Composite Pattern

Composite is about dealing the whole and the part in a uniform way. It's useful in building tree like structures and then working on them in a uniform way. Let's see how to implement one related to a tree.

The Node interface

public interface Node {

public void process();

}

The whole

public class NonLeafNode implements Node {

private final List<Node> nodeList = new ArrayList<Node>();

public void addNode(Node node) {

nodeList.add(node);

}

@Override

public void process() {

System.out.println("I am not a leaf node");

for (Node node : nodeList) {

node.process();

}

}

}

The part

public class Leaf implements Node {

@Override

public void process() {

System.out.println("I am leaf");

}

}

And the main method

public class Composite {

public static void main(String[] args) {

NonLeafNode root = new NonLeafNode();

NonLeafNode level1 = new NonLeafNode();

root.addNode(level1);

Leaf leaf = new Leaf();

level1.addNode(leaf);

root.process();

}

}

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