Graph Display

The graph display utility renders directed acyclic graph (DAG) data as formatted text in the terminal. Unlike the Tree Display where each node has one parent, a DAG allows nodes to have multiple parents (fan-in). Shared dependencies are shown once rather than duplicated, making it ideal for visualizing build pipelines, dependency graphs, and task workflows.

Quick Start

import org.aesh.util.graph.Graph;
import org.aesh.util.graph.GraphNode;

GraphNode shared = GraphNode.of("C");
GraphNode root = GraphNode.of("Root")
        .child(GraphNode.of("A").child(shared))
        .child(GraphNode.of("B").child(shared));

String output = Graph.render(root);
invocation.println(output);

Output (diamond pattern — C is shared between A and B):

Root
┌─┴┐
A  B
└┬─┘
 C

GraphNode API

GraphNode provides a fluent API for building graph structures. The DAG semantics come from sharing the same node instance across multiple parents:

GraphNode shared = GraphNode.of("shared");
GraphNode root = GraphNode.of("root")
        .child(GraphNode.of("left").child(shared))
        .child(GraphNode.of("right").child(shared));

Method	Returns	Description
`GraphNode.of(label)`	`GraphNode`	Creates a new node
`child(GraphNode)`	`this`	Adds an existing node as child
`child(String)`	`this`	Creates and adds a leaf node
`label()`	`String`	Returns the node’s label
`children()`	`List`	Returns unmodifiable children list

Static API

For quick rendering of GraphNode graphs:

// Default UNICODE style
String output = Graph.render(root);

// Custom style
String output = Graph.render(root, GraphStyle.ASCII);

Builder API

For rendering existing typed DAGs without converting to GraphNode:

import org.aesh.util.graph.Graph;
import org.aesh.util.graph.GraphStyle;

String output = Graph.<Task>builder()
        .label(Task::getName)
        .children(Task::getDependencies)
        .style(GraphStyle.UNICODE)
        .build()
        .render(rootTask);

Method	Default	Description
`label(Function<T, String>)`	required	Extracts display text from each node
`children(Function<T, List<T>>)`	required	Extracts children (null/empty = leaf)
`style(GraphStyle)`	`UNICODE`	Visual style for connectors

Calling build() throws IllegalStateException if label or children are not set.

Graph Styles

Three predefined styles are available via GraphStyle:

UNICODE (default):

Root
┌─┴┐
A  B
└┬─┘
 C

ASCII:

Root
+-++
A  B
++-+
 C

ROUNDED:

Root
╭─┴╮
A  B
╰┬─╯
 C

Each style defines eleven box-drawing characters used for edge routing:

Character	UNICODE	ASCII	ROUNDED	Purpose
horizontal	`─`	`-`	`─`	Horizontal edge
vertical	`│`	`\|`	`│`	Vertical edge
downTee	`┬`	`+`	`┬`	Parent splits down
upTee	`┴`	`+`	`┴`	Child joins up
cross	`┼`	`+`	`┼`	Vertical crosses horizontal
topLeft	`┌`	`+`	`╭`	Corner: down+right
topRight	`┐`	`+`	`╮`	Corner: down+left
bottomLeft	`└`	`+`	`╰`	Corner: up+right
bottomRight	`┘`	`+`	`╯`	Corner: up+left
rightTee	`├`	`+`	`├`	T-junction: up+down+right
leftTee	`┤`	`+`	`┤`	T-junction: up+down+left

Common Patterns

Fan-out (one parent, multiple children)

GraphNode root = GraphNode.of("Root")
        .child("A")
        .child("B")
        .child("C");

 Root
┌──┼──┐
A  B  C

Diamond (shared dependency)

GraphNode shared = GraphNode.of("C");
GraphNode root = GraphNode.of("Root")
        .child(GraphNode.of("A").child(shared))
        .child(GraphNode.of("B").child(shared));

Root
┌─┴┐
A  B
└┬─┘
 C

Complex DAG (multiple shared nodes)

GraphNode d = GraphNode.of("D");
GraphNode a = GraphNode.of("A").child("C").child(d);
GraphNode b = GraphNode.of("B").child(d).child("E");
GraphNode root = GraphNode.of("Root").child(a).child(b);

 Root
 ┌─┴┐
 A  B
┌┴─┐│
│  ├┴─┐
C  D  E

Here D is shared between A and B — it appears once with edges from both parents. Each parent’s edges are drawn on separate routing rows to avoid visual ambiguity.

Using in Commands

Here is a complete command example that displays a build dependency graph:

@CommandDefinition(name = "deps", description = "Display dependency graph")
public class DepsCommand implements Command<CommandInvocation> {

    @Option(name = "style", shortName = 's', defaultValue = {"UNICODE"},
            description = "Graph style: ASCII, UNICODE, ROUNDED")
    private GraphStyle style;

    @Override
    public CommandResult execute(CommandInvocation invocation) {
        // Build a dependency graph
        GraphNode test = GraphNode.of("test");
        GraphNode compile = GraphNode.of("compile");
        GraphNode lint = GraphNode.of("lint");
        GraphNode validate = GraphNode.of("validate").child(compile).child(lint);
        GraphNode root = GraphNode.of("build")
                .child(validate)
                .child(test);

        String output = Graph.render(root, style);
        invocation.println(output);
        return CommandResult.SUCCESS;
    }
}

Cycle Detection

Graphs must be acyclic. If the graph contains a cycle, render() throws an IllegalArgumentException:

GraphNode a = GraphNode.of("A");
GraphNode b = GraphNode.of("B").child(a);
a.child(b); // creates A → B → A cycle

Graph.render(a); // throws IllegalArgumentException: "Graph contains a cycle"

Edge Cases

Scenario	Behavior
Root with no children	Only the root label is printed
`children()` returns `null`	Treated as a leaf node (no crash)
`children()` returns empty list	Treated as a leaf node
Cyclic graph	Throws `IllegalArgumentException`
Shared child node	Rendered once with edges from all parents

Tree vs Graph

Feature	Tree	Graph
Structure	Each node has one parent	Nodes can have many parents
Rendering	Vertical with indentation	Layered horizontal layout
Shared nodes	Duplicated in output	Shown once with fan-in
Cycle detection	N/A (tree structure)	Throws on cycles
Use case	File trees, hierarchies	Dependencies, pipelines

Use Tree for simple hierarchies (file systems, org charts). Use Graph when nodes can be shared across multiple parents (build steps, dependency resolution).

API Reference

GraphNode

Method	Returns	Description
`of(String)`	`GraphNode`	Factory method
`child(GraphNode)`	`GraphNode`	Add child node, returns this
`child(String)`	`GraphNode`	Add leaf child, returns this
`label()`	`String`	Get label
`children()`	`List`	Unmodifiable children list

Graph (static)

Method	Returns	Description
`render(GraphNode)`	`String`	Render with UNICODE style
`render(GraphNode, GraphStyle)`	`String`	Render with specified style
`builder()`	`Builder`	Create a generic builder

GraphStyle

Constant	Description
`ASCII`	Uses `+`, `-`, `\|` characters
`UNICODE`	Uses box-drawing characters (default)
`ROUNDED`	Uses rounded corners (`╭`, `╮`, `╰`, `╯`)