JAVA8--List.stream().collect

package mypack;

import java.text.ParseException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;


public class Test
{
	public static void main(String[] args) throws ParseException
	{
		Student s1 = new Student("1", "S1", 10);
		Student s2 = new Student("1", "S1", 10);
		Student s3 = new Student("1", "S1", 10);
		Student s4 = new Student("2", "S2", 20);
		Student s5 = new Student("2", "S2", 20);
		Student s6 = new Student("2", "S2", 20);
		Student s7 = new Student("3", "S3", 30);
		Student s8 = new Student("3", "S3", 30);
		Student s9 = new Student("4", "S4", 40);
		Student s10 = new Student("4", "S4", 40);
		
		List<Student> sList = new ArrayList<Student>();
		sList.add(s1);
		sList.add(s2);
		sList.add(s3);
		sList.add(s4);
		sList.add(s5);
		sList.add(s6);
		sList.add(s7);
		sList.add(s8);
		sList.add(s9);
		sList.add(s10);
		
		Map<ParentStudent, List<Student>> sMap = sList.stream().collect(Collectors.groupingBy(student -> new ParentStudent(student.getId())));
		
		sMap.forEach((key, value) -> {
            System.out.print("id:" + key.getId() + "====");
            for(Student s : value)
            {
            	System.out.print("name:" + s.getName() + ",");
            }
            System.out.println("");
        });
	}

}

class ParentStudent extends SupperStudent
{
	String id;
	
	public ParentStudent(String sid)
	{
		this.id = sid;
	}
	
	@Override
	public int hashCode()
	{
		final int prime = 31;
		int result = 1;
		result = prime * result + ((id == null) ? 0 : id.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj)
	{
		if(this == obj)
			return true;
		if(obj == null)
			return false;
		if(getClass() != obj.getClass())
			return false;
		ParentStudent other = (ParentStudent)obj;
		if(id == null)
		{
			if(other.id != null)
				return false;
		}
		else if(!id.equals(other.id))
			return false;
		return true;
	}

	public String getId()
	{
		return id;
	}

	public void setId(String id)
	{
		this.id = id;
	}

}

class SupperStudent
{
	private String sex;

	public String getSex()
	{
		return sex;
	}

	public void setSex(String sex)
	{
		this.sex = sex;
	}
	
}

class Student
{
	String id;
	String name;
	int age;
	
	public Student(String sid)
	{
		this.id = sid;
	}
	
	public Student(String sid, String sname, int sage)
	{
		this.id = sid;
		this.name = sname;
		this.age = sage;
	}

	public String getId()
	{
		return id;
	}

	public void setId(String id)
	{
		this.id = id;
	}

	public String getName()
	{
		return name;
	}

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

	public int getAge()
	{
		return age;
	}

	public void setAge(int age)
	{
		this.age = age;
	}

}