一、概念
- 组合模式(Composite Pattern):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
- 组合模式依据树形结构来组合对象,用来表示部分以及整体层次
- 组合模式使得用户单个对象和组合对象的访问具有一致性,即组合能让客户以一致的方式处理个别对象以及组合对象
- 简化客户端操作,客户端只需要面对一致的对象而不用考虑整体部分或叶子节点问题
- 具有较强的拓展性,当我们要更改组合对象时,我们只需要调整内部的层次关系,客户端不用做出任何改动
- 方便创建出复杂的层次结构,客户端不用理会组合里面的组成细节,容易添加节点或叶子从而创建出复杂的树形结构
- 需要遍历组织机构、或者处理的对象具有树形结构时,非常适合使用组合模式
- 要求较高的抽象性,如果叶子和节点有很大差异性的话,不适合使用组合模式
- 组合模式的角色及职责:
- Component:这是组合中对象声明接口,在适当情况下,实现所有类共有的接口默认行为,用于访问和管理Component子部件,Component可以是抽象类或者接口
- Leaf:在组合中表示叶子节点,叶子节点没有 子节点
- Composite:非叶子节点,用于存储子部件,在Component实现子部件的相关操作,比如增加(add),删除
二、组合模式解决学校院系展示的应用实例
public abstract class OrganizationComponent {
private String name;
private String desc;
public OrganizationComponent() {
}
public OrganizationComponent(String name, String desc) {
this.name = name;
this.desc = desc;
}
public abstract void add(OrganizationComponent organizationComponent);
public abstract void remove(OrganizationComponent organizationComponent);
public abstract void print();
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 class School extends OrganizationComponent {
List<OrganizationComponent> colleges = new ArrayList<>();
public School() {
}
public School(String name, String desc) {
super(name, desc);
}
@Override
public void add(OrganizationComponent organizationComponent) {
colleges.add(organizationComponent);
}
@Override
public void remove(OrganizationComponent organizationComponent) {
colleges.remove(organizationComponent);
}
@Override
public void print() {
System.out.println(super.getName() + " " + super.getDesc());
for (OrganizationComponent college : colleges) {
college.print();
}
}
}
public class College extends OrganizationComponent {
List<OrganizationComponent> departments = new ArrayList<>();
public College() {
}
public College(String name, String desc) {
super(name, desc);
}
@Override
public void add(OrganizationComponent department) {
departments.add(department);
}
@Override
public void remove(OrganizationComponent department) {
departments.remove(department);
}
@Override
public void print() {
System.out.println(super.getName() + " " + super.getDesc());
for (OrganizationComponent department : departments) {
department.print();
}
}
}
public class Department extends OrganizationComponent {
public Department() {
}
public Department(String name, String desc) {
super(name, desc);
}
@Override
public void add(OrganizationComponent organizationComponent) {
throw new UnsupportedOperationException();
}
@Override
public void remove(OrganizationComponent organizationComponent) {
throw new UnsupportedOperationException();
}
@Override
public void print() {
System.out.println(super.getName() + " " + super.getDesc());
}
}