Java学习笔记19 泛型、TreeMap、Co…

泛型是类型的参数表示，简单的几种应用形式：（作用，更小的类型转换抛出，只要编译时没出现警告，就不会出现运行时ClassCastException无需记向下转换的具体类型）

 

1.class Text<T>//以String类型实例化泛型T为例

  Text<String> text = new Text<String>();

2.class Text<T extends List>//只有List的实现类才能作为参数传入

  Text<LinkedList> text = new Text<LinkedList>();

3.class Text<T> //限定类型持有者的范围

  Text<? extends Set>  text= null;

  text = Text<HashSet>();

 

import java.util.Comparator;

import java.util.Iterator;

import java.util.Map;

import java.util.Set;

import java.util.TreeMap;

public class MapTest

{

public static void main(String[] args) 

{

TreeMap<Person,String> map = new TreeMap<Person,String>(new Person2<Person>());

map.put(new Person("zhangsan",15,"beijing"), "第一名");

map.put(new Person("lisi",20,"tianjin"),"第二名");

map.put(new Person("wangwu ",25,"shagnhai"), "第三名");

Set<Map.Entry<Person,String>> set = map.entrySet();

for(Iterator<Map.Entry<Person,String>> itr = set.iterator(); itr.hasNext();)

{

Map.Entry<Person,String> mentry = itr.next();

int age = (mentry.getKey()).getAge();

System.out.println(age);

System.out.println(mentry.getValue());

}

}

}

class Person2<T> implements Comparator<T>

{

public int compare(T o1,T o2)

{

Person p1 = (Person)o1;

Person p2 = (Person)o2;

return p1.age - p2.age;

}

}

class Person

{

String name;

int age;

String address;

public Person(String name, int age, String address)

{

this.name = name;

this.address= address;

this.age = age;

}

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;

}

public String getAddress() {

return address;

}

public void setAddress(String address) {

this.address = address;

}

}