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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242 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 ...
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2answers
203 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 ...
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1answer
145 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 ...
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1answer
184 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(); } ...
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1answer
74 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 ...
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1answer
125 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 ...
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2answers
126 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
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1answer
246 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; /* ...
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2answers
192 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 ...
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1answer
70 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
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1answer
127 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
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1answer
115 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 ...
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1answer
23 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 ...
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4answers
210 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
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1answer
168 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
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2answers
252 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 ...
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2answers
69 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 ...
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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
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2answers
214 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 ...
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1answer
104 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 ...
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6answers
247 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
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2answers
297 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 ...
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0answers
87 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 ...
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2answers
249 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 ...
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4answers
1k 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
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1answer
102 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 ...
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0answers
60 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 ...
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2answers
144 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 ...
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4answers
230 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 ...
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2answers
177 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 ...
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1answer
175 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
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1answer
212 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 ...
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1answer
319 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, ...
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4answers
188 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
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2answers
182 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 ...
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3answers
471 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
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3answers
243 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 ...
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3answers
273 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 ...
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1answer
100 views

Help Understanding This? [closed]

I'm using the book Heads First Java and I just don't understand it at some parts and the book doesn't explain it well enough. Could someone please tell me what each line does? public class whileloop ...
3
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1answer
72 views

Skeletal/Abstract class just to store shared state?

Given an interface for the Strategy pattern like so: public interface Strategy { public Output execute(Input input); public Output getLastExecutionOutput(); } if I want to store the last ...
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1answer
105 views

What is the purpose of Deprecation? [closed]

Is it just giving different names to previously named method? Does it change with the language you use? Is it essential? I have noticed different APIs having deprecated methods, which actually seem ...
2
votes
0answers
126 views

How to pass control between sub-controller to parent controller in Java MVC Design Pattern?

I'm pretty new in Java, but I've done plenty of research and I know what MVC is. However, to implement MVC in Java was a difficult task. I followed this tutorial, which helped me to realise that the ...
0
votes
1answer
115 views

How do different technologies connect to form a web stack? [closed]

I am a little confused, is it possible to implement a front end using common languages like html, css and javascript and then do server side processing using a language of your choice, say python or ...
5
votes
2answers
510 views

Why can't I understand Java? [closed]

I'm a 9th grader and I joined my school's robotics team in order to learn how to code Java and enter the programming team. However, I am so confused! Even after the first lesson, I had no idea what ...
3
votes
1answer
118 views

Should a class explicitly implement interface if its superclass also implements it?

Given an interface interface I { one(); two(); } An abstract base class partially implementing I abstract class A { @Override void one() { //something } } And lastly ...
0
votes
4answers
773 views

Why 'List<E>' is an 'interface' but not 'abstract class'?

While defining the hierarchy, one can think to embed the abstract method(behaviour) in abstract class only because the derive concrete class posses that as core behaviour with it's specific ...
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2answers
328 views

Programming against interfaces in Java

Supposing I have an interface Foo and a given implementation FooImpl. public class FooImpl implements Foo If I want to define a new operation on this class that depends on the particular ...
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2answers
379 views

Is factory pattern a right pattern for the situation described here?

Is factory pattern a right pattern when we want to consolidate the related objects? Problem - In the Set-top box, I have a user-io, basically the interface to control the settop box - The user-io can ...
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5answers
255 views

Race conditions in JVM languages versus C/C++

I was thinking about thread synchronization issues in compiled languages like C++, versus synchronization issues in languages like Java. I'm wondering how a JVM language like Java doesn't (at least ...
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5answers
760 views

Coding style issue: Should we have functions which take a parameter, modify it, and then RETURN that parameter?

I'm having a bit of a debate with my friend over whether these two practices are merely two sides of the same coin, or whether one is genuinely better. We have a function which takes a parameter, ...