Enforce immutability via final and unmodifiableList.

src/main/org/insa/graph/Node.java

@@ -1,65 +1,73 @@
 package org.insa.graph;
 
 import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 
 public class Node implements Comparable<Node> {
 
-	// ID of the node.
-	private int id;
-	
-	// Point of this graph.
-	private Point point;
-	
-	// Successors.
-	private ArrayList<Arc> successors;
-	
-	/**
-	 * Create a new Node corresponding to the given Point with
-	 * an empty list of successors.
-	 * 
-	 * @param point
-	 */
-	public Node(int id, Point point) {
-		this.id = id;
-		this.point = point;
-		this.successors = new ArrayList<Arc>();
-	}
+    // ID of the node.
+    private final int id;
 
-	/**
-	 * Add a successor to this node.
-	 * 
-	 * @param arc Arc to the successor.
-	 */
-	protected void addSuccessor(Arc arc) {
-		successors.add(arc);
-	}
-	
-	/**
-	 * @return ID of this node.
-	 */
-	public int getId() { return id; }
-	
-	/**
-	 * @return List of successors of this node.
-	 */
-	public ArrayList<Arc> getSuccessors() { return successors; }
-	
-	/**
-	 * @return Point of this node.
-	 */
-	public Point getPoint() { return point; }
-	
-	@Override
-	public boolean equals(Object other) {
-		if (other instanceof Node) {
-			return getId() == ((Node) other).getId();
-		}
-		return false;
-	}
+    // Point of this graph.
+    private final Point point;
+
+    // Successors.
+    private final ArrayList<Arc> successors;
+
+    /**
+     * Create a new Node corresponding to the given Point with an empty list of
+     * successors.
+     * 
+     * @param point
+     */
+    public Node(int id, Point point) {
+        this.id = id;
+        this.point = point;
+        this.successors = new ArrayList<Arc>();
+    }
+
+    /**
+     * Add a successor to this node.
+     * 
+     * @param arc Arc to the successor.
+     */
+    protected void addSuccessor(Arc arc) {
+        successors.add(arc);
+    }
+
+    /**
+     * @return ID of this node.
+     */
+    public int getId() {
+        return id;
+    }
+
+    /**
+     * @return List of successors of this node.
+     */
+    public List<Arc> getSuccessors() {
+        return Collections.unmodifiableList(successors);
+    }
+
+    /**
+     * @return Point of this node.
+     */
+    public Point getPoint() {
+        return point;
+    }
+
+    @Override
+    public boolean equals(Object other) {
+        if (other instanceof Node) {
+            return getId() == ((Node) other).getId();
+        }
+        return false;
+    }
+
+    @Override
+    public int compareTo(Node other) {
+        return Integer.compare(getId(), other.getId());
+    }
 
-	@Override
-	public int compareTo(Node other) {
-		return Integer.compare(getId(), other.getId());
-	}
-	
 }