BFS Visualization in Java

A Java project for visualizing the Breadth-First Search (BFS) algorithm step by step.

The application reads a graph definition from a .txt file, runs BFS, and displays the search process visually using JavaFX.

Features

• step-by-step BFS visualization
• highlights node expansion and traversal order
• multiple example input files
• reconstructs and displays the final path
• accepts comments and flexible spacing in input files

Video

A short video demonstration of the project: https://youtu.be/VT-ZhxdzErE

How BFS Works in This Project

This visualizer demonstrates Breadth-First Search, which explores nodes level by level.

Important note:

• BFS finds the path with the fewest steps / edges
• during BFS, each expansion step is treated uniformly; BFS ignores edge weights while choosing which node to expand next
• the displayed total path cost is determined afterwards from the costs defined in the input file

Running the Project

Run the project with:

mvn clean javafx:run -Djavafx.args="--ssf src/main/resources/intro.txt"

Other example files:

mvn clean javafx:run -Djavafx.args="--ssf src/main/resources/simple_ex.txt"
mvn clean javafx:run -Djavafx.args="--ssf src/main/resources/1_to_9.txt"
mvn clean javafx:run -Djavafx.args="--ssf src/main/resources/greek_alphabet.txt"
mvn clean javafx:run -Djavafx.args="--ssf src/main/resources/california.txt"
mvn clean javafx:run -Djavafx.args="--ssf src/main/resources/21_nodes.txt"
mvn clean javafx:run -Djavafx.args="--ssf src/main/resources/100_nodes.txt"

Input Format

The graph is provided through a .txt file.

Structure

• First line — start state
• Second line — one or more goal states
• Remaining lines — transitions for each state

Transition format

state: next_state1,cost1 next_state2,cost2

Example:

A
G
A: B,1 C,2
B: D,3 E,1
C: F,2 G,4

Input Rules

• extra spaces are tolerated
• comments can be added with #
• each transition line must start with a state name followed by :
• each successor must include both a state name and a cost

Included Example Files

The project includes several example inputs in src/main/resources:

• intro.txt
• simple_ex.txt
• 1_to_9.txt
• greek_alphabet.txt
• california.txt
• 21_nodes.txt
• 100_nodes.txt

Project Structure

Node.java

Represents one node in the search.

Stores:

• state — node name
• cost — cost from the parent node
• depth — level in the search tree
• parent — node from which this node was reached

BFS.java

Contains the main BFS logic.

Uses:

• stateSpace — graph built from the input file
• open — queue of discovered nodes waiting to be processed
• tree — expanded nodes
• path — final reconstructed path from the start state to the goal state
• visitedStates — prevents revisiting nodes
• bfsEvents — events used for visualization

BFSEvent.java

Represents one event in the BFS animation.

EventStates.java

Defines all possible event types used by the visualizer.

BFSVisualizer.java

Contains the graphical animation logic and displays the BFS process step by step.

Additional Notes

• In open, nodes are ordered by value and then alphabetically.
• BFS itself expands nodes by level.
• The final displayed path cost is calculated from the edge costs defined in the input file.