设计模式之组合模式

作用

又叫部分整体模式，它创建了对象组的树形结构，将对象组合成树状结构以表示“整体-部分”的层次关系，Composite使得用户对单个对象和组合对象的使用具有一致性。

原理

Component：组合中对象的接口，适当情况下实现所有类共有方法的默认行为，用于管理和访问Component子部件，Component可以是抽象类或者接口。

Composite：非叶子节点，用于存储子部件，在Component接口中实现子部件的相关操作，比如增加、删除。

Leaf：在组合中表示叶子节点，叶子节点没有子节点。

案例

组织构件

public abstract class OrganizationComponent {

    private String name;
    private String desc;

    public OrganizationComponent(String name, String desc) {
        this.name = name;
        this.desc = desc;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDesc() {
        return desc;
    }

    public void setDesc(String desc) {
        this.desc = desc;
    }

    public void add(OrganizationComponent organizationComponent) {
        throw new UnsupportedOperationException();
    }

    public void remove(OrganizationComponent organizationComponent) {
        throw new UnsupportedOperationException();
    }

    public abstract void print();

}

大学

public class University extends OrganizationComponent {

    private List<OrganizationComponent> organizationComponents = new ArrayList<>();

    public University(String name, String desc) {
        super(name, desc);
    }

    @Override
    public void add(OrganizationComponent organizationComponent) {
        this.organizationComponents.add(organizationComponent);
    }

    @Override
    public void remove(OrganizationComponent organizationComponent) {
        this.organizationComponents.remove(organizationComponent);
    }

    @Override
    public void print() {
        System.out.println("----------" + getName() + "----------");
        organizationComponents.forEach(OrganizationComponent::print);
    }
}

学院

public class College extends OrganizationComponent {

    private List<OrganizationComponent> organizationComponents = new ArrayList<>();

    public College(String name, String desc) {
        super(name, desc);
    }

    @Override
    public void add(OrganizationComponent organizationComponent) {
        this.organizationComponents.add(organizationComponent);
    }

    @Override
    public void remove(OrganizationComponent organizationComponent) {
        this.organizationComponents.remove(organizationComponent);
    }

    @Override
    public void print() {
        System.out.println("----------" + getName() + "----------");
        organizationComponents.forEach(OrganizationComponent::print);
    }
}

院系

public class Department extends OrganizationComponent {

    public Department(String name, String desc) {
        super(name, desc);
    }

    @Override
    public void print() {
        System.out.println(getName());
    }
}

调用

public class Client {

    public static void main(String[] args) {
        University university = new University("加州大学洛杉矶分校", "UCLA");

        College softwareCollege = new College("软件学院", "Software College");
        College informationCollege = new College("信息学院", "Information College");

        university.add(softwareCollege);
        university.add(informationCollege);

        softwareCollege.add(new Department("软件工程","Software Engineering"));
        softwareCollege.add(new Department("网络工程","Network Engineering"));
        softwareCollege.add(new Department("计算机科学与技术","Computer Science and Technology"));

        informationCollege.add(new Department("通信工程", "Communications Engineering"));
        informationCollege.add(new Department("信息工程", "Information Engineering"));

        university.print();
    }

}

源码

Map：Component

HashMap：Composite

Node：Leaf

public interface Map<K,V> {
}

public class HashMap<K,V> extends AbstractMap<K,V> implements Map<K,V>, Cloneable, Serializable {
}

static class Node<K,V> implements Map.Entry<K,V> {
}