什么是组合模式。用java代码写一个案例

组合模式是一种结构型设计模式，它允许将对象组合成树形结构来表示“部分-整体”的层次结构。组合模式使得用户可以像对待单个对象一样对待整个组合对象。

以下是一个使用组合模式的简单示例，它表示了一个组织结构，包括公司、部门和员工。每个公司可以包含多个部门，每个部门可以包含多个员工。

interface OrganizationUnit {
    void print();
}

class Company implements OrganizationUnit {
    private List<OrganizationUnit> departments = new ArrayList<>();

    public void addDepartment(OrganizationUnit department) {
        departments.add(department);
    }

    @Override
    public void print() {
        System.out.println("Company");
        for (OrganizationUnit unit : departments) {
            unit.print();
        }
    }
}

class Department implements OrganizationUnit {
    private List<OrganizationUnit> employees = new ArrayList<>();

    public void addEmployee(OrganizationUnit employee) {
        employees.add(employee);
    }

    @Override
    public void print() {
        System.out.println("Department");
        for (OrganizationUnit unit : employees) {
            unit.print();
        }
    }
}

class Employee implements OrganizationUnit {
    private String name;

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

    @Override
    public void print() {
        System.out.println("Employee: " + name);
    }
}

public class CompositePatternExample {
    public static void main(String[] args) {
        Company company = new Company();

        Department department1 = new Department();
        department1.addEmployee(new Employee("John"));
        department1.addEmployee(new Employee("Jane"));

        Department department2 = new Department();
        department2.addEmployee(new Employee("Bob"));
        department2.addEmployee(new Employee("Alice"));

        company.addDepartment(department1);
        company.addDepartment(department2);

        company.print();
    }
}

输出：

Company
Department
Employee: John
Employee: Jane
Department
Employee: Bob
Employee: Alice