patterns8CompositePattern

1package pkg8patterns;2 3/*4 * Composite (Structural)5 * ----------------------6 * INTENT: compose objects into tree structures and treat individual objects and7 *         compositions uniformly.8 * UML: Component <|-- Leaf and <|-- Composite (Composite holds Component children).9 * PROS: uniform treatment of leaves and groups; easy recursive operations.10 * CONS: can make the design overly general.11 * REAL-WORLD: file systems, UI component trees, org charts.12 */13import java.util.*;14 15public class patterns8CompositePattern {16 17    interface FileSystemNode { int size(); String name(); }18 19    // Leaf20    static class FileLeaf implements FileSystemNode {21        private final String name; private final int size;22        FileLeaf(String name, int size) { this.name = name; this.size = size; }23        public int size() { return size; }24        public String name() { return name; }25    }26 27    // Composite28    static class Directory implements FileSystemNode {29        private final String name;30        private final List<FileSystemNode> children = new ArrayList<>();31        Directory(String name) { this.name = name; }32        Directory add(FileSystemNode n) { children.add(n); return this; }33        public int size() { return children.stream().mapToInt(FileSystemNode::size).sum(); }34        public String name() { return name; }35    }36 37    public static void main(String[] args) {38        Directory root = new Directory("root")39                .add(new FileLeaf("a.txt", 100))40                .add(new Directory("sub")41                        .add(new FileLeaf("b.txt", 200))42                        .add(new FileLeaf("c.txt", 300)));43        System.out.println("total size of '" + root.name() + "' = " + root.size() + " bytes");44    }45}