对组合模式的理解

2024-04-21 09:10:02
开发
38

一、场景

设计模式很依赖场景，通过场景也能更好理解这种模式解决了什么问题。

无论是学校还是公司，都存在组织结构。而且，这种结构多半是树状结构。
当类与类之间的结构也需要表达成树状结构时，组合模式就来大显身手了。

1、题目描述【案例来源】

小明所在的公司内部有多个部门，每个部门下可能有不同的子部门或者员工。
请你设计一个组合模式来管理这些部门和员工，实现对公司组织结构的统一操作。部门和员工都具有一个通用的接口，可以获取他们的名称以及展示公司组织结构。

2、输入描述

第一行是一个整数 N（1 <= N <= 100），表示后面有 N 行输入。
接下来的 N 行，每行描述一个部门或员工的信息。部门的信息格式为 D 部门名称，员工的信息格式为 E 员工名称，其中 D 或 E 表示部门或员工。

3、输出描述

输出公司的组织结构，展示每个部门下的子部门和员工

4、输入示例

MyCompany
8
D HR
E HRManager
D Finance
E AccountantA
E AccountantB
D IT
E DeveloperA
E DeveloperB

5、输出示例

Company Structure:
MyCompany
HR
HRManager
Finance
AccountantA
AccountantB
IT
DeveloperA
DeveloperB

二、实现（假的组合模式）

1、代码

public interface Component {
    String showName();
}

public class Company implements Component {
    private final String name;

    @Setter
    private List<Department> departments;

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

    public void addDepartment(Department department) {
        if (CollectionUtils.isEmpty(departments)) {
            departments = new ArrayList<>();
            departments.add(department);

        } else {
            departments.add(department);
        }
    }

    @Nullable
    public Department gotLastDepartment() {
        if (CollectionUtils.isEmpty(departments)) {
            return null;
        } else {
            return departments.get(departments.size() - 1);
        }
    }

    @Override
    public String showName() {
        return name;
    }

    public String showCompanyStructure() {
        StringBuilder sb = new StringBuilder("Company Structure:\n").append(showName()).append("\n");

        Optional.ofNullable(departments).ifPresent(departments -> departments.stream().filter(Objects::nonNull).forEach(department -> {
            sb.append("  ").append(department.showName()).append("\n");
            Optional.ofNullable(department.getEmployees()).ifPresent(employees -> {
                employees.stream().forEach(
                        employee -> sb.append("    ").append(employee.showName()).append("\n")
                );
            });
        }));

        return sb.toString();
    }
}

@Data
public class Department implements Component {
    private String name;
    private List<Employee> employees;

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

    @Override
    public String showName() {
        return this.name;
    }

    public void addEmployee(Employee employee) {
        if (CollectionUtils.isEmpty(employees)) {
            employees = new ArrayList<>();
            employees.add(employee);
        } else {
            employees.add(employee);
        }
    }
}

@AllArgsConstructor
public class Employee implements Component {
    private String name;

    @Override
    public String showName() {
        return name;
    }
}

public class Application {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String companyName = scanner.nextLine();
        Company company = new Company(companyName);
        int n = scanner.nextInt();
        for (int i = 0; i < n; i++) {
            String type = scanner.next();
            String name = scanner.next();

            if (StringUtils.equals(type, "D")) {
                company.addDepartment(new Department(name));
            } else if (StringUtils.equals(type, "E")) {
                Department department = company.gotLastDepartment();
                department.addEmployee(new Employee(name));
            }
        }
        System.out.printf(company.showCompanyStructure());
    }
}

2、为什么上面的写法是假的组合模式？

场景中的公司结构：
- 对这个结构进行建模，不应该是：

public class Company implements Component {
    private final String name;

    @Setter
    private List<Department> departments;
}

public class Department implements Component {
    private String name;
    private List<Employee> employees;
}

public class Employee implements Component {
    private String name;
}

因为上图实际上有2个基本结构：

// Company-Department (1 对 n)、Department-Employee（1对n）
class Composite implements Component {
	private String name;
	private List<Component> children;
}

// 这个便是Employee
class Leaf implements Component {
	private String name;
}

所以，没有Get到这一点，就容易写出假的组合模式。（写的时候也会发现写的很累）

三、实现（真的组合模式）

1、案例来源的实现

场景中题目的提供方，也给出了相应的实现：

public interface Component {
    void display(int depth);
}

public class Department implements Component {
    private String name;
    private List<Component> children;

    public Department(String name) {
        this.name = name;
        this.children = new ArrayList<>();
    }

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

    @Override
    public void display(int depth) {
        StringBuilder indent = new StringBuilder();
        for (int i = 0; i < depth; i++) {
            indent.append("  ");
        }

        System.out.println(indent + name);
        for (Component component : children) {
            component.display(depth + 1);
        }
    }
}

public class Employee implements Component {
    private String name;

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

    @Override
    public void display(int depth) {
        StringBuilder indent = new StringBuilder();
        for (int i = 0; i < depth; i++) {
            indent.append("  ");
        }
        System.out.println(indent + "  " + name);
    }
}

public class Company {
    private String name;
    private Department root;

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

    public void add(Component component) {
        root.add(component);
    }

    public void display() {
        System.out.println("Company Structure:");
        root.display(0); // 从 1 开始，以适配指定的缩进格式
    }


public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
// 读取公司名称
        String companyName = scanner.nextLine();
        Company company = new Company(companyName);
// 读取部⻔和员工数量
        int n = scanner.nextInt();
        scanner.nextLine(); // 消耗换行符
// 读取部⻔和员工信息
        for (int i = 0; i < n; i++) {
            String type = scanner.next();
            String name = scanner.nextLine().trim();
            if ("D".equals(type)) {

                Department department = new Department(name);
                company.add(department);
            } else if ("E".equals(type)) {
                Employee employee = new Employee(name);
                company.add(employee);
            }
        }
// 输出公司组织结构
        company.display();
    }
}

debug会发现，这并没有正确表示company的结构：
那为啥能输出这样的结果呢？

MyCompany
  HR
    HRManager
  Finance
    AccountantA
    AccountantB
  IT
    DeveloperA
    DeveloperB

原因在于：

public class Employee implements Component {
    ...

    @Override
    public void display(int depth) {
        StringBuilder indent = new StringBuilder();
        for (int i = 0; i < depth; i++) {
            indent.append("  ");
        }
        System.out.println(indent + "  " + name); // 这里的depth实际上是1，因此作者多加了"  "
    }
}

显然，这并不是正确的实现。

2、我的实现

public interface Component {
    void showName(int depth);
}

public class Composite implements Component {
    private String name;
    private List<Component> children;

    public Composite(String name) {
        this.name = name;
        children = new ArrayList<>();
    }

    public void addComponent(Component component) {
        children.add(component);
    }

    public Composite gotLastComposite() {
        if (!children.isEmpty()) {
            Component component = children.get(children.size() - 1);
            if (component instanceof Composite) {
                return (Composite) component;
            } else {
                throw new RuntimeException("last component is not composite");
            }

        } else {
            throw new RuntimeException("doesn't exist last component");
        }
    }

    @Override
    public void showName(int depth) {
        System.out.println(StringUtils.repeat("  ", depth) + name);
        for (Component child : children) {
            child.showName(depth + 1);
        }
    }
}

@AllArgsConstructor
public class Employee implements Component {
    private String name;

    @Override
    public void showName(int depth) {
        System.out.println(StringUtils.repeat("  ", depth) + name);
    }
}

public class Company extends Composite {

    public Company(String name) {
        super(name);
    }

    @Override
    public void showName(int depth) {
        System.out.println("Company Structure:");
        super.showName(depth);
    }
}

public class Application {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String companyName = scanner.nextLine();
        Company company = new Company(companyName);

        int n = scanner.nextInt();
        for (int i = 0; i < n; i++) {
            String type = scanner.next();
            String name = scanner.next();

            if (StringUtils.equals(type, "D")) {
                company.addComponent(new Composite(name));
            } else if (StringUtils.equals(type, "E")) {
                Composite department = company.gotLastComposite();
                department.addComponent(new Employee(name));
            }
        }

        company.showName(0);
    }
}

Company的结构：

四、个人思考

对真实场景建模后，类呈现树状结构，那么可以尝试使用组合模式设计代码：

class Composite implements Component {
	private String name;
	private List<Component> children;
}

// 这个便是Employee
class Leaf implements Component {
	private String name;
}

组合模式：实现接口A + 组合多个接口A

装饰模式、桥接模式都用到了组合的理念，但都是一对一的形式：
装饰模式：实现接口A + 组合接口A

public class EncryptDataSourceImpl implements DataSource {
    private DataSource dataSource;
}

桥接模式：实现接口A + 组合接口B

public class Circle implements Shape {
    private Color color;
}

原文地址:https://blog.csdn.net/weixin_37477009/article/details/137892511 本文来自互联网用户投稿，该文观点仅代表作者本人，不代表本站立场。本站仅提供信息存储空间服务，不拥有所有权，不承担相关法律责任。如若转载，请注明出处：https://www.suanlizi.com/kf/1781852860401717248.html 如若内容造成侵权/违法违规/事实不符，请联系《酸梨子》网邮箱：1419361763@qq.com进行投诉反馈，一经查实，立即删除！

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