Map集合小总结及两种取值方法 - 黑马程序员技术交流社区

class Student implements Comparable<Student> //让学生类具备可比较性
{
private String name;
private int age;
private String dizhi;
Student(String name,int age){
this.name = name;
this.age = age;
}
public int compareTo(Student s){
int num = new Integer(this.age).compareTo(new Integer(s.age)); //用Integer类型比较年龄大小，返回正，负，0
if(num ==0)
return this.name.compareTo(s.name); //比较name
return num;
}
public int hashCode(){ //重写Code方法比较哈希值
return name.hashCode()+age*34;
}
public boolean equals(Object obj){ //重写equals方法，按需求来比较
if(!(obj instanceof Student))
throw new ClassCastException("不是学生类型"); //当传入不是学生类时抛出数据类型不匹配异常
Student s = (Student)obj; //是学生类就强转
return this.name.equals(s.name) && this.age == s.age; //返回比较后的值
}
public String getName(){
return name;
}
public int getAge(){
return age;
}
public String toString(){ //重写toString方法
return name+"--"+age;
}
}
class MapTest
{
public static void main(String[] args)
{
Map<Student,String> map = new HashMap<Student,String>(); //定义泛型接收对象为Student类和String
map.put(new Student("z3",20),"bj");
map.put(new Student("z2",21),"bj1");
map.put(new Student("z6",23),"bj3");
map.put(new Student("z4",21),"bj6");
map.put(new Student("z7",11),"bj1");
Set<Student> keyset = map.keySet(); //第一种获取方法用key值获取value值
Iterator<Student> it = keyset.iterator();
while(it.hasNext())
{
Student s = it.next();
String addr = map.get(s);
System.out.println(s+"------"+addr);
}
Set<Map.Entry<Student,String>> entryset = map.entrySet(); //第二种获取方法通过集合中的映射关系取出，Map.Entry类型
Iterator<Map.Entry<Student,String>> ite = entryset.iterator();
while(ite.hasNext()){
Map.Entry<Student,String> me = ite.next();
Student stu = me.getKey();
String value = me.getValue();
System.out.println(stu+"---"+value);
}
}
}

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