List分组

package com.common.main.mapAndList;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;


public class Student {
	private String classId;

	private String studentId; // 学号

	private String studentName; // 姓名

	private String sex; // 性別 0 男 1 女

	public String getClassId() {
		return classId;
	}

	public void setClassId(String classId) {
		this.classId = classId;
	}

	public String getSex() {
		return sex;
	}

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

	public String getStudentId() {
		return studentId;
	}

	public void setStudentId(String studentId) {
		this.studentId = studentId;
	}

	public String getStudentName() {
		return studentName;
	}

	public void setStudentName(String studentName) {
		this.studentName = studentName;
	}
	
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		List studentAllList = null ;// 所以班級的学生
		
		//步骤1
		Map<String ,List> map = new HashMap<String ,List>();
		Map<String ,Object> mapLast = new HashMap<String ,Object>();
//		for(Student student : studentAllList){
		for(Iterator it = studentAllList.iterator();it.hasNext();){
			Student student = (Student)it.next();

			if(map.containsKey(student.getClassId())){ //如果已经存在这个数组，就放在这里
				List studentList = map.get(student.getClassId());
				studentList.add(student);
			}else{
				List studentList = new ArrayList();  //重新声明一个数组list
				studentList.add(student);
				map.put(student.getClassId(), studentList);
			}
		}
		
//		步骤2 
//		利用 处理1 步骤 分组完的数据 ,按性别 男/女  再次分组
		for(Map.Entry<String, List> m: map.entrySet()){ //按键值遍历 Map
			Map mapList = new HashMap(); //
			
			List studentSingle  = m.getValue(); //同一班级的学生，男女
			List studentListMen = new ArrayList(); // 声明一个存放男生的 list
			List studentListWomen = new ArrayList(); // 声明一个存放女生的 list
			for(Iterator it = studentSingle .iterator();it.hasNext();){//遍历
				Student student = (Student)it.next();
				if("0".equals(student.getSex())){ //男生
					studentListMen.add(student);  //男生
				}else{
					studentListWomen.add(student); //女生
				}
			}
			mapLast.put("班级", m.getKey());
			mapLast.put("学生 男", studentListMen);
		}
	}
}