image-processing: Explain the adapter pattern

image-processing/index.md

@@ -73,6 +73,62 @@ The generic type `V` is used throughout the `graphs` package to represent the ve
 `Node`
 : An [**adapter**](https://en.wikipedia.org/wiki/Adapter_pattern) for the `Graph` interface that delegates responsibility for `neighbors` to each individual `Node` rather than the entire `Graph`.
 
+Without the `Node` interface, we would need to centralize all of the logic in the `Graph` implementation.
+
+```java
+public class ExampleGraph implements Graph<Node> {
+    public List<Node> neighbors(Node node) {
+        if (isSource(node)) {
+            return sourceNeighbors(node);
+        } else if (isSink(node)) {
+            return sinkNeighbors(node);
+        } else {
+            return pixelNeighbors(node);
+        }
+    }
+
+    private List<Node> sourceNeighbors(Node node) {
+        ...
+    }
+
+    private List<Node> sinkNeighbors(Node node) {
+        ...
+    }
+
+    private List<Node> pixelNeighbors(Node node) {
+        ...
+    }
+}
+```
+
+By introducing the `Node` interface, the logic for the graph is divided into separate implementations. This improves encapsulation by enabling each implementation to maintain its own fields and logic separate from other implementations.
+
+```java
+public class ExampleGraph implements Graph<Node> {
+    public List<Node> neighbors(Node node) {
+        return node.neighbors();
+    }
+}
+
+public class Source implements Node {
+    public List<Node> neighbors() {
+        ...
+    }
+}
+
+public class Sink implements Node {
+    public List<Node> neighbors() {
+        ...
+    }
+}
+
+public class Pixel implements Node {
+    public List<Node> neighbors() {
+        ...
+    }
+}
+```
+
 ### Reference implementation
 
 `AdjacencyListSeamFinder(DijkstraSolver::new)`