inheritance

问题 Suppose I have 2 classes ........ A Class is base class and class B is derived class and if i create a reference such as : A a=new B(); does it mean that reference a points to object of B Class ? If yes than how am i able to call overridden methods of A in B and not other methods of B ? thank you in advance class A { m1() { } } class B extends A { m1() { } m2() { } } A a=new B(); a.m1(); //it will call overridden m1() in B a.m2(); //it doesnt work if reference "a" points to object of B than

问题 The original question stems from this question: Why is this JPA 2.0 mapping giving me an error in Eclipse/JBoss Tools? As you can see this constellation also freaks out the Eclipse Dali JPA validator. The JPA spec seems to allow this as seen here (somewhat reliable): Does the JPA specification allow references to non-primary key columns? The exact code posted in the first question also raises a Hibernate MappingException: Exception in thread "main" javax.persistence.PersistenceException:

问题 I have a simple SqlAlchemy application: import sqlalchemy as sa import sqlalchemy.ext.declarative as dec import sqlalchemy.engine.url as saurl import sqlalchemy.orm as saorm import sqlalchemy.schema as sch import abc class ItemTable(): __tablename__ = 'book_items' @abc.abstractmethod def _source_key(self): pass rowid = sa.Column(sa.Integer, sa.Sequence('book_page_id_seq'), primary_key=True) src = sa.Column(sa.String, nullable=False, index=True, default=_source_key) dlState = sa.Column(sa

问题 I'm currently working on a port of an existing library which makes use of ostream to write to a terminal. The ostream was derived as part of the port. The ostream derivative class used is defined as so: class owstream: public std::ostream { public: CTerminal * output; giac::context * contextptr; owstream(CTerminal *, giac::context * contextptr , int = 0); virtual ~owstream(); }; This is used to output some data, typically integers and doubles. The problem is that the platform I'm working on

问题 I'm currently working on a port of an existing library which makes use of ostream to write to a terminal. The ostream was derived as part of the port. The ostream derivative class used is defined as so: class owstream: public std::ostream { public: CTerminal * output; giac::context * contextptr; owstream(CTerminal *, giac::context * contextptr , int = 0); virtual ~owstream(); }; This is used to output some data, typically integers and doubles. The problem is that the platform I'm working on

问题 Among my models, I have Exercise which has a m2m link to Workout. I also have WorkoutPlan and LogBook which are types of Workouts. WorkoutPlan is where ideal workouts are stored. LogBook is where a user stores the workout they actually completed. They can also link a LogBook to a WorkoutPlan to indicate that the actual performance was connected to an original ideal plan. class Exercise(NameDescModel): muscles = models.ManyToManyField(Muscle, blank=True) groups = models.ManyToManyField(Group,

问题 Among my models, I have Exercise which has a m2m link to Workout. I also have WorkoutPlan and LogBook which are types of Workouts. WorkoutPlan is where ideal workouts are stored. LogBook is where a user stores the workout they actually completed. They can also link a LogBook to a WorkoutPlan to indicate that the actual performance was connected to an original ideal plan. class Exercise(NameDescModel): muscles = models.ManyToManyField(Muscle, blank=True) groups = models.ManyToManyField(Group,

问题 I have my own control: public class newControl : Control { } There is a Text property, but there is not a TextAlign property. For example, I need this property similar to the TextAlign property of a Button , but I don't want inherit it from a button class. So can I inherit only TextAlign property? If yes, how? 回答1: Yes, you can just add it. The built in enumeration is called ContentAlignment : using System.ComponentModel; using System.Windows.Forms; public class newControl : Control { private

问题 In chapter 6 (Code Reuse Patterns) there is following example: // the parent constructor function Parent(name) { this.name = name || 'Adam'; } // adding functionality to the prototype Parent.prototype.say = function () { return this.name; }; // empty child constructor function Child(name) {} // inheritance magic happens here inherit(Child, Parent); In section "Classical Pattern #1 — The Default Pattern" the implementation of the inherit() function is: function inherit(C, P) { C.prototype =

问题 In chapter 6 (Code Reuse Patterns) there is following example: // the parent constructor function Parent(name) { this.name = name || 'Adam'; } // adding functionality to the prototype Parent.prototype.say = function () { return this.name; }; // empty child constructor function Child(name) {} // inheritance magic happens here inherit(Child, Parent); In section "Classical Pattern #1 — The Default Pattern" the implementation of the inherit() function is: function inherit(C, P) { C.prototype =