父子类的问题

public class ParentClass {

    /** Creates a new instance of ParentClass */
    protected ParentClass() {
    }



}public class SubClass extends ParentClass{

    ParentClass pc;//=new super();
    /** Creates a new instance of SubClass */
    public SubClass() {
        super();
    }
    public void setPc(){
        pc=new super();
    }
}为何子类中无法用super()来构造父类对象