String s= new String ("Hello");
String a = new String ("Hello");
As per my understanding the first line creates 2 objects : 1 for the heap memory and 1 for String pool
2nd line : new object created and no new object created in the String pool as the keyword already exists in the pool.
So the total number of objects created after the execution of 2 lines are : 3
Which is the best way to keep track of the number of the objects I've created?Is is a good practice to have a static variable, which will be incremented everytime I call a contructor?
Class circle{
private double x,y,radius;
private static count;
Circle(double x1, double y1, double radius1){
x=x1;y=y1;radius=radius1;
count++;
}
how many objects got created at each line (in String pool or in Objects memory):
public class Test {
public static void main(String[] args) {
String s1 = "test";
String s2 = new("test");
String s3 = s1 + s2;
StringBuider sb = new StringBuilder().append(s2);
}
}
I am little confused about String creation in java.
Doubt 1: How String objects assigned to Pool area:
1. String s="in pool";
2. String s1= new String("not in pool");
How many objects created in statement 1 and 2. According to recent discussion with my colleague, one object created in String pool in case 1. And in case 2, two objects are created, one as literal goes to String pool and other with new() opr goes to Heap.
If above is correct, Ain't we wasting double memory for same object ? Really need clear understanding on this
Doubt 2: How does intern() work: Please see if my below explanation is correct
1. If String literal is already present in String pool , and i create a same string with new operator, reference to object is changed to pool area.
2. If String object is created using new operator and intern is called on it. If same string object is not present in the String Pool, Its moved to String pool and reference to this in Pool is returned.
I am currently working on a project where I need to return data from a database over RMI to a client who requests it. Some of the fields in the Data Object can not be seen by the client so I need to create another object to send over the network instead. The method I use is this...
public static SerializableObject createSerializableObjectFromDataObject(DataObject dataObject){
SerializableObject serializableObject = new SerializableObject();
serializableObject.setField(dataObject.getField());
serializableObject.setAnotherField(dataObject.getAnotherField());
return serializableObject;
}
Is there a better way of doing this? I am creating many subclasses DataObject which all require this static method to be implemented and I can't push it into the superclass because each one needs custom behaviour.
How should I access object, which I have created in servlet? Servlet handles the requests(controller) and forwards to requested jsp page.Some of the jsp pages need EJB objects. When i create an ejb object in servlet and then forward the request to jsp, how can i access the object in jsp ? This should be MVC - based application, like JSP-Servlet-EJB.
View Replies View RelatedIs it possible to have the value of an entered String to be set as the name of the String to be created whilst running.For example: String username= Keyboard.readString() & the user entered for example the word: "Hello".Is there a way how I can make the Java Program create another String named Hello (Inputted value of String username).
If this is allowed, what do I have to use and if possible show me exactly what I have to do with the example mentioned above?
cm2yOUa.jpg
Write a piece of code that would change something in the one of the buttons created using the loop? I have spent few hours reading about the arrays, different methods and can't think or apply a working solution.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class C2loops extends JFrame implements ActionListener {
private JButton jBTile, jBClicker;
private JPanel jPLeft, jPRight;
[Code] ....
I have started working on a little project in my free time. It is just a simple text rpg that runs in a counsel window. I have 5 files each file contains 1 class.
public class SomnusCharacter {
private String gender = "";
private int age = 0;
private String race = "";
private int level = 0;
private int xp = 0;
[Code] ....
The chain of events right now is:
1. MainMenu is run
2. If user inputs n CreateCharactor is run
3. User inputs name, age, ect in SomnusCharacter object made in CreateCharacter
4. Intro (just rough demo for testing purposes) is run
5. If user inputs m Menu is run
6. Menu calls and prints out all the information from the object made in CreateCharacter
Step 6 is where I am having my problems. How can I reference (lets say the SomnusCharacter object made is called player) player from my Menu class? I know that if I made a new character that it would just create another SomunsCharacter object with the default values again.
I have create as short example which contains two classes Cat and Dog followed by a switch statement in the main method.
Class Cat
public class Cat {
private String name;
//Setter
public void setName(String pName)
{name = pName;}
//Getter
public String getName()
{return name;}
// Constructor
public Cat(String catName)
{name = catName;}
[code]....
My Issue is that after creating the objects within the switch statement, is there a way to return the objects back to the main method once created within the switch ?
I have a situation where I have 2 classes and an array of objects which are causing me trouble.
The object type is one I have created - it is made from a class which is neither of the 2 classes I previously mentioned.
The array is created and occupied in Class1 and the problem arises when I try to reference one of the element from Class2.
At first I forgot the the array would be local to Class1.main so I made the array a global variable using:
Java Code: public MyObjectType[] myArray; mh_sh_highlight_all('java');
Then I tried accessing an element (2) from Class2 using:
Java Code: Class1.myArray[2] mh_sh_highlight_all('java');
However I get errors saying that I can't access the static variable from a non-static context.
I understand a little bit about static and non-static objects/methods but don't know how to fix this. Do I need to include "static" in the array declaration?
I have a method that checks to see if a file exists, if so, it reads the data contained therein, if not it calls another method then exits.
public void checkLoadPreviousStationStatus() throws FileNotFoundException, IOException,
ClassNotFoundException, EOFException, TempArrayOutOfBoundsException{
File f = new File(staFileName);
//if station file already exists load the info
if(f.exists() && !f.isDirectory()){
[Code] ....
My question, do I need to delete this file before exiting the method f.delete();? If not, what happens to it when I exit the method?
Memory recalled from a long ago taken c++ class: It's just reserving a memory location that will or will not be used isn't it? If nothing is stored in that location the reservation goes away right?
I am working on an independent project it is a simple little text based rpg that will run in a counsel window. I have an object for Character that is creating during a CreateCharacter method. I want the play to be able to enter a character that will open up a menu that displays things like the name and health and stuff of the character from the object created in CreateCharacter, but because I have it in a different class I don't know how to reference the object made in CreateCharacter.
I have it in 6 files
Character --- Object with getters/setters for things like name, age, race, class, ect
MainMenu --- Displays title and promts for new game and quit
CreateCharacter --- Walks through and sets all values in Character
Stats --- Keeps the players stats (health, attack, ect) in an array
Intro --- Beginning demo thing (not really important for this question)
Menu --- Displays all current user stats (Having issues with this one)
Example I have this in Menu
System.out.println("Name: " + ????.getName());
I'm trying to write a program where a new window/frame is created when a certain key in entered, here F1. It doesn't seem to be working..
I've done it using JApplet. Here are the functions:
String msg="";
int X=10, Y=20;
public void init()
{
addKeyListener(this);
}
public void keyPressed(KeyEvent ke)
[Code] .....
I have been going over my code line by line, over and over again for nearly and hour now...When I execute method `file.createNewFile()`, the method returns true and throws no exceptions. It even says that the file exists. However, the file is not created and cannot be accessed until the program has exited.
File portLib = new File("");
private class RememberPortAction extends AbstractMenuItemAction
{
methods...
protected void actionPerformed() {
LibraryCreator creator = new LibraryCreator(self, logger);
File newPortLib;
[code]....
I have one Project -"A".Inside of that I use, .XLS to read data.
Structure - A/src/TestData
Inside of the TesetData - I have placed XLS files.
I have main method in TestDriver class.If I run this in Eclipse, running fine.But after exported to executable/runnable Jar, and ran via command line (command - jar -jar myjar.jar), I see issue: "Exception in thread "main" java.io.FileNotFoundException: srcTestDataTestCaseController.xls"
public static void main(String[] args)
throws Exception
{
ResultSet rs;
rs = readExcelData(testControllerName, sheetName, "");
}
As I use main() method which is static, I am getting error if I write like the below:
public void getXls(){
String testControllerName ="TestCaseController.xls"
TestDriver.getClass().getClassLoader().getResource (testControllerName);
}
How to read/access the XLS, after I exported as runnable jar
How does jsp create session when there're two requests coming simultaneously from the same client browser(maybe one tab maybe two tabs)?
I ask this question because it is said jsp could solve DuplicateSessionException in flex.
[URL] ....
if so, jsp would create same session(with same session id) for the two requests coming simultaneously?
Why query string is not getting created in doPost method of HttpServlet?Is this reason is enough - it is supplying data in html body.
View Replies View RelatedWhen does HTTP Session object is created in web application. Suppose I have a website. Home page of website is HTTP page which contains details of company and link to Login page.
Consider below mentioned user journey as scenario:
a. user arrives at home page of website
b. user click on Login page
c. user fill in login details on login page and click on Submit
d. user is successfully authenticated and authorized from back end
e. User specific page is shown
f. user click on logout link
g. user is successfully logged out from website
h. user is redirected to home page
i. user closes browser
In the above mentioned user journey,
a. at which step does HTTP session starts (means at which steps does HTTP Session object is created ? )
b. at which step does HTTP session ends ?
In case required, assume tech stack to be Java 7, Servlet 2.5, JSP, Tomcat 7, Apache web server (for static web contents).....
So I am working on an ABV calculator for some practice, and one problem I am running into is that I am unable to set a JLabel properly on the top of the window that is created. It will display the text with no problem, but only on one column. Is there a way to center a JLabel across 2 columns? The label I am working with is titleL.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.text.DecimalFormat;
public class Beer_Calculator extends JFrame
[Code] .....
coding the action listener for my button (btBody) which create button displaying 1 to 9 in a nested for loop; the button should allow the user to click on them and to display the number clicked on in a JTextField;my code;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class EX_7_2 extends JFrame
{
public EX_7_2()
{
setLayout(new BorderLayout(5, 10));
[code]....
Sometimes models needs to access blocking devices, like network cards, databases, files, and so on. This should be done by worker threads or services. But who is in charge of that? The controller or the model itself? I tend to say it is the model, as only the model knows about the fact that it accesses a blocking object. On the other hand, it is said that a model should be a POJO, so it would be the controller's job. Is there a best practice or general design rule?
View Replies View RelatedI have created a DefaultTableModel tablel as a Global variable. The table is then created and attached to a Grid bag layout. Then I want to call the table again in another method to add rows of data into it. Hopefully that makes sense.
So the addrow for the table is located in the final method private class CalcButtonListener implements ActionListener
When I debug the code, deftablemodel variable is carrying NULL data.
Also to make things even more complicated, The actual headers for the table aren't showing up,... not entirely sure why though.
import java.awt.BorderLayout;
import javax.swing.*;
import java.awt.event.*;
import java.awt.Dimension;
import javax.swing.JOptionPane;
import javax.swing.JMenuBar;
[code]....
My code below creates the 2 files successfully, but it is not able to write the sample data into the newly created file. I can't figure out the reason why.
Another strange thing is that when I tried inserting System.out.println calls for debugging, nothing prints out.
try{
// stuff here
}
catch(FileNotFoundException fileNF){
String dirString = System.getProperty("user.dir");
String defaultFile = "config";
String currentFile = "currentconfig";
Path filePath = Paths.get(dirString, defaultFile);
Path filePath2 = Paths.get(dirString, currentFile);
[Code]...
The question pretty much says it all, but I tasked myself with creating a program about lemurs. There are multiple class files in this program. In the below code snippet, I have my TreeLemur.class which extends to the Lemur.class which extends to the Mammal.class. However, when I create a Tree Lemur object in the main program, it is returning null consistently from certain methods. What am I doing wrong here?
TreeLemur.class :
public class TreeLemur extends Lemur {
private String groupSize;
private String diet;
private String fur;
public void setGroupSize() {
groupSize = "
Group Size: Large";
}
[Code]...
As of yet, I'm just trying to get Tree Lemur working properly to continue with creating the other if-branches within the main program.
I am trying to restrict the number of views in JSF 2.0.2 using
<context-param>
<param-name>org.apache.myfaces.NUMBER_OF_VIEWS_IN_SESSION</param-name>
<param-value>5</param-value>
</context-param>
In my case my managed bean is View Scoped and it supports a UI page which has multiple forms and each form is submitted as AJAX POST request.
As per the statndard, setting restriction to 5 should create 5 views and after that based on LRU algorithm the oldest views should get deleted if 6th views is created.
Therefore any action on the oldest view will throw the ViewExpiredException and i simply redirect the user to view expired page.
1) When i set the restriction to 5 views, i open 4 tabs with 3 forms each.
2) I submit the 3 forms on first tab everything works fine.
3) As soon as I go to 2nd tab and submit the first form thr, i get view expired exception
4) It seems I am exceeding the number of views I mentioned in web.xml
I want to know :
1) Does every AJAX POST submit itself creates a view ?
2) How I can count the number of views created in a session ?
3)Can i force expiry of a view in JSF 2.0.2 while the session is still alive ?
4) Normally JSF 2.0.2 session cachces the views. Lets assume session is alive the entire day but a view was created in morning at 9:00 AM and is not used again the entire day. Assuming that session doesn't reaches the max number of views it can save in entire day, will the view created in morning expire on its own after certain interval of time ? If not , can we still force its expiry while keeping the session alive ?