设计模式基础篇-13-组合模式（Composite Pattern）

组合模式，将单个对象和组合对象按照完全一样的事物对待，其实就是将一类东西组合在一起，通过条件，选择性的输出；

举个列子： 一个公司旗下，有很多部门，比如it部门，hr部门，等，我现在想知道it部门有多人，这代码怎么写，这个时候使用组合模式就不错

public abstract class HeadQuarters {

    
    private String name;

    HeadQuarters(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public abstract void add(HeadQuarters headQuarters);

    public abstract HeadQuarters getChild(String orgName);

    public abstract int getStaffCount();

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

import java.util.ArrayList;
import java.util.List;


public class HeadQuartersImpl extends HeadQuarters {


    private List headQuarters = new ArrayList<>();

    HeadQuartersImpl(String name) {
        super(name);
    }

    @Override
    public void add(HeadQuarters headQuarters) {
        this.headQuarters.add(headQuarters);
    }

    @Override
    public HeadQuarters getChild(String orgName) {
        for (HeadQuarters org : headQuarters) {
            HeadQuarters targetOrg = org.getChild(orgName);
            if (targetOrg != null) {
                return targetOrg;
            }
        }
        return null;
    }

    @Override
    public int getStaffCount() {
        int count = 0;
        for (HeadQuarters headQuarters : this.headQuarters) {
            count += headQuarters.getStaffCount();
        }
        return count;
    }
}

public class ItDepartment extends HeadQuarters {

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

    
    @Override
    public int getStaffCount() {
        return 20;
    }

    @Override
    public void add(HeadQuarters headQuarters) {
        throw new UnsupportedOperationException(this.getName() + "已经是最基本部门，无法增加下属部门");
    }

    @Override
    public HeadQuarters getChild(String orgName) {
        if (getName().equals(orgName)) {
            return this;
        }
        return null;
    }
}

调用 listOrgInfo 即可

public class HeadQuartersClient {

    private HeadQuarters constructOrganization() {

        //构建总部
        HeadQuartersImpl head = new HeadQuartersImpl("总公司");
        ItDepartment headIt = new ItDepartment("总公司It部");
        head.add(headIt);

        //构建分公司
        HeadQuartersImpl branch1 = new HeadQuartersImpl("天津分公司");
        ItDepartment branch1It = new ItDepartment("天津分公司It部");
        branch1.add(branch1It);

        //将分公司加入到head中
        head.add(branch1);
        return head;
    }

    public void listOrgInfo() {
        HeadQuarters org = constructOrganization();
        System.out.println(String.format("%s共有%d名员工",
                org.getName(), org.getStaffCount()));

        HeadQuarters subOrg = org.getChild("天津分公司行政部");
        System.out.println(String.format("%s共有%d名员工",
                subOrg.getName(), subOrg.getStaffCount()));
    }
}