一对多:
一个教室对应多个学生.
学校里边不同的班级有不同的学生,但是可能ID相同.
//优化过后的代码,更具有复用和扩展性.
//定义一个可以存放三个数据的集合——班级名称,学生ID,学生名称
import java.util.*;
class MyMap
{
private Map map;
MyMap()
{
map = new HashMap();
}
public void createClass(String className,String id, String name)
{
Map subMap =(Map)map.get(className);
if (subMap == null)
{ subMap = newHashMap();
map.put(className,subMap); //已经存在班级,只需要向学生这个Map集合里边存数据,而班级的Map不需要再存了
}
subMap.put(id, name);
}
public String getName(String className, Stringid)
{
Map subMap =(Map)map.get(className);
return(String)subMap.get(id);
}
public void getStudent(String className)
{
System.out.println(className);
Map subMap =(Map)map.get(className);
Set mySet =subMap.keySet();
for (Iterator it =mySet.iterator(); it.hasNext(); )
{
String id =(String)it.next();
String name =(String)subMap.get(id);
System.out.println(id+ "..." + name);
}
}
public void getAll()
{
Set set1 = map.keySet();
for (Iterator it =set1.iterator(); it.hasNext(); )
{
StringclassName = (String)it.next();
System.out.println(className);
Map subMap= (Map)map.get(className);
Set set2 =subMap.keySet();
for (Iteratorit1 = set2.iterator(); it1.hasNext(); )
{
Stringid = (String)it1.next();
Stringname = (String)subMap.get(id);
System.out.println(it+ "..." + name);
}
}
}
}
class MyMapDemo
{
public static void main(String[] args)
{
MyMap mm = new MyMap();
mm.createClass("班级一", "01","小张");
mm.createClass("班级一", "02","小王");
mm.createClass("班级一", "03","小李");
mm.createClass("班级二", "01","小A");
mm.createClass("班级二", "02","小B");
mm.createClass("班级二", "03","小C");
//System.out.println(mm.getName("班级一","02"));
//mm.getStudent("班级一");
//mm.getStudent("班级二");
mm.getAll();
}
}
//前期设计代码,不具备扩展性和复用性.
import java.util.*;
class MapDemo
{
public static void main(String[] args)
{
//初期设计————(代码缺少复用性,冗余)
//定义一个学校,里边可以有多个班级
HashMap <String,HashMap> school = new HashMap<String,HashMap>();
//班级一
HashMap<String,String> class1 = new HashMap<String,String>();
class1.put("01", "小张");
class1.put("02", "小王");
class1.put("03","小李");
//班级二
HashMap<String,String> class2 = new HashMap<String,String>();
class2.put("01", "小周");
class2.put("02", "小孙");
class2.put("03", "小赵");
school.put("班级一", class1);
school.put("班级二",class2);
show(school);
}
public static void show(Map map)
{
Set<String>s = map.keySet();
for(Iterator<String> it = s.iterator();it.hasNext(); )
{
StringclassName = it.next();
System.out.println(className);
Map hs =(Map)map.get(className);
Set<String> s1 = hs.keySet();
for (Iterator<String> it1 = s1.iterator();it1.hasNext(); )
{
Stringid = it1.next();
Stringname = (String)hs.get(id);
System.out.println(id+".."+name);
}
}
}
}