Java基础之泛型下限的体现-蒲公英云

Java基础之泛型下限的体现

小鱼儿 2022-12-10 08:39 230阅读 0赞

package cn.itcast.p5.generic.advance.demo;
import java.util.Comparator;
import java.util.Iterator;
import java.util.TreeSet;
import cn.itcast.p2.bean.Person;
import cn.itcast.p2.bean.Student;
import cn.itcast.p2.bean.Worker;
public class GenericAdvanceDemo4 {
    /**
     * @param args
     */
    public static void main(String[] args) {
        TreeSet<Person> al1 = new TreeSet<Person>(new CompByName());
        al1.add(new Person("abc4",34));
        al1.add(new Person("abc1",30));
        al1.add(new Person("abc2",38));
        TreeSet<Student> al2 = new TreeSet<Student>(new CompByName());
        al2.add(new Student("stu1",11));
        al2.add(new Student("stu7",20));
        al2.add(new Student("stu2",22));
        TreeSet<Worker> al3 = new TreeSet<Worker>();
        al3.add(new Worker("stu1",11));
        al3.add(new Worker("stu2",22));
        TreeSet<String> al4 = new TreeSet<String>();
        al4.add("abcdeef");
//        al1.addAll(al4);//错误，类型不匹配。
//        al1.addAll(al2);
//        al1.addAll(al3);
//        System.out.println(al1.size());
        Iterator<Student> it = al2.iterator();
        while(it.hasNext()){
            System.out.println(it.next());
        }
    }
}
/*
 * class TreeSet<Worker>
 * {
 *         Tree(Comparator<? super Worker> comp);
 * }
 * 
 * 什么时候用下限呢？通常对集合中的元素进行取出操作时，可以是用下限。
 * 
 */
class CompByName 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;
    }
}
class CompByStuName 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;
    }
}
class CompByWorkerName 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;
    }
}