Java-泛型

public class Order {
    String rderName;
    int orderId;

    T orderT;

    public Order() {
        //编译不通过
        //T[] t=new T[10];
        //编译通过
        T[] t=(T[])new Object[10];
    }

    public Order(String rderName, int orderId, T orderT) {
        this.rderName = rderName;
        this.orderId = orderId;
        this.orderT = orderT;
    }
    public T getOrderT() {
        return orderT;
    }

    public void setOrderT(T orderT) {
        this.orderT = orderT;
    }

    @Override
    public String toString() {
        return "Order{" +
                "rderName='" + rderName + ''' +
                ", orderId=" + orderId +
                ", orderT=" + orderT +
                '}';
    }
    
}

public class SubOrder extends Order{//不是泛型

}

public class SubOrder1 extends Order {//仍然是泛型
}

//异常类不能是泛型的
    @Test
    public void test1(){

        Order order=new Order();
        order.setOrderT("sdjf");
        order.setOrderT(345);
        //建议实例化时指明累的泛型
    }

    @Test
    public void test2(){
        //子类继承带泛型的父类时，指明的泛型类型，则实例化子类对象时，不再需要指明泛型
        SubOrder so=new SubOrder();
        so.setOrderT(123);

        SubOrder1 sob1=new SubOrder1<>();
        sob1.setOrderT("sskksks");
    }

    @Test
    public void test3(){
        //泛型不同的引用不能相互赋值
        ArrayList al1=null;
        ArrayList al2=null;
//        al1=al2;
    }

public class Student extends Person{
}

public class Person {
}

    @Test
    public void test4(){
        //通配符 ?
        //类A是是类B的父类 G和G是没有关系的二者共同的父类是：G
        List