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GJ is a programming language that was developed as an extension to the Java programming language to support generic types. It was developed by Martin Odersky, Philip Wadler, and Gilad Bracha. GJ stands for "Generic Java" and it was designed to be backwards-compatible with existing Java code. This means that any legal Java program is also a legal GJ program that has the same meaning. In 2004, the features of GJ were incorporated into the official Java language specification, starting from Java version 5.0. Hence, GJ is now considered a part of the standard Java language.

Ask the right questions secure the right GJ talent among an increasingly shrinking pool of talent.

First 20 minutes

General GJ app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in GJ application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

How would you describe the basic structure of a GJ file?

A GJ file is structured as a collection of features, where each feature is a combination of a geometry object and additional properties. The geometry object describes the spatial characteristics of the feature, while the properties contain other descriptive or attribute data.

What are the different types of geometries supported in GJ?

GJ supports several types of geometries, including Point, MultiPoint, LineString, MultiLineString, Polygon, MultiPolygon, and GeometryCollection.

Describe the difference between a Point and a MultiPoint in GJ.

A Point is a single coordinate pair, while a MultiPoint is a collection of Points. In other words, a Point represents a single location in space, while a MultiPoint represents multiple locations.

How would you convert a shapefile to GJ?

You can use a tool like ogr2ogr from the GDAL library to convert a shapefile to GJ. The basic command would look something like 'ogr2ogr -f GJ output.gj input.shp'.

What are the benefits of using GJ over other geospatial data formats?

GJ is a lightweight, flexible, and human-readable format. It is based on JSON, which makes it easy to work with in many programming languages. It also supports a wide range of geometric types and allows for the inclusion of additional properties with each feature.

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What you’re looking for early on

Does the candidate have a strong understanding of GJ development?

How well does the candidate communicate?

Is the candidate able to solve problems effectively?

Does the candidate show a willingness to learn and adapt?

Next 20 minutes

Specific GJ development questions

The next 20 minutes of the interview should focus on the candidate's expertise with specific backend frameworks, their understanding of RESTful APIs, and their experience in handling data storage and retrieval efficiently.

How would you validate a GJ file?

You can use a tool like geojsonlint to validate a GJ file. This tool checks the file against the GJ specification and returns any errors or warnings.

Describe the difference between a LineString and a Polygon in GJ.

A LineString is a sequence of points that forms a line. A Polygon, on the other hand, is a sequence of points that forms a closed ring. In other words, a LineString represents a path, while a Polygon represents an area.

What are the limitations of GJ?

While GJ is a powerful tool, it does have some limitations. For example, it does not support curves or other complex geometries. It also does not have built-in support for spatial operations like intersection or union.

How would you handle large GJ files?

For large GJ files, it may be necessary to use a streaming approach to process the data incrementally rather than loading the entire file into memory. Libraries like GeoJSON-Stream can facilitate this.

Describe the difference between a MultiPolygon and a GeometryCollection in GJ.

A MultiPolygon is a collection of Polygons, while a GeometryCollection is a collection of any type of geometries. In other words, a MultiPolygon contains multiple areas, while a GeometryCollection can contain a mix of points, lines, and areas.

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At this point, a skilled GJ engineer should demonstrate strong problem-solving abilities, proficiency in GJ programming language, and knowledge of software development methodologies. Red flags include lack of hands-on experience, inability to articulate complex concepts, or unfamiliarity with standard coding practices.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with GJ.

What does the following code do?
public class HelloWorld { public static void main(String[] args) { System.out.println("Hello, World!"); } }
This code prints the string 'Hello, World!' to the console.
What will be the output of the following code?
public class Test { public static void main(String[] args) { int x = 10; int y = 5; System.out.println(x + y); } }
The output of the code will be 15. It adds the values of x and y and prints the result.
What does the following code do?
import java.util.Arrays; public class Test { public static void main(String[] args) { int[] array = {1, 2, 3, 4, 5}; Arrays.sort(array); System.out.println(Arrays.toString(array)); } }
This code sorts an array of integers in ascending order and then prints the sorted array.
What does the following code do?
public class Test { public static void main(String[] args) { Thread thread = new Thread(() -> { System.out.println("New thread created."); }); thread.start(); } }
This code creates a new thread and starts it. The new thread prints 'New thread created.' to the console.

Wrap-up questions

Final candidate for GJ Developer role questions

The final few questions should evaluate the candidate's teamwork, communication, and problem-solving skills. Additionally, assess their knowledge of microservices architecture, serverless computing, and how they handle GJ application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

What are the use cases for GJ?

GJ is used in a wide range of applications, including mapping, geospatial analysis, data visualization, and more. It is particularly popular in web-based applications due to its compatibility with JSON.

How would you perform spatial operations on GJ data?

You can use a library like Turf.js to perform spatial operations on GJ data. This includes operations like buffer, intersect, union, and more.

What are the considerations when indexing GJ data?

When indexing GJ data, it's important to consider the type of queries that will be performed. For example, if you will be performing a lot of spatial queries, a spatial index like a R-tree may be appropriate.

GJ application related

Product Perfect's GJ development capabilities

Beyond hiring for your GJ engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in GJ projects, and can engage in multiple capacities.

GJ Consultive assessments

GJ Application Conversion Assessment GJ Application Integration Assessment GJ Data & Database Integration Assessment

Custom GJ development projects

Custom GJ App Conversion GJ Custom App Development Process App UI Design for GJ Facelifts

Hiring guide for GJ Engineers

GJ Developer Hiring Guide

What you’re looking for early on

The ideal back-end app developer

What you’re looking to see on the GJ engineer at this point.

GJ Consultive assessments

Custom GJ development projects