MPI4.1文档 -- 阻塞接收与其状态处理-CFANZ编程社区

组合模式的典型例子通常涉及到树形结构的处理，下面是几个形象且易于理解的例子：

文件系统

在文件系统中，目录可以包含文件或者其他目录，但是从用户的角度来看，目录和文件都可以被“打开”或者“获取大小”。这里的目录就是一个组合对象，文件是叶子节点。

interface FileSystemItem {
    void showProperties();
    long getSize();
}

class File implements FileSystemItem {
    private String name;
    private long size;

    public File(String name, long size) {
        this.name = name;
        this.size = size;
    }

    @Override
    public void showProperties() {
        System.out.println("File: " + name + " (Size: " + size + ")");
    }

    @Override
    public long getSize() {
        return size;
    }
}

class Directory implements FileSystemItem {
    private String name;
    private List<FileSystemItem> children = new ArrayList<>();

    public Directory(String name) {
        this.name = name;
    }

    public void add(FileSystemItem item) {
        children.add(item);
    }

    @Override
    public void showProperties() {
        System.out.println("Directory: " + name);
        for (FileSystemItem child : children) {
            child.showProperties();
        }
    }

    @Override
    public long getSize() {
        long size = 0;
        for (FileSystemItem child : children) {
            size += child.getSize();
        }
        return size;
    }
}

图形界面组件

在图形用户界面（GUI）中，容器组件可以包含其他容器组件或者叶子组件（如按钮、文本框等）。无论是容器还是叶子组件，都可以对它们执行某些操作，如绘制、启用/禁用等。

interface GUIComponent {
    void render();
}

class Button implements GUIComponent {
    @Override
    public void render() {
        System.out.println("Render Button");
    }
}

class Panel implements GUIComponent {
    private List<GUIComponent> children = new ArrayList<>();

    public void add(GUIComponent component) {
        children.add(component);
    }

    @Override
    public void render() {
        System.out.println("Render Panel");
        for (GUIComponent child : children) {
            child.render();
        }
    }
}

组织结构

在组织结构中，公司可以分为部门，部门下可以有子部门或员工。部门和员工都可以执行某些操作，如获取成本。

interface OrganizationComponent {
    void printStructure();
    double getCost();
}

class Employee implements OrganizationComponent {
    private String name;
    private double salary;

    public Employee(String name, double salary) {
        this.name = name;
        this.salary = salary;
    }

    @Override
    public void printStructure() {
        System.out.println("Employee: " + name + ", Salary: " + salary);
    }

    @Override
    public double getCost() {
        return salary;
    }
}

class Department implements OrganizationComponent {
    private String name;
    private List<OrganizationComponent> members = new ArrayList<>();

    public Department(String name) {
        this.name = name;
    }

    public void add(OrganizationComponent component) {
        members.add(component);
    }

    @Override
    public void printStructure() {
        System.out.println("Department: " + name);
        for (OrganizationComponent member : members) {
            member.printStructure();
        }
    }

    @Override
    public double getCost() {
        double cost = 0;
        for (OrganizationComponent member : members) {
            cost += member.getCost();
        }
        return cost;
    }
}