集合框架-泛型-泛型下限

package cn.itcast.p5.generic.advance.demo;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import cn.itcast.p2.bean.Person;
import cn.itcast.p2.bean.Student;

public class GenericAdvanceDemo3 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ArrayList<Person> al = new ArrayList<Person>();
        
        al.add(new Person("abc",30));
        al.add(new Person("abc4",34));
        
        ArrayList<Student> al2 = new ArrayList<Student>();
        al2.add(new Student("stu1",11));
        al2.add(new Student("stu2",22));
        
        ArrayList<String> al3 = new ArrayList<String>();
        al3.add("stu3331");
        al3.add("stu33332");

        
        printCollection2(al);
        printCollection2(al2);
//        printCollection(al3);

        
        
        
    }

    /**
     * 迭代并打印集合中元素。
     * 
     * 可以对类型进行限定：
     * ? extends E:接收E类型或者E的子类型对象。上限！
     * 
     * ? super E:接收E类型或者E的父类型。下限！
     * 
     * 
     * @param al
     */
//    public static void printCollection(Collection<? extends Person > al) {//Collecton可以接收所有集合
//                                                            //Collection<Person> al = new ArrayList<Student>();
//                                                            //不行泛型不匹配
//        Iterator<? extends Person > it = al.iterator();//取得时候泛型限定，可以调用父类的方法
//        
//        while(it.hasNext()) {
////            String str = it.next();
////            System.out.println(str);
////            System.out.println(it.next());
//            Person p = it.next();
//            System.out.println(p.getName()+":"+p.getAge());
//        }
//    }
    /*
     * public static <T> T printCollection(Collection<T> al) {// Iterator<T> it =
     * al.iterator();
     * 
     * while(it.hasNext()) { // T str =
     * it.next();//虽然这个和Collection加？区别不大，但是这里的T能代表一个具体的类型可被访问 //
     * System.out.println(str); // System.out.println(it.next()); T t = it.next();
     * return t;//可能返回值会用到T，Collection加？用于无此返回值 } }
     */
    public static void printCollection2(Collection<? super Student> al) {
        Iterator<? super Student > it = al.iterator();//取得时候泛型限定，可以调用父类的方法
        
        while(it.hasNext()) {
//            String str = it.next();
//            System.out.println(str);
//            System.out.println(it.next());
//            Person p = it.next();
//            System.out.println(p.getName()+":"+p.getAge());
            System.out.println(it.next());
        }
        
    }
        
        

}

package cn.itcast.p2.bean;

public class Person implements Comparable<Person>{
    private String name;
    private int age;
    
    
    public Person() {
        super();
        // TODO Auto-generated constructor stub
    }
    
    public Person(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }
    public int compareTo(Person p) {//指定比较类型，传入比较类型
//        Person p= (Person)obj;
        int temp = this.age-p.age;
        return temp==0?this.name.compareTo(p.name):temp;
    }
    
    
//    @Override
//    public boolean equals(Object obj) {//不能把Object改为Person，equals方法来自Object，Object没有定义泛型
//        // TODO Auto-generated method stub
//        if (this == obj) {
//            return true;
//        }
//        if (!(obj instanceof Person)) {
//            throw new RuntimeException()
//        }
//        Person p = (Person)obj;
//        return super.equals(obj);
//    }
    /*
     * @Override public int hashCode() { final int prime = 31; int result = 1;
     * result = prime * result + age; result = prime * result + ((name == null) ? 0
     * : name.hashCode()); return result; }
     * 
     * @Override public boolean equals(Object obj) { if (this == obj) return true;
     * if (obj == null) return false; if (getClass() != obj.getClass()) return
     * false; Person other = (Person) obj; if (age != other.age) return false; if
     * (name == null) { if (other.name != null) return false; } else if
     * (!name.equals(other.name)) return false; return true; }//alt+shift+s
     * hashCode和equals
     */
    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;
    }
    
}

package cn.itcast.p2.bean;

public class Student extends Person {

    public Student() {
        super();
        // TODO Auto-generated constructor stub
    }

    public Student(String name, int age) {
        super(name, age);
        // TODO Auto-generated constructor stub
    }

    @Override
    public String toString() {
        // TODO Auto-generated method stub
        return "Student:"+getName()+":"+getAge();
    }
    
}

package cn.itcast.p2.bean;

public class Worker extends Person {

    public Worker() {
        super();
        // TODO Auto-generated constructor stub
    }

    public Worker(String name, int age) {
        super(name, age);
        // TODO Auto-generated constructor stub
    }

    @Override
    public String toString() {
        // TODO Auto-generated method stub
        return "Worker:"+getName()+":"+getAge();
    }
    
    
}