java 泛型extends和super的区别

假设有Employee以及Manager两个类，Employee是Manager的父类。

public class Employee {
    private String name;
    private double salary;

    public Employee(String name, double salary) {
        this.name = name;
        this.salary = salary;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getSalary() {
        return salary;
    }

    public void setSalary(double salary) {
        this.salary = salary;
    }
}

public class Manager extends Employee {

    public Manager(String name, double salary) {
        super(name, salary);
    }
    public void modifySalary(Employee e,double salary) {
        e.setSalary(salary);
    }
}

以及将两个员工进行配对的类Pair

public class Pair<T> {
    private T first;
    private T second;

    public Pair() {
        first = null;
        second = null;
    }

    public Pair(T first, T second) {
        this.first = first;
        this.second = second;
    }

    public T getFirst() {
        return first;
    }

    public void setFirst(T first) {
        this.first = first;
    }

    public T getSecond() {
        return second;
    }

    public void setSecond(T second) {
        this.second = second;
    }
}

下面代码具体阐释二者区别,<? extentds ...>主要用于读，< ? super ...>主要用于写

public class PairTest {
    public static void main(String[] args) {
        Manager ceo = new Manager("nike", 1000);
        Manager cfo = new Manager("tom", 2000);
        Pair<Manager> buddies = new Pair<>(ceo, cfo);
        printBuddies(buddies);

        Manager[] managers = { ceo, cfo };
        Pair<Employee> result = new Pair<>();
        minmaxSalary(managers, result);
        System.out
                .println("first name:" + result.getFirst().getName() + ",second name:" + result.getSecond().getName());
        maxminSalary(managers, result);
        System.out
                .println("first name:" + result.getFirst().getName() + ",second name:" + result.getSecond().getName());
    }

    /**
     * 这里确定上界，参数是Employee或者其子类
     * 
     * @param p
     */
    public static void printBuddies(Pair<? extends Employee> p) {
        Employee first = p.getFirst();
        Employee second = p.getSecond();
        System.out.println("first name:" + first.getName() + "  second name:" + second.getName());

    }

    /**
     * 这里确定下界，参数可以是Manager或者其父类
     * 
     * @param a
     * @param result
     */
    public static void minmaxSalary(Manager[] a, Pair<? super Manager> result) {
        if (a.length == 0)
            return;

        Manager min = a[0];
        Manager max = a[0];

        for (int i = 0; i < a.length; i++) {
            if (a[i].getSalary() > max.getSalary())
                max = a[i];
            if (a[i].getSalary() < min.getSalary())
                min = a[i];
        }

        result.setFirst(min);
        result.setSecond(max);
    }

    public static void maxminSalary(Manager[] a, Pair<? super Manager> result) {
        minmaxSalary(a, result);
        swap(result);
    }

    public static <T> void swap(Pair<T> p) {
        T t = p.getFirst();
        p.setFirst(p.getSecond());
        p.setSecond(t);
    }
}