java设计模式之组合模式

设计模式种的组合模式不是类与类之间那个组合。

而是只业务逻辑种的那种树形数据结构，比如文件目录、公司的组织架构等。

这种模式在实际的项目开发中并不那么常用。但是，一旦数据满足树形结构，应用这种模式就能发挥很大的作用，能让代码变得非常简洁。

我们以文件目录为例，通过实现一个文件目录树来理解组合模式。

首先实现一个抽象目录类

public abstract class FileSystemNode {
    protected String path;

    public FileSystemNode(String path) {
        this.path = path;
    }

    public String getPath() {
        return path;
    }

    /**
     * 统计文件个数
     * @return
     */
    public abstract int countNumOfFiles();

    /**
     * 统计文件大小
     * @return
     */
    public abstract long countSizeOfFiles();

    /**
     * 遍历目录
     */
    public abstract void travel();
}

它有两个子类，分别是文件类和目录类，文件类代表目录中的一个文件

public class File extends FileSystemNode {

    public File(String path) {
        super(path);
    }

    @Override
    public int countNumOfFiles() {
        return 1;
    }

    @Override
    public long countSizeOfFiles() {
        java.io.File file = new java.io.File(path);
        if(!file.exists()){
            return 0;
        }
        return file.length();
    }

    @Override
    public void travel() {
        System.out.println(path);
    }
}

目录类下可以是一个或多个文件，也可能有几个目录。

public class Directory extends FileSystemNode {
    private List<FileSystemNode> subNodes = new ArrayList<>();

    public Directory(String path) {
        super(path);
    }

    @Override
    public int countNumOfFiles() {
        int numFiles = 0;
        for (FileSystemNode subNode : subNodes) {
            numFiles += subNode.countNumOfFiles();
        }
        return numFiles;
    }

    @Override
    public long countSizeOfFiles() {
        int fileSizes = 0;
        for (FileSystemNode subNode : subNodes) {
            fileSizes += subNode.countSizeOfFiles();
        }
        return fileSizes;
    }

    @Override
    public void travel() {
        for (FileSystemNode subNode : subNodes) {
            if(subNode instanceof File){
                System.out.println(subNode.getPath());
            }else if(subNode instanceof Directory){
                subNode.travel();
            }
        }
    }

    public void addSubNode(FileSystemNode fileOrDir) {
        subNodes.add(fileOrDir);
    }

    public void removeSubNode(FileSystemNode fileOrDir) {
        int size=subNodes.size();
        int curNode=Integer.MAX_VALUE;
        for(int i=0;i<size;i++){
            if(subNodes.get(i).getPath().equals(fileOrDir.getPath())){
                curNode=i;
                break;
            }
        }
        if(curNode<size){
            subNodes.remove(curNode);
        }
    }

}

入口类

public class Application {
    public static void main(String[] args) {
        String baseDir="/Users/gaochengcheng/Documents/gitlab/java-mine/data-structure/src/main/java/com/example/java/";
        Directory algorithm = new Directory(baseDir+"algorithm");
        Directory basic = new Directory(baseDir+"algorithm/basic");
        Directory other = new Directory(baseDir+"algorithm/other");

        File lru = new File(baseDir + "algorithm/basic/LRU.java");
        File heap = new File(baseDir + "algorithm/basic/MHeap.java");
        File hashmap = new File(baseDir + "algorithm/basic/MHashMap.java");
        basic.addSubNode(lru);
        basic.addSubNode(heap);
        basic.addSubNode(hashmap);

        File gcd = new File(baseDir + "algorithm/other/GCD.java");
        File matrix = new File(baseDir + "algorithm/other/MatrixBasic.java");
        File decompose = new File(baseDir + "algorithm/other/MatrixDecompose.java");
        other.addSubNode(gcd);
        other.addSubNode(matrix);
        other.addSubNode(decompose);

        algorithm.addSubNode(basic);
        algorithm.addSubNode(other);

        System.out.println(algorithm.countNumOfFiles());
        System.out.println(algorithm.countSizeOfFiles());
        algorithm.travel();
        
    }
}

输出：

6
12269
/Users/gaochengcheng/Documents/gitlab/java-mine/data-structure/src/main/java/com/example/java/algorithm/basic/LRU.java
/Users/gaochengcheng/Documents/gitlab/java-mine/data-structure/src/main/java/com/example/java/algorithm/basic/MHeap.java
/Users/gaochengcheng/Documents/gitlab/java-mine/data-structure/src/main/java/com/example/java/algorithm/basic/MHashMap.java
/Users/gaochengcheng/Documents/gitlab/java-mine/data-structure/src/main/java/com/example/java/algorithm/other/GCD.java
/Users/gaochengcheng/Documents/gitlab/java-mine/data-structure/src/main/java/com/example/java/algorithm/other/MatrixBasic.java
/Users/gaochengcheng/Documents/gitlab/java-mine/data-structure/src/main/java/com/example/java/algorithm/other/MatrixDecompose.java