheckingAccount, and SavingsAccount) and several methods to display the banking information (ID, balance after a withdrawal and deposit, and the annual interest rate). This should be a pretty simple program, but I'm getting hung up on one portion of it. I'm getting some compiler errors, all of which deal with non-static variables being called from a static context (I'll also post these errors following the code). Up until the middle of last week, we just declared everything as static, but that's changed and I'm having trouble figuring out when to and when not to use static when declaring my methods, hence the compiler errors.
import java.util.Date;
public class Account {
private int id = 0;
private double balance = 0;
private double annualInterestRate = 0;
private Date dateCreated = new Date();
[Code] ....
Here are the compiler errors I am receiving:
Compilation completed. The following files were not compiled:
6 errors found:
File: C:UsersHiTechRedneckDesktopSummer II 2014Computer Programming PrincipleProgram 5CheckingAccount.java [line: 7]
Error: non-static method getId() cannot be referenced from a static context
[Code] .....
I am trying to call an actionListener which is shown below in my PSVM :
class testMenuItemListener implements ActionListener
{
public void actionPerformed(ActionEvent arg0) {
getContentPane().removeAll();
createPanel();
getContentPane().add(panel1); //Adding to content pane, not to Frame
repaint();
[Code] .....
I get the following error :
Frame.java:409: error: non-static variable this cannot be referenced from a static context
menuItem1.addActionListener(new testMenuItemListener());
I am writing the following program in Java SE 7. It throwing "Cannot make a static reference to the non-static type String" . However if I write parameterised String inside main method as java.lang.String[] args, it compiles fine.
class MainClass<String> {
<T> MainClass(T t) {
System.out.println(t.getClass().getName());
}
public static void main(String[] args) {
System.out.println("asdasd");
new MainClass<>("");
}
}
I mean following programs compile fine in Java SE 7 :
class MainClass<String> {
<T> MainClass(T t) {
System.out.println(t.getClass().getName());
}
public static void main(java.lang.String[] args) {
System.out.println("asdasd");
new MainClass<>("");
}
}
My assignment was to create a simple form that demonstrates the use of the factory and singleton design patterns. "Use the Factory pattern to ensure that each form input consists of a text label and a textfield. Use the Singleton pattern for the submit button. When the submit button is clicked, a pop-up should show all the information that was typed into all of the form fields."
I used JFrame to create the form without the design patterns and I although I get the desired result, I'm not quite sure how I can integrate the design patterns into the code I wrote. The example I have to go off uses shapes, not text fields so I think that's why I'm not quite clear on how to approach this.
Here's my code so far:
import javax.swing.event.*;
import javax.swing.*;
import java.awt.*;
[Code]....
My assignment was to create a simple form that demonstrates the use of the factory and singleton design patterns. "Use the Factory pattern to ensure that each form input consists of a text label and a textfield. Use the Singleton pattern for the submit button."
Here's what I have:
Form.java file
interface Form {
public void getFormField ();
}
Name.java file (I have a similar files just like this for Address.java, City.java, State.java, Zip.java and Phone.java)
import java.util.Scanner;
class Name implements Form
[Code] ....
It compiles at the moment but I get a null pointer exception in the main method of the FormFactoryDemo file.
i am trying to make something, and i want to request input from user and it shoud look like this
1. xxx -> press 1 to choose this
2. xxx -> press 2 to choose this
So if they enter 3 or string or whatever i want to restart method and show again
1. xxx -> press 1 to choose this
2. xxx -> press 2 to choose this
So here is method that i am trying to restart
public static void askUser(){
System.out.println("xxx");
System.out.println("1. xxx");
System.out.println("2. xxx");
System.out.println("3. xxx");
[code]....
If i try to make it public void than it say can't call non-static methods inside static(main).if i try to put it into new class and then call it after i fail input it goes into infinite loop.