Java 泛型在API中的体现

超、凢脫俗 2022-06-13 08:10 207阅读 0赞

1. 首先创建Person类和两个子类 Worker类和Student类

/\* person 类\*/

public class Person implements Comparable<Person> \{  
private String name;  
private int age;

public Person() \{  
super();  
\}  
  
public Person(String name, int age) \{  
super();  
this.name = name;  
this.age = age;  
\}  
  
       // 省略 getter 和 setter方法  
  
@Override  
public String toString() \{  
return "Person \[name=" + name + ", age=" + age + "\]";  
\}  
  
@Override  
public int compareTo(Person o) \{   // 按年龄排序  
int temp = this.age - o.age;  
return temp == 0 ? this.name.compareTo(o.name) : temp;  
\}  
  
\}

/\* student 类 \*/

public class Student extends Person \{

public Student() \{  
super();  
\}  
  
public Student(String name, int age) \{  
super(name, age);  
\}  
  
@Override  
public String toString() \{  
return "Student \[name()=" + getName() + ", age()=" + getAge() + "\]";  
\}  
\}

/\* worker 类 \*/

public class Worker extends Person \{  
  
public Worker() \{  
super();  
\}  
  
public Worker(String name, int age) \{  
super(name, age);  
\}  
  
@Override  
public String toString() \{  
return "Worker \[name()=" + getName() + ", age()=" + getAge()+ "\]";  
\}  
\}

/\*\* -------------------------------------------------泛型上限的体现--------------------------------------------------------\*/

/\*\*  
 \* @作者 atyang  
 \*   
 \*      TreeSet(Collection<? extends E> c) ：上限的体现,,类型可以是 E或E的子类型  
 \*/  
public class UpDemo \{  
  
public static void main(String\[\] args) \{  
  
// 创建一个collection集合  
//Collection<Person> c = new ArrayList<Person>();  
//c.add(new Person("lisi", 18));  
//c.add(new Person("aangwu", 23));  
  
Collection<Student> c2 = new ArrayList<Student>();  
c2.add(new Student("lisi", 18));  
c2.add(new Student("aangwu", 23));  
  
/\*  
\* TreeSet 集合在创建时就将 c 存入TreeSet集合中  
\*   
\* TreeSet 集合中传入的Collection集合存储的元素类型可以是 Person ,也可以是 person的子类型  
\* TreeSet<T> person = new TreeSet<T>(Collection<? extends T> c);  
\*/  
TreeSet<Person> person = new TreeSet<Person>(c2);       // c2 即满足 Collection<? extends T>  
person.add(new Person("zhangsan", 21));  
  
  
for (Iterator<Person> it = person.iterator(); it.hasNext();) \{  
Person person2 = it.next();  
System.out.println(person2);  
\}  
\}  
\}  
  
/\*  
  class TreeSet<E> \{  
      TreeSet<E>(Collection<? extends E> c)\{ \}  
  \}  
 \*/

/\*\*----------------------------------------------------------------泛型下限的体现----------------------------------------------\*/

/\*\*  
 \* @作者 at杨  
 \*   
 \*     泛型中下限在 API中的体现 TreeSet(Comparator<? super E> comparator)，，常用在比较器中  
 \*/  
public class DownDemo \{  
  
public static void main(String\[\] args) \{  
  
// 创建一个集合存储的是学生对象,按姓名排序  
/\*  
\* TreeSet 集合在创建时传入一个比较器，  
\* 比较器的参数类型可以是该集合的参数类型，也可以定义为该集合参数类型的父类类型  
\*    
\* TreeSet<T> person = new TreeSet<T>(Comparator<? super T> c);  
\*/  
TreeSet<Student> stu = new TreeSet<Student>(new comparaByName());  
stu.add(new Student("aaa", 18));  
stu.add(new Student("aab", 21));  
stu.add(new Student("abcc", 23));  
  
for (Iterator<Student> it = stu.iterator(); it.hasNext();) \{  
Student ts = it.next();  
System.out.println(ts);  
\}  
  
// 让工人按姓名排序  
TreeSet<Worker> wok = new TreeSet<Worker>(new comparaByName());  
wok.add(new Worker("aaa", 18));  
wok.add(new Worker("aab", 22));  
wok.add(new Worker("abcc", 23));  
  
for (Iterator<Worker> it = wok.iterator(); it.hasNext();) \{  
Worker wo = it.next();  
System.out.println(wo);  
\}  
\}  
\}  
  
/\*  
 \* 以下两个比较器，都是按照姓名进行排序，就是类型不同，一个是Student，一个是Worker 既然使用的都是  
 \* Person的内容，为什么不定义一个 Person 的比较器？  
 \*/  
class comparaByName implements Comparator<Person> \{  
  
@Override  
public int compare( Person o1 ,  Person o2) \{  
int temp = o1.getName().compareTo(o2.getName());  
return temp == 0 ? o1.getAge() - o2.getAge() : temp;  
\}  
\}  
// 定义一个比较器，排序学生  
/\*  
class comparaByName implements Comparator<Student> \{  
  
@Override  
public int compare(Student o1, Student o2) \{  
int temp = o1.getName().compareTo(o2.getName());  
return temp == 0 ? o1.getAge() - o2.getAge() : temp;  
\}  
\}  
\*/  
  
// 定义一个比较器，排序工人  
/\*  
class comparaWorkByName implements Comparator<Worker> \{  
  
@Override  
public int compare(Worker o1, Worker o2) \{  
int temp = o1.getName().compareTo(o2.getName());  
return temp == 0 ? o1.getAge() - o2.getAge() : temp;  
\}  
  
\}

\*/  
  
/\*  
 TreeSet<E>\{   
 TreeSet<E>(Comparator(? super E))\{ \};  
\}  
 \*/