A mode defines a
composition mode: the objects are combined into a tree structure to represent a "part-to-whole" hierarchy, and the composition mode enables users to use a single object and a composite object with consistency.
Two Combination Patterns Example
1 Pattern Analysis
We use the company organizational chart to illustrate this pattern.
After analysis, we get the static class diagram of this mode as follows: 
2 Code example
2.1 Establish employee abstract class
package com.demo.composite;
/**
* Worker interface
*
* @author
*
*/
public abstract class Staff {
// employee ID
protected String no;
// employee name
protected String name;
// Position
protected String position;
// salary
protected float salary;
// private property length string
private int length;
// Construction method
public Staff(String no, String name, String position, float salary) {
this.no = no;
this.name = name;
this.position = position;
this.salary = salary;
// Calculate the total length in bytes
this.length += (no == null || "".equals(no.trim())) ? 0
: no.getBytes().length;
this.length += (name == null || "".equals(name.trim())) ? 0 : name
.getBytes().length;
this.length += (position == null || "".equals(position.trim())) ? 0
: position.getBytes().length;
this.length += String.valueOf(salary).getBytes().length;
}
// Get basic user information
public void printUserBaseInfo() {
System.out.println("|" + this.no + " " + this.name + " "
+ this.position + " " + this.salary);
}
// add employee information
public abstract void add(Staff staff);
// delete employee
public abstract Staff remove(String no);
// print employee information
public abstract void printEmployeesInfo(int layer);
// print some characters
protected void printChar(int layer) {
for (int j = 0; j < layer * 2; j++) {
System.out.print("-");
}
}
// private method prints a line
protected void printLine() {
System.out.print("+");
for (int i = 0; i < this.length + 4; i++) {
System.out.print("-");
}
System.out.println("-");
}
public String getNo() {
return no;
}
public void setNo(String no) {
this.no = no;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPosition() {
return position;
}
public void setPosition(String position) {
this.position = position;
}
public float getSalary() {
return salary;
}
public void setSalary(float salary) {
this.salary = salary;
}
}
2.2 Create a manager
package com.demo.composite.sub;
import java.util.ArrayList;
import com.demo.composite.Staff;
/**
* Managers (people with other employees)
*
* @author
*
*/
public class Manager extends Staff {
// store employee information
private final ArrayList<Staff> arrayList = new ArrayList<Staff>();
// Construction method
public Manager(String no, String name, String position, float salary) {
super(no, name, position, salary);
}
/**
* Add an employee
*/
@Override
public void add(Staff staff) {
this.arrayList.add(staff);
}
/**
* Delete employee information
*/
@Override
public Staff remove(String no) {
Staff staff = null;
if (no != null && !"".equals(no.trim())) {
for (int i = 0; i < this.arrayList.size(); i++) {
if (this.arrayList.get(i) == null) {
continue;
}
if (no.equals(this.arrayList.get(i).getNo())) {
staff = this.arrayList.remove(i);
break;
}
}
}
return staff;
}
/**
* Print employee information
*/
@Override
public void printEmployeesInfo(int layer) {
int tmpLayer = ++layer;
for (int i = 0; i < this.arrayList.size(); i++) {
if (this.arrayList.get(i) == null) {
continue;
}
// Print'-'
printChar(tmpLayer);
// print employee basic information
this.arrayList.get(i).printUserBaseInfo();
// print employee information
this.arrayList.get(i).printEmployeesInfo(tmpLayer);
}
}
}
2.3 Create ordinary employees
package com.demo.composite.sub;
import com.demo.composite.Staff;
/**
* Ordinary employees (people who really work)
*
* @author
*
*/
public class Employees extends Staff
{
// Construction method
public Employees(String no, String name, String position, float salary)
{
super(no, name, position, salary);
}
/**
* Add employee information
*/
@Override
public void add(Staff staff)
{
return;
}
/**
* Delete employee information
*/
@Override
public Staff remove(String no)
{
// directly return null
return null;
}
/**
* Print employee information
*/
@Override
public void printEmployeesInfo(int layer)
{
return;
}
}
2.4 Client Test
package com.demo;
import com.demo.composite.Staff;
import com.demo.composite.sub.Employees;
import com.demo.composite.sub.Manager;
/**
* Main application
*
* @author
*
*/
public class Client
{
/**
* @param args
*/
public static void main(String[] args)
{
// Company CEO
Staff boss = new Manager("1", "大老板", "CEO", 100000);
/**
* There are several department managers under the CEO
*/
// Finance Manager
Staff financeManager = new Manager("11", "Mr. Zhang", "Finance Manager", 60000);
// HR manager
Staff personnelManager = new Manager("12", "Mr. Wang", "Personnel Manager", 60000);
// technical manager
Staff technicalManager = new Manager("13", "Mr. Chen", "Technical Manager", 60000);
/**
* The technical department also has assistants and several supervisors
*/
// technical department assistant
Staff deptAssistant = new Manager("1301", "Assistant Wang", "Dept Assistant", 20000);
// Head of technical department 1
Staff deptManager1 = new Manager("1302", "Supervisor 1", "Technical Supervisor", 30000);
/**
* There are also software engineers under the technical director deptManager1 (the one who does the final work)
*/
Staff softwareEngineer1 = new Employees("1302001", "Zhang San", "Software Engineer", 5000);
Staff softwareEngineer2 = new Employees("1302002", "Li Si", "Software Engineer", 5500);
Staff softwareEngineer3 = new Employees("1302003", "Wang Wu", "Software Engineer", 4500);
// Add employee information for technical supervisor 1
deptManager1.add(softwareEngineer1);
deptManager1.add(softwareEngineer2);
deptManager1.add(softwareEngineer3);
// Head of technical department 2
Staff deptManager2 = new Manager("1303", "Supervisor 2", "Technical Supervisor", 30000);
// Added for Technical Manager: Department Assistant, Technical Supervisor 1 and Technical Supervisor 2
technicalManager.add(deptAssistant);
technicalManager.add(deptManager1);
technicalManager.add(deptManager2);
// Marketing Manager
Staff marketingManager = new Manager("14", "Mr. Wu", "Marketing Manager", 60000);
// Added for CEO: Finance Manager, HR Manager, Technical Manager and Marketing Manager
boss.add(financeManager);
boss.add(personnelManager);
boss.add(technicalManager);
boss.add(marketingManager);
// print CEO info
boss.printUserBaseInfo();
// Print the employee information of the CEO
boss.printEmployeesInfo(1);
}
}
The results are as follows:
|1 Big Boss CEO 100000.0
----|11 Mr. Zhang, Manager of Finance Department 60000.0
----|12 Mr. Wang, Manager of Personnel Department 60000.0
----|13 Mr. Chen, Manager of Technical Department 60000.0
------|1301 Assistant Wang Department Assistant 20000.0
------|1302 Supervisor 1 Technical Supervisor 30000.0
--------|1302001 Zhang San Software Engineer 5000.0
--------|1302002 Li Si Software Engineer 5500.0
-- ------|1302003 Wang Wu Software Engineer 4500.0
------|1303 Supervisor 2 Technical Supervisor 30000.0
----|14 Wu General Manager of Marketing Department 60000.0
Three principles of pattern design
1 Unified treatment of individual objects and composite objects
2 Abstract-oriented programming
Four use cases
1 When you want to represent a "part-whole" hierarchy of objects.
2 When users are expected to ignore the difference between a composite object and a single object, the user will use all the objects in the composite structure uniformly.
The static class diagram of the combined mode is as follows