Java is a high-level, platform-independent, object-oriented programming language originally developed by Sun Microsystems. Java is currently owned by Oracle, which purchased Sun in 2010.

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4
votes
3answers
243 views

Why use arg type `class Object` instead of `Comparable[]`?

In the code below, I believe it would look more appropriate to make the method argument be of type Comparable[] instead of Object[]. The first reason it would be more appropriate is that one can be ...
0
votes
1answer
107 views

Is it possible to have a keyed dictionary stored on disk? [closed]

for example) would it be possible to be able to use the key of an item to access the item stored in a file out on disk (without searching through the whole file)? I'm looking fora general example of ...
0
votes
1answer
82 views

Matrices calculations on partial shape matching

I'm working in a shape recognition project where it is supposed for me to develop an application that receives two images: an original one and a sketch made by a user. I am supposed to detect contours ...
0
votes
2answers
150 views

Develop GUI and logic in a team the right way? [closed]

I am planning to start a small project with a friend. I will be developing the GUI using JavaFX in the MVC pattern and he will be responsible for the model/logic. My question is: how can we achieve a ...
0
votes
1answer
25 views

Using classes not designed for multiple sessions in servlet

I'm looking for a way to use a collection of Java classes in a servlet, which would provide some services to clients, but the classes were not designed with multiple sessions in mind, which seems to ...
0
votes
1answer
72 views

Can JUnit be used to test this project?

I currently have an interesting situation occurring with my code, and after hacking away at what turned out to be a dead end for the last two weeks, I'm here asking those smarter than I to educate me ...
2
votes
1answer
111 views

Is Singleton enough for a EMailUtil or there is any better implementation? [duplicate]

I am developing an application, where I have to send lots of emails for user account creations, validation, invites etc. I have implemented a static class EMailUtil which has different methods like ...
2
votes
1answer
62 views

Creating/updating entity save strategy

Please note: although I'm talking about Java in this question, what I'm asking about here should really be language-agnostic. I am dabbling in OR/M for the first time, and have cooked up the ...
1
vote
1answer
279 views

Programmatically extending Hibernate table/entity definitions in Spring, how?

I would like to know if there is a way —maybe with AOP— to extend table/entity definitions so that I can add functionality across the board that requires persistence. Let me explain what I want to do ...
3
votes
4answers
278 views

Why is the hashCode method usage of HashSet not specified in the API?

I was trying to debug my code which uses a HashSet and searching through the SO, I found out that I needed to override the hashCode method as well. The strange part is, checking the related API, I did ...
1
vote
2answers
121 views

Improve the speed of a Tomcat Server with MySQL

I'm developing an application with 3 sides, desktop (JavaFX), server (Tomcat) and Android. And a MySQL Database Server. The app receive mails and convert them into tasks. The tasks are sent to the ...
1
vote
1answer
175 views

Creating a calendar/planner program. Confused about OO logic?

I'd like to create a piece of software that has the functionality of a common written planner. To do this, it will have a Calendar. When planning the program, I became confused as to how I would ...
1
vote
3answers
197 views

Building a calculator using MVC

I've been programming in Java for about 6 months, and I thought a good and challenging test of my skills would be to build a GUI calculator. I have very recently heard about this MVC idea, and I ...
0
votes
2answers
120 views

Managing multiple JDBC connection

I have an application that connects to databases based on a json string that contains connection information. The json is sent just when the application starts. How do you manage such connection ...
0
votes
1answer
137 views

Is Default Package included in the Package Level Access?

I would like to know how the default package is defined in Java.I know how public and private access is defined but I don't know whether there is any default package access that is defined in package ...
-1
votes
1answer
183 views

Whether Methods could be defined in Constructors in Java? [closed]

I am learning to program in Java and have run into a situation I don't understand. I have this code import java.io.*; class temp { temp() { Finish f=new Finish(); f.end(); } ...
-3
votes
1answer
65 views

Why are there just a few implementations of a Java EE container? [closed]

I see at the JCP that work on Java EE 8 is allready in progress, as Java EE 7 was released almost 1,5 year ago. However, as far as I know there are only three implementations of the Java EE 7 ...
-3
votes
1answer
121 views

What is immutable by default in Java? [closed]

While trying to grasp copying/copy constructors, and noticed that some things seem to be immutable by default (Strings, and Integers), while everything else is mutable by default. That leaves me ...
3
votes
2answers
122 views

What preconditions should be checked while adding/removing a listener?

Imagine the following interface: interface Service { addListener(Listener l) removeListener(Listener l) } Should I check for null values while add/remove? Is it a good idea on remove to ...
4
votes
1answer
170 views

What is the advantage of 'SwingUtilities.invokeLater()' method?

For the below sample GUI program using javax.swing, public class UnResponsiveUI extends JFrame{ private boolean stop = false; private JTextField tfCount; private int count = 1; /* ...
0
votes
2answers
189 views

Using Constructors in Java

I would like to know why do we need to use constructors in examples like this:http://math.hws.edu/eck/cs124/javanotes5/c5/s2.html. I think even if there are no constructors the programs mentioned in ...
0
votes
0answers
31 views

What does 'name' attribute signify in any java.awt component?

With the below program, am trying to find the names assigned to all the components part of the GUI. public class AWTCounter extends Frame implements ActionListener{ private Label lblCount; ...
2
votes
1answer
123 views

Java App as Tomcat Service?

I currently have a basic j2ee website. Currently, a jsp frontend gets data from the backend (the java program, lets call it object "Score"). The backend gets this data from a web site. <% Main m ...
3
votes
1answer
103 views

Why 'JButton' is-a 'Container' in javax.swing?

As per the class hierarchy in java.awt.*, class Button & class Label is-a class Component, and Component is not a Container, which make sense to me. As per the redesign of class hierarchy in ...
0
votes
1answer
22 views

Query on usage of 'Window()' default constructor from java.awt

I had been through this query before asking this question. In class Window we have constructor with default direct access level package private but not private as shown below: Window() throws ...
1
vote
4answers
151 views

Is there an alternative to instanceof when filtering a Java stream by class?

I have an unexpected situation in a project in which all types extending one class are packed into a Java collection; but only a specific extension of that class contains an additional method. Let's ...
3
votes
1answer
166 views

Type Casting in Java

Could anyone explain why short(100000) is -31072 as said in p.48 of java-notes.The article says that "the value -31072 is obtained by taking the the 4 byte int 100000 and throwing away two of these ...
1
vote
2answers
198 views

Most Efficient way to Compute the sum of divisors of N (1 ≤ N ≤ 1 000 000 000)

I want to write a code which computes the sum of divisors of a number N(1 ≤ N ≤ 1 000 000 000), excluding the number itself. However, I need an efficient way to do it. It suppose to print the answer ...
1
vote
2answers
57 views

Query on Recursive composition

For the below relation between Container and Componentin java.awt class hierarchy, I see that, in addition to is-a relation, class Container has composite relation with class Component with below ...
0
votes
1answer
78 views

Does class Availability makes programming as Object Oriented Language? [duplicate]

Does class Availability makes programming as Object Oriented Language ? Most of the people think that if there is Availability Class in a language, then that language becomes Object Oriented. Is it ...
2
votes
2answers
205 views

architecture of database heavy application

A program I'm currently designing is extremely database heavy, almost anything the user does will alter the database, or read from it. Now I have one interface which defines all these operations, and ...
0
votes
1answer
102 views

Starting Execution of Java Program [duplicate]

While reading about Java Programming I couldn't get why it states Java static main necessity reason is because "before you're program starts,there aren't any objects to send messages to" as said in ...
0
votes
6answers
234 views

Why 'String' objects are immutable with an explicit constructor in java? [duplicate]

It make sense to make class String objects immutable with following declarations, because they share the same storage in common pool. String str1 = "abc"; String str2 = "abc"; But, am not sure, if ...
0
votes
2answers
278 views

Where is it specified that Java is call by value?

I know that Java is by default call-by-value but I am not sure where in the Java Language Specification this is addressed. Google searching only seems to find me unofficial sources but never points to ...
0
votes
0answers
64 views

Transaction Management in Hibernate with DAO Design Pattern

I have many Tables, For every Table,we have DAO Interface and DAOImplementation class. Example DAO Interface public interface CancelPolicyDAO { public CancelPolicy insertCancelPolicy(CancelPolicy ...
1
vote
2answers
185 views

Are there other ways to limit recursion depth for a function?

I am trying to prevent a function/method (in Java) from performing recursion more than a depth of 3 self calls. I've learnt about the accumulator trick from odersky's scala coursera course. public ...
11
votes
4answers
721 views

Why shouldn't a method throw multiple types of checked exceptions?

We use SonarQube to analyse our Java code and it has this rule (set to critical): Public methods should throw at most one checked exception Using checked exceptions forces method callers to ...
2
votes
1answer
96 views

Simple and Composite transactional services: Question about separation of concerns and transactions

I believe I know the answer to this but I'm looking for any holes or anything I may be missing. This is focused on Spring and Java but could really apply to any programming stack. Anyway, we have a ...
0
votes
0answers
34 views

Design architecture and software for webapp integrating with few other endpoints (Email Server, Jira, CRM system)

In my upcoming project, I need to integrate a webapp with few other endpoints. Main duty of the webapp will be some kind of thin-client for inner JIRA system for company. Moreover, I'll need to ...
0
votes
2answers
111 views

Java Web Application in Cluster with Shared Database. How to Negotiate an Instance to do Updates? How to Notify Instances of Updates? [duplicate]

I have a Java web application, running in a cluster of Tomcat application servers and a shared SQL/JDBC database. Data from the database is cached in memory in each instance of the web app. My web ...
0
votes
4answers
225 views

How to ensure objects unique by equality?

I frequently have this problem but didn't find it as an established programming pattern. I have some Class C whose equality is determined by some key k and I want to prevent time-consuming ...
1
vote
2answers
152 views

Can I use US-ASCII and UTF-8 encoding interchangeably for an XML file without a XML root declaration?

My source XML does NOT contain the root declaration i.e. <?xml version="1.0" encoding="utf-8" ?> And when I run the file command on it, I get: ASCII text, with very long lines, with CRLF ...
0
votes
1answer
140 views

calculating the average of a value over a month [closed]

I am working on a project right now that is having me calculate monthly interest on a bank account. The way the interest is supposed to be calculated is as follows: Use the daily average to calculate ...
0
votes
1answer
203 views

Did Java avoid multiple inheritance here?

I learnt that Java did not allow multiple inheritance using abstract classes for simplicity. In java, after a good design of class hierarchy, SubType would not get into trouble of same method ...
0
votes
1answer
234 views

Why does this evaluation function work in a connect four game in java

I am exploring how a Minimax algorithm can be used in a connect four game. I was looking through a program and found this evaluation function. private static int[][] evaluationTable = {{3, 4, 5, 7, ...
1
vote
4answers
167 views

Java exception handling design

I am trying to design a simple exception handling strategy for web services middleware using some ideas from here: http://northconcepts.com/blog/2013/01/18/6-tips-to-improve-your-exception-handling/. ...
2
votes
2answers
154 views

Passing by value multiple times vs. Creating a public class variable

Suppose I have a series of methods across different classes that all use the same five core variables defined in my main method. I could chain these five variables as method arguments from one method ...
0
votes
3answers
243 views

I want to understand clearly why can't we instantiate an object of an abstract class [duplicate]

Can I get a clear explanation why why can't we instantiate an object of an abstract class. I know abstract is not real. But I want to know more why can't we instantiate an object of an abstract class. ...
4
votes
3answers
233 views

Batching immutable object changes?

With immutable models, what would be the best way to batch several changes? For example, let's have a Book that is immutable. I need to change both title and year. I could change one by one, but that ...
0
votes
3answers
264 views

Java 1.7 library with a Java 1.5 program - what are the options

I have a class library which is compiled with JDK 1.7 It uses several 1.7 features and classes and would be very difficult to get it recompiled in JDK 1.5. This needs to integrate with an old legacy ...