Questions tagged [java]

Java (not to be confused with JavaScript) is a class-based, object-oriented, strongly typed, reflective language and run-time environment (JRE). Java programs are compiled to bytecode and run in a virtual machine (JVM) enabling a "write once, run anywhere" (WORA) methodology.

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Implementation of Gitlab CI + Docker + Spring Boot

i would really appreciate if anyone could invest a bit of time to review what i did. Basically this is first time i do this, and that is reason why i need another set of eyes. I have Spring Boot ...
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Android component animatable on its height

I'd like to have a code review for a component which is supposed to be animatable on its height. It's supposed to be a transitioning element. I find it quite laggy on my phone. ...
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Pseudo-parallel depth-first search

I'm writing a small program that generates a file containing an adjancency matrix, it then reads from that file, constructs a graph and does something like a parallel depth-first search (dfs) on it. ...
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Implement two level caching using spring's cache abstraction Cache and CacheManager

Details about spring's caching framework are here. When I was reading this link, I thought the composite cache mentioned there was one that used levels of caching based on the order given to the ...
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1answer
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Recursively merge n-level maps of values and lists

I was looking for a solution for a way to easily merge maps of serialized Yaml and came up with this. Reference to a similar question (not asked by me): https://stackoverflow.com/questions/25773567/...
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Python version of Clean Code book example

I started reading Robert Martin's Clean Code. I'm trying to "translate" all his examples into Python, so I can understand them better since my domain on Python is greater than on Java. ...
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448 views

Mahjong hand completeness checking algorithm

As a summer project, I have been working on a small-scale, console-based version of Mahjong (the Rummy-like hand completion game, and not the solitaire version). While having prior knowledge of the ...
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Android audio recording using AudioRecord and ByteBuffer

I'm developing an audio recorder app for android using AudioRecord class to have a low level access to audio samples. ...
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215 views

A Java neural network

I have created a neural network in Java, it contains multiple classes. I have uploaded the documentation for the network here: Doxygen, and the full source can be found on Github. Let me start out by ...
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Writing service/network layer for mobile apps

I have an app that gets and posts blog posts to and from a server. Right now I have a network client object which is passed into a service object. The service object is created and called from an ...
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127 views

User role Observable

I have a service with these methods: Observable<User> getUsers(); Observable<Role> getUserRoles(String userId); For each user, I want to get her ...
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Using the same RecyclerView.Adapter with a different ViewHolder

I would use the same RecyclerView.Adapter with two or more different fragments. Every fragment uses a different view items layout so I must use a different ...
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Just a digital clock in Swing

I've written a little clock implementation in Java Swing. It now seems to work flawlessly after having terrible Swing specific timing problems. Please indicate if this is the way to draw the clock and ...
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Fragment of code with Android MVP that checks login credentials via REST API

I'm learning MVP for Android and am wondering if that piece of code that I wrote is correct in terms of this pattern or maybe is completely messed up. I'm wondering if there can be return type other ...
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75 views

Game of Life, thread per cell

In an effort to learn Java's support for concurrency I solved a self-imposed exercise to write a Game of Life simulator in Java, running a separate thread for each cell. Here is my code: ...
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Parsing HTTP request for webserver implementation

I'm writing a web server from scratch on pure Java in learning purpose. As a part of request handling, I worked on a class to parse HTTP request, I expect from it to be able to do next things: ...
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71 views

Extracting cycles from directed graph with max degree 1 and then performing set cover on cycles

I'm trying to solve P1243E in an efficient manner. The problem in simple words is: Given \$k\$ boxes, \$i\$-th box with \$n_i\$ numbers. All numbers are distinct. We need to select one number from ...
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138 views

Java multithreading many readers one writer implementations

I have a shared data object with writer threads and reader threads. Number of threads can read from the shared data at the same time (in the code getmethod), and ...
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541 views

RGB to YCbCr conversion in Java

I found a Go language code to do RGB to YCbCr conversion from here! I ported it to Java: ...
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912 views

Mouse wheel scrolling for nested scrollable Swing components

By default, mouse wheel scrolling in Java Swing behaves differently than in web browsers. In Swing, when you have an inner scrollable component and an outer scrollable component, the mouse wheel ...
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Data processing program

I'm working on part of a service for data processing. The main idea of the service is to get the input data, process it and return the processed data to another service. Input and output data format ...
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451 views

Parallel solutions to N Queens Puzzle

I'm trying to increase the performance of my N Queens Puzzle solution. I'd find some threads on SO already but they don't appear to help me to increase performance. My best solution, however, is a ...
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Optimizing Graph Algorithms for Floyd Warshall and Johnson Algorithm

I am trying to implement and compare Floyd Warshall and Johnson Algorithm(for Sparse Graphs). I have written the following code which produces correct output values for the all pair shortest paths. ...
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213 views

Implementing a tabular pretty-print using Java 8 Stream API

About six years ago I implemented a simple tabular pretty-print Java class that mostly simulated MySQL CLI query result tables. I don't really like it because it was implemented in a, I believe, ...
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91 views

Biometric data representation in Java

This code represents biometric data averaged over a 1min period, beginning at the given UTC time. Please review my code: ...
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158 views

Algorithm to find connected tiles (percolation)

I wrote a little program in JavaFX which displays a path of neighbouring open tiles going from top to bottom. It should simulate a percolation. The algorithm iterates through the whole grid (every ...
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Updating the UI without leaking the context after an Android AsyncTask finishes

In the past I always did AsyncTasks as private inner classes. The tutorials I found still recommend this (see here, here, here, and here). However, this has the potential to leak the context. Now ...
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Simple MVC CRUD with JDBC

I would like to review my simple piece of code. I am beginner (I learn java for 1 year) and I would like to find out whether I am on good way. I have created simple MVC CRUD java app "ProductManager"....
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Instantiating an animal using fluent classes with inheritance

I've spent a couple of weeks implementing a simple text editor. The entire program uses only immutable objects and a functional, fluid programming style. After reading about ways to implement Fluent ...
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Dynamically creating login screen on Android devices

This has been an experience. I'm well above "hello world" java is not a language I use often when programming and I don't program too much. I find myself a lot on Google.... basically just about for ...
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218 views

SAP BPM API - Fetching ProcessInstance & TaskAbstract

I am using SAP BPM API's to fetch currently running process instance and the task belonging to the running process instance. I have return below method on an EJB Class which does the job, however it ...
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91 views

Simplified Google Maps program

I've been trying to write a simplified Google Maps program. My programming experience is limited. I have come up with a solution but I'm looking to make it more user friendly by splitting it up into ...
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159 views

Simple Brainf_ck IDE in JavaFX 8

I have this simple IDE for playing with Brainf_ck. It has no file functionality; only the code, input and output fields are present, and the "compiler" is integrated. Here is how it looks like: My ...
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JavaFX Scene Video Capture Utility

2 days ago as I was working on my game I decided I wanted to include some sort of a video showing sneak peaks of the themes and tutorials and such. I then decided to check how to record my scene or ...
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Integer tree sort in Java

I have this algorithm for sorting integer arrays. Basically, it's a balanced tree sort which creates a tree node for each distinct integer, and in each tree node it maintains a counter counting how ...
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133 views

Hash Based Data Structure in Java for Collision Calculation

I have started a project on my free time were I'm writing a 2D game engine in Java. One of the more challenging and interesting aspects of such a project is collision detection between sprites on the ...
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Building a tree structure from pairs of parent-child to retrieve all ancestors of a leaf

I am trying to build a tree similar to this one : 1 / \ 2 3 /|\ 4 5 6 / 7 With that tree, I must be able to get all ancestors for each ...
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275 views

Wavefront-Reader (.obj) in Java - Part 1

I want to implement a wavefront-reader in Java. Therefore I've created some classes to extract a Vector3f and Vector2f (I use ...
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4k views

Hibernate and the Repository Pattern

I have already asked a question on stackoverflow on how to understand the Reporitory Pattern but I'm still having very big troubles in getting a good design implemented on my server. I'm desperately ...
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76 views

Advice on modelling with generics in Java

Use Case The third party library that I am working with implements its data model in this fashion. ...
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91 views

Minimum amount of edges that needs to be traversed to visit all vertices... or something like that

So I have this problem, where I'm given m connections over n vertices. The vertices are labeled ...
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0answers
614 views

Exception logger for servlets and JSPs

I hate using unnecessary catch blocks and I like to see my code look beautiful. In most of the cases in my project, which is a web application, I can't declare many ...
4
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1answer
111 views

Porting a web-based POS system to Android

I'm currently porting a web-based POS system to Android. The Android version uses NavigationDrawer to navigate between menus. What I need a code review on is my ...
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0answers
76 views

screen recording application

I'm developing a screen recording application using java. I've modified code from https://dzone.com/articles/screen-record-play-using-java where all the external jars required for this application are ...
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131 views

Exception handling: using @JsonProperty value to make error message

If the validation in RestController fails, I need to handle MethodArgumentNotValidException and provide an errorMessage, that ...
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0answers
69 views

How can I filter and sort LinkedList faster and more effective?I have list of orders that should be processed

I have method that fetches all orders from Database and filtering, sorting that data(I know better to do It by specific query to Database but I dont know how). I have Order entity that has following <...
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0answers
123 views

Android APP connect to FTP server in Java

I am attempting to build an Android APP with the ability to connect specified FTP server in Java. The connection operation has been performed in FTPconnection class ...
3
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1answer
97 views

Find all combinations of numbers of a set that add up to a given target - avoid for loops

I am thinking about the following problem: Consider a 3-numbers lock, i.e. a lock which has three little number wheels that opens whenever the sum of these three numbers equals 75. I know, this doesn'...
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62 views

Split an even length array in two such that each sub-arrays sum is as close as possible

I am currently iteratively forcing the solution by evaluating all of one elements possible coexisting elements for the closest combination to half of the initial arrays sum. Note: The initial array is ...
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92 views

Migrate customer and transaction data from CSV to MongoDB

I wrote a Java Spring Boot application with MongoDB that on every application start loads customer, account type and transaction details from CSV files to MongoDB. It has one end point that returns ...

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