1.3.5_250_abstract_Abstracttemplet5_1_1

abstract在java中用法(一)Abstract在Java中在Java中，abstract是一个关键字，用于定义抽象类和抽象方法。

抽象类是一种特殊的类，不能被实例化，只能用作其他类的基类。

抽象方法是一种没有具体实现的方法，只有方法声明，没有方法体。

下面将详细讲解abstract在Java中的用法。

抽象类抽象类是一种用abstract关键字修饰的类。

它不能被实例化，只能作为父类被继承。

抽象类的主要作用是定义子类需要实现的一组方法，子类必须实现这些方法才能被实例化。

定义抽象类的语法如下：abstract class AbstractClass {// 抽象方法public abstract void abstractMethod();// 普通方法public void normalMethod() {// 方法实现}}抽象类可以包含抽象方法和普通方法。

抽象方法用abstract关键字修饰，没有方法体；普通方法有方法体。

抽象类可以包含普通成员变量和静态成员变量，也可以包含普通方法和静态方法。

但是不能创建抽象类的实例。

抽象方法抽象方法是一种没有具体实现的方法，只有方法声明。

抽象方法用abstract关键字修饰，没有方法体。

抽象方法必须在抽象类中声明，子类必须实现这些抽象方法才能被实例化。

定义抽象方法的语法如下：abstract void abstractMethod();抽象方法也可以包含参数和返回值，用于定义子类必须实现的方法签名。

子类继承抽象类后，必须实现抽象方法，否则子类也必须声明为抽象类。

继承抽象类子类继承抽象类后，必须实现抽象类中的所有抽象方法才能被实例化。

子类可以通过覆盖抽象方法来实现具体的功能。

如果子类不想实现某个抽象方法，那么子类也必须声明为抽象类。

继承抽象类的语法如下：class ConcreteClass extends AbstractClass {// 实现抽象方法public void abstractMethod() {// 方法实现}// 覆盖普通方法public void normalMethod() {// 方法实现}}注意，如果一个类继承了抽象类，但没有实现抽象方法，则该类必须声明为抽象类。

C#中abstract的⽤法详解abstract可以⽤来修饰类,⽅法,属性,索引器和时间,这⾥不包括字段. 使⽤abstrac修饰的类,该类只能作为其他类的基类,不能实例化,⽽且abstract修饰的成员在派⽣类中必须全部实现,不允许部分实现,否则编译异常. 如:using System;namespace ConsoleApplication8{class Program{static void Main(string[] args){BClass b = new BClass();b.m1();}}abstract class AClass{public abstract void m1();public abstract void m2();}class BClass : AClass{public override void m1(){throw new NotImplementedException();}//public override void m2()//{// throw new NotImplementedException();//}}}Abstract classes have the following features:抽象类拥有如下特征:1,抽象类不能被实例化, 但可以有实例构造函数, 类是否可以实例化取决于是否拥有实例化的权限 (对于抽象类的权限是abstract, 禁⽌实例化),即使不提供构造函数, 编译器也会提供默认构造函数;2,抽象类可以包含抽象⽅法和访问器;3,抽象类不能使⽤sealed修饰, sealed意为不能被继承;4,所有继承⾃抽象类的⾮抽象类必须实现所有的抽象成员,包括⽅法,属性,索引器,事件;abstract修饰的⽅法有如下特征:1,抽象⽅法即是虚拟⽅法(隐含);2,抽象⽅法只能在抽象类中声明;3,因为抽象⽅法只是声明, 不提供实现, 所以⽅法只以分号结束,没有⽅法体,即没有花括号部分;如public abstract void MyMethod();4,override修饰的覆盖⽅法提供实现,且只能作为⾮抽象类的成员;5,在抽象⽅法的声明上不能使⽤virtual或者是static修饰.即不能是静态的,⼜因为abstract已经是虚拟的,⽆需再⽤virtual强调.抽象属性尽管在⾏为上与抽象⽅法相似,但仍有有如下不同:1,不能在静态属性上应⽤abstract修饰符;2,抽象属性在⾮抽象的派⽣类中覆盖重写,使⽤override修饰符;抽象类与接⼝:1,抽象类必须提供所有接⼝成员的实现;2,继承接⼝的抽象类可以将接⼝的成员映射位抽象⽅法.如:interface I{void M();}abstract class C: I{public abstract void M();}抽象类实例:// abstract_keyword.cs// 抽象类using System;abstract class BaseClass // 抽象类{protected int _x = 100; //抽象类可以定义字段,但不可以是抽象字段,也没有这⼀说法.protected int _y = 150;public BaseClass(int i) //可以定义实例构造函数,仅供派⽣的⾮抽象类调⽤; 这⾥显式提供构造函数,编译器将不再提供默认构造函数. {fielda = i;}public BaseClass(){}private int fielda;public static int fieldsa = 0;public abstract void AbstractMethod(); // 抽象⽅法public abstract int X { get; } //抽象属性public abstract int Y { get; }public abstract string IdxString { get; set; } //抽象属性public abstract char this[int i] { get; } //抽象索引器}class DerivedClass : BaseClass{private string idxstring;private int fieldb;//如果基类中没有定义⽆参构造函数,但存在有参数的构造函数,//那么这⾥派⽣类得构造函数必须调⽤基类的有参数构造函数,否则编译出错public DerivedClass(int p): base(p) //这⾥的:base(p)可省略,因为基类定义了默认的⽆参构造函数{fieldb = p;}public override string IdxString //覆盖重新属性{get{return idxstring;}set{idxstring = value;}}public override char this[int i] //覆盖重写索引器{get { return IdxString[i]; }}public override void AbstractMethod(){_x++;_y++;}public override int X // 覆盖重写属性{get{return _x + 10;}}public override int Y // 覆盖重写属性{get{return _y + 10;}}static void Main(){DerivedClass o = new DerivedClass(1);o.AbstractMethod();Console.WriteLine("x = {0}, y = {1}", o.X, o.Y);}}以上所述是⼩编给⼤家介绍的C#中abstract的⽤法详解，希望对⼤家有所帮助，如果⼤家有任何疑问请给我留⾔，⼩编会及时回复⼤家的。

Java中实现抽象类的步骤示例在Java中实现一个抽象类需要遵循以下步骤：1.使用abstract关键字声明抽象类：抽象类是一个特殊的类，它不能被直接实例化，只能被继承。

要声明一个抽象类，需要在类名前加上abstract关键字。

2.定义抽象方法：抽象方法是没有具体实现的，需要子类来实现。

在抽象类中定义抽象方法时，需要在方法名前加上abstract关键字。

3.实现非抽象方法：非抽象方法是可以直接在抽象类中实现的，不需要子类来实现。

在抽象类中实现非抽象方法时，需要在方法名前加上public或protected修饰符。

下面是一个示例代码，演示如何在Java中实现一个抽象类：abstract class AbstractAnimal {// 定义抽象方法abstract void makeSound();// 定义非抽象方法public void eat() {System.out.println("The animal eats.");}}在这个示例中，我们定义了一个名为AbstractAnimal的抽象类，它包含一个抽象方法makeSound()和一个非抽象方法eat()。

要使用这个抽象类，需要创建一个继承自AbstractAnimal的子类，并实现其中的抽象方法。

例如：class Dog extends AbstractAnimal {@Overridepublic void makeSound() {System.out.println("汪汪");}}在这个示例中，我们创建了一个名为Dog的子类，它继承了AbstractAnimal并实现了其中的抽象方法makeSound()。

现在我们可以使用Dog对象调用其中的方法，例如：Dog dog = new Dog();dog.eat(); // 输出 "The animal eats."dog.makeSound(); // 输出 "汪汪"。

abstract在c语言中的用法Abstract在C语言中的用法Abstract是C语言中的一个关键字，它用于定义抽象数据类型（ADT）。

抽象数据类型是一种数据类型，它的实现细节被隐藏在一个抽象层次之下，只有一组操作被公开。

这种数据类型的实现方式可以被修改，而不会影响到使用它的代码。

在C语言中，使用Abstract定义ADT需要使用struct结构体和指向结构体的指针。

下面是一个例子：```typedef struct {int data;void (*print)(int);} AbstractDataType;void printData(int data) {printf("Data: %d\n", data);}AbstractDataType* createADT(int data) {AbstractDataType* adt = (AbstractDataType*) malloc(sizeof(AbstractDataType));adt->data = data;adt->print = printData;return adt;}int main() {AbstractDataType* adt = createADT(10);adt->print(adt->data);free(adt);return 0;}```在这个例子中，我们定义了一个AbstractDataType结构体，它包含一个整数data和一个指向函数的指针print。

我们还定义了一个printData函数，它用于打印data的值。

createADT函数用于创建一个AbstractDataType对象，并将data和print函数指针初始化。

在main函数中，我们创建了一个AbstractDataType对象，调用了它的print函数，并释放了它的内存。

使用Abstract定义ADT的好处是，它可以将数据类型的实现细节隐藏起来，只公开一组操作。

abstractmethoderror method is abstract解决方法
`AbstractMethodError` 是一个在Java 中的错误，通常在以下情况下发生：
1. 当一个类实现（或继承）了一个接口（或抽象类），但没有提供接口（或抽象类）中定义的所有抽象方法的实现。

2. 当尝试调用一个接口（或抽象类）中的抽象方法，但该方法在实际的对象中没有被正确实现时。

要解决`AbstractMethodError`，你需要确保你的类实现了接口或继承了抽象类中所有的抽象方法，并正确地提供了这些方法的实现。

例如，考虑以下的接口和实现：
```java
// 接口
public interface MyInterface {
void myMethod();
}
// 实现类
public class MyClass implements MyInterface {
// 这里没有提供myMethod 的实现
// 编译器会报错，或者在运行时抛出AbstractMethodError
}
```
为了解决这个问题，你需要确保在实现类中提供了所有接口中定义的抽象方法的实现：
```java
public class MyClass implements MyInterface {
@Override
public void myMethod() {
// 提供myMethod 的实现
// ...
}
}
```
如果是继承抽象类的情况，同样需要确保所有抽象方法都有正确的实现。

请检查你的类继承关系，确保每个抽象方法都被正确地实现了。

Java abstract关键字详解1. abstract关键字或抽象类与抽象方法1.1 由来举例1：随着继承层次中一个个新子类的定义，类变得越来越具体，而父类则更一般，更通用。

类的设计应该保证父类和子类能够共享特征。

有时将一个父类设计得非常抽象，以至于它没有具体的实例，这样的类叫做抽象类。

举例2：我们声明一些几何图形类：圆、矩形、三角形类等，发现这些类都有共同特征：求面积、求周长。

那么这些共同特征应该抽取到一个共同父类：几何图形类中。

但是这些方法在父类中又无法给出具体的实现，而是应该交给子类各自具体实现。

那么父类在声明这些方法时，就只有方法签名，没有方法体，我们把没有方法体的方法称为抽象方法。

Java语法规定，包含抽象方法的类必须是抽象类。

1.2 语法格式•抽象方法：被abstract修饰没有方法体的方法。

•抽象类：被abstract修饰的类。

抽象类的语法格式[权限修饰符]abstract class类名{}[权限修饰符]abstract class类名extends父类{}抽象方法的语法格式[其他修饰符]abstract返回值类型方法名([形参列表]);注意：抽象方法没有方法体代码举例：public abstract class Animal {public abstract void eat();}public class Cat extends Animal {public void eat(){System.out.println("小猫吃鱼和猫粮");}}public class CatTest {public static void main(String[] args){// 创建子类对象Cat c =new Cat();// 调用eat方法c.eat();}}此时的方法重写，是子类对父类抽象方法的完成实现，我们将这种方法重写的操作，也叫做实现方法。

1.3 使用说明1.抽象类不能创建对象，如果创建，编译无法通过而报错。

java中abstract的用法在Java中，abstract关键字用于定义抽象类和抽象方法。

1. 抽象类：用abstract修饰的类是抽象类，抽象类不能直接实例化对象，只能被子类继承；抽象类中可以包含抽象方法和非抽象方法，但抽象方法必须在子类中被实现。

例如：```。

abstract class Animal 。

public void eat() 。

System.out.println("Animal is eating.");。

}。

public abstract void makeSound();。

}。

class Dog extends Animal 。

public void makeSound() 。

System.out.println("Woof");。

}。

}。

```。

2. 抽象方法：用abstract修饰的方法是抽象方法，抽象方法没有方法体，只有方法签名，必须在子类中被实现。

子类必须覆盖所有父类的抽象方法。

例如：```。

abstract class Shape 。

abstract void draw();。

}。

class Circle extends Shape 。

void draw() 。

System.out.println("Drawing Circle");。

}。

}。

class Rectangle extends Shape 。

void draw() 。

System.out.println("Drawing Rectangle");。

}。

}。

C++中abstract修饰类的用法1. 概述在C++中，我们经常会听到关于abstract类的概念。

那么，abstract 类到底是什么？它又有什么作用呢？2. 什么是abstract类在C++中，我们可以使用关键字“abstract”来修饰一个类，使其成为一个“abstract类”。

一个abstract类是一种不能被实例化的类，即不能创建它的对象。

abstract类通常用于定义接口和抽象的行为，它的目的是为了让其他类继承并实现它的纯虚函数。

3. abstract类的定义要定义一个abstract类，我们可以在类中声明纯虚函数。

纯虚函数是指在类中声明但没有实现的虚函数。

通过在函数声明后面加上“= 0”来将一个虚函数声明为纯虚函数。

例如：```C++class AbstractClass {public:virtual void pureVirtualFunction() = 0;};```4. abstract类的作用abstract类的作用主要有以下几点：- 定义接口：abstract类定义了一组接口，表示了一种抽象的行为。

其他类可以继承并实现这些接口。

这样一来，我们就可以通过基类指针来调用派生类的函数。

- 特定行为的约束：abstract类可以约束其派生类必须实现某些特定的行为。

这样一来，我们就可以确保派生类都具有相同的接口，从而提高代码的一致性和可维护性。

- 防止实例化：abstract类的对象不能被创建，这可以防止程序员错误地使用该类，从而避免一些潜在的错误。

5. 如何使用abstract类在C++中，我们可以通过继承abstract类并实现其中定义的纯虚函数来使用abstract类。

例如：```C++class ConcreteClass : public AbstractClass {public:void pureVirtualFunction() override {// 实现纯虚函数的具体逻辑}};```在上面的例子中，ConcreteClass继承了AbstractClass，并实现了其中定义的纯虚函数pureVirtualFunction。

有abstract方法的类一定要用abstract
修饰么?
问题：有abstract方法的类一定要用abstract修饰么? 回答：有abstract方法的类一定要用abstract修饰。

一下是一些关于abstract修饰符的用法及规则：
abstract修饰符用来修饰类和成员方法
a：用abstract修饰的类表示抽象类，抽象类位于继承树的抽象层，抽象类不能被实例化。

b：用abstract修饰的方法表示抽象方法,抽象方法没有方法体。

抽象方法用来描述系统具有什么功能，但不提供具体的实现。

abstract的规则：
a：抽象类可以没有抽象方法，但是有抽象方法的类必须定义为抽象类，如果一个子类继承一个抽象类，子类没有实现父类的所有抽象方法，那么子类也要定义为抽象类，否则的话编译会出错的。

b：抽象类没有构造方法，也没有抽象静态方法。

但是可以有非抽象的构造方法
c：抽象类不能被实例化，但是可以创建一个引用变量，类型是一个抽象类，并让它引用非抽象类的子类的一个实例
d：不能用final 修饰符修饰。

abstract java 重写方法在Java中，重写方法是面向对象编程的一个重要概念，它允许子类重新定义从父类继承的方法。

当子类需要改变继承自父类的方法行为时，可以通过重写方法来实现。

下面是一些关于Java中重写方法的相关参考内容：一、概述了解重写方法的基本概念是理解其背后原理的关键。

重写方法是子类定义的一个与父类具有相同方法签名的方法，通过使用@Override注解来标识。

重写方法需要满足以下条件：1. 方法名必须与父类中被重写的方法名一致。

2. 参数列表必须与父类中被重写的方法参数列表一致。

3. 返回类型必须与父类中被重写的方法返回类型相同或是其子类。

4. 访问修饰符不能比父类中被重写的方法更严格。

即如果父类中的方法为public，则子类中重写的方法可以为public或protected，但不能为private。

二、重写方法的作用重写方法的作用是子类可以根据自身的需要来重新定义继承自父类的方法，从而改变其行为。

这对于实现多态有着重要的意义。

通过重写方法，可以使父类的方法在不同的子类对象上具有不同的行为。

三、重写方法的示例下面是一个重写方法的示例，假设有一个父类Animal和一个子类Dog，子类Dog需要改变父类Animal的方法行为：```public abstract class Animal {public abstract void sound();}public class Dog extends Animal {@Overridepublic void sound() {System.out.println("汪汪汪");}}```在上述示例中，Animal类是一个抽象类，其中定义了一个抽象方法sound()。

子类Dog继承自Animal，并重写了sound()方法，并在方法内部输出了"汪汪汪"。

四、注意事项在重写方法时，还需要注意以下几点：1. 重写方法不能比父类方法拥有更宽松的访问权限。

A Web-based Instructional Platform for Constraint-Based GrammarFormalisms and ParsingW.Detmar Meurers Dept.of Linguistics Ohio State University dm@Gerald PennDept.of Computer ScienceUniversity of Torontogpenn@Frank RichterSeminar f¨ur SprachwissenschaftUniversit¨a t T¨ubingenfr@sfs.uni-tuebingen.deAbstractWe propose the creation of a web-basedtraining framework comprising a set oftopics that revolve around the use of fea-ture structures as the core data structurein linguistic theory,its formal foundations,and its use in syntactic processing.1IntroductionFeature structures have been used prolifically at ev-ery level of linguistic theory,and they form the mathematical foundation of our most comprehen-sive and rigorous schools of syntactic theory,includ-ing Lexical-Functional Grammar and Head-driven Phrase Structure Grammar.This data structure is popular because it shares many properties with the first-order terms of classical logic,and in addi-tion provides named access to substructures through paths of features.Often it also includes a type sys-tem reminiscent of the taxonomical classification systems that are widely used in knowledge represen-tation,psychology and the natural sciences.For teaching a subject like computational linguis-tics,which draws on a broad curriculum from many traditional disciplines to audiences with mixed back-grounds themselves,feature-structure-based theo-retical and computational linguistics have three im-portant properties.First,they are a mature disci-pline,in which a great deal of accomplishments have been made over the last20years,spanning from em-pirical and conceptual advances in linguistic theory to its mathematical and computational foundations, to grammar development and efficient processing.Second,they are pervasive as an already existing representation standard for many levels of linguistic study.Third,they are transparent,reducing com-plex theories of grammar to a basic collection of mathematical concepts and algorithms for answer-ing formal questions about those theories.One can address the distinction between descriptions of ob-jects and the objects themselves,the difference be-tween consistency and truth,and what it means for a syntactic theory to be not only elegant but correct in a precise and provable sense.The purpose of this paper is to discuss how these three properties can be cast into an instructional set-ting to arrive at a framework for teaching computa-tional linguistics that highlights the integrated nature and precision with which work in this very hetero-geneous discipline can be presented.In principle, the framework we are proposing is open-ended,in the sense that additional modules should be added by students and other researchers,subject to the de-sign principles given in Section3.We are currently designing three of the core modules for this frame-work:formal foundations,constraint-based gram-mar implementation,and parsing.2Problems of seminar-style coursesThe contents of our core modules are based on a series of previous seminar-style courses,in partic-ular on constraint-based grammar implementation, which also started integrating interactive compo-nents and web-based materials into traditional face-to-face teaching.These are described in detail in Section5.The traditional seminar-style teaching method underlying the courses mentioned thereinhas a number of inherent problems,however.These problems become particularly pressing when topics as diverse as linguistic theory,grammar implemen-tation,parsing,mathematical foundations of linguis-tic theory and feature logics are combined in a single course that is addressed to a mixed audience with varying backgrounds in computer science,knowl-edge representation,artificial intelligence and lin-guistics,in any combination of these subjects. First,the seminar-style teaching format as used in those grammar implementation courses presupposes a fairly coherent audience of linguists with a shared background of linguistic knowledge.Second,since computers are only used as a medium to implement grammars and since the implementation platform is not optimized for web-based training,it is neces-sary that there be a relatively low number of stu-dents per teacher.Third,the theoretical material is in the form of overheads and research papers,which are in electronic form but not easily accessible with-out the accompanying lecture as part of a seminar-style course.Fourth,the background lectures of the courses lack the support of the kind of graphical, interactive visualization that teaching software can in principle offer.Finally,the courses follow a sin-gle path through the materials as determined by the teacher,which the student cannot change according to their specific interests and their prior knowledge. We believe that these shortcomings can be over-come by shifting from a seminar-style to a web-based training format in a way that preserves the positive aspects of successful hands-on courses.On the other hand,to successfully shift from seminar-style to web-based training we believe it is essential to do this based on a scientific understanding of the nature and possibilities of web-based learning.In the next section we therefore embed our work in the context of education and collaborate learning tech-nology research.3Education and collaborative learning technology researchOur perspective on web-based training draws its in-spiration primarily from work in building“learn-ing communities”in education research(Lin et al., 1995;Nonaka,1994),in which:1.a precise context is established to introducetacit knowledge and experience,in this case on subjects in computational linguistics and the traditional disciplines it draws from,2.conflicting perspectives are shared,conceptsare objectified and submitted to a process of justification and arbitration,and3.the concepts are then integrated into the knowl-edge base as modules upon which further in-structional material or grammar implementa-tions can be constructed.We thus intend to provide an environment that teaches students by actively encouraging them to participate in research that extends our collective knowledge in this area.In principle,there are no boundaries to the material that could be included in the evolving framework.We intend to make it avail-able as an open-source standard for grammar de-velopment and instruction in the hope that this will encourage researchers and educators to contribute modules to it,and to use a feature-structure based approach for their own research and courses. Scardamalia and Bereiter(1993)identify seven global characteristics that technologies must have to support this kind of participation:Balance:a distinction between public and private and between individual and group knowledge pro-cesses.That includes free access to others’work,in-cluding implementations of concepts as algorithms or grammars,and opportunities to borrow ideas into their own work that would be prohibitively time-consuming or otherwise advanced to formulate on their own.Such technologies must also encour-age time for personal“reflection and refinement”and anonymous public or private contribution to the knowledge space.The present framework achieves this by providing an open-source setting combined with a web-based instructional tool for self-paced learning and individual design of both the contents and order of the curriculum.Contribution and notification:to prevent ideas from being presented in an insulated structure that discourages questioning,debate,or revision.As dis-cussed in Section4.2,this is achieved by providing extensive linking and annotation of resources using web-compatible metalanguages for integrating mod-ules at the implementational,formal and instruc-tional levels.Source referencing:a means of preserving the boundaries of a contributor’s idea and its credit as well as a history of prior accounts and antecedents to the idea.In the present framework,this is pro-vided by means of a requirements analysis compo-nent that requires contributed modules to identify the contribution by new concepts or resources pro-vided,existing concepts or resources imported for it to work,and an account of existing alternatives with a description of its distinction from them. Storage and retrieval:which places contribu-tions in a“communal context”of related contribu-tions by others to encourage joint work between con-tributors working on problems with significant over-lap.The present framework must organize the pre-sentation of existing modules along several thematic dimensions to accomplish this.Multiple points of entry:for stu-dents/contributors with different backgrounds and levels of experience.Material is made acces-sible in more basic or fundamental modules by projecting the formal content of the subject into a graphically based common-sense domain at which it can be grasped more intuitively(see Section4.3). Accessibility in more advanced modules is provided by links specified in the requirements analysis component to more basic modules that the former rely upon.Coherence-producing mechanisms:feedback to contributors and framework moderators of mod-ules that are“fading”for lack of attention or further development.These can either be reinstated or refor-mulated,moved to a private space of more periph-eral modules,or deleted outright.This is a way of encouraging activity that is productive,and restrict-ing the chance of confusion or information overload. Such a coherence mechanism must exist within this framework.Links to external resources:to situate the justifi-cation and discussion of contributions in a wide con-text.We make use of the web-based training plat-form ILIAS1which is available as open source soft-ware and offers a high degree offlexibility in terms of the integration of internal and external resources.1http://www.ilias.uni-koeln.de/ios/index-e.html 4Integration of the frameworkThe goal of our current work is to transform previ-ous,seminar-style courses and new input into teach-ing materials that arefit for web-based training in the general framework outlined in the previous section. This clearly involves much more than simply refor-matting old teaching materials into web-compatible formats.Instead,it requires an analysis of the con-tents of the courses,the interleaving and hyperlink-ing of the textual materials,and the development of graphical,interactive solutions for presenting and interacting with the content of the material.Since the nature of the textual material as such is familiar (instructional notes,reference guides to major sec-tions with indices,system documentation,annotated system source code,and annotated grammar source code),we use the limited space in this paper to high-light the integrated nature of the approach as well as the web-based training specific issues of hyperlink-ing and visualization.4.1Integration of linguistic and computationalaspectsOur approach is distinguished by its integration of grammars,the parsers that use them and the on-line instructional pared to the LKB system2,which as mentioned in Section5.2has also been used successfully in teaching grammar development,the greater range of formal expres-sive devices available to our parsing system,called TRALE,allows for more readable and compact grammars,which we believe to be of central impor-tance in a teaching context.To illustrate this,we are currently porting the LinGO3English Resource Grammar(ERG)from the LKB(on which the ERG was designed)to the TRALE system.Given the scope of our web-based training frame-work as including an integrated module on parsing, it is also relevant that the TRALE system itself can be relatively compact and transparent at the source-code level since it exploits its close affinity to the underlying Prolog on which it is implemented.This contrasts with the perspective of Copestake et al. (2001),who concede that the LKB is unsuitable for teaching parsing.2/˜aac/lkb.html3/csli/4.2The use of hyperlinksSeveral different varieties of links are distinguished within the course material,giving afirst-class repre-sentation to the transfer of knowledge between the linguistic,computational and mathematical sources that inform this interdisciplinary area.We intend to distinguish the following kinds of links: Conceptual/taxonomical:connecting instances of key concepts and terms used throughout the course material with their definitions and prove-nience;Empirical context:connecting instances of de-sign decisions,algorithms and formal definitions to encyclopedic discussions of their linguistic motiva-tion and empirical significance;Denotational:connecting instances of construc-tional terms and issues within linguistics as well as correctness conditions of algorithms to the mathe-matical definitions that formalize them within the foundations of constraint-based linguistics; Operational:connecting mathematical defini-tions and instances of related linguistic discussions to computational instructional material describing the algorithms used to construct,refute or transform the formal objects representing them in a practical system;Implementational:connecting discussions of al-gorithms to the actual annotated system source code in the TRALE system used to implement them,and mathematical definitions and discussions of linguis-tic constructions to the actual annotated grammar source code used to represent them in a typical im-plementation.The idea behind this classification is that when more course material is added to the web-based training framework we are proposing,the new mate-rial will take into account these distinctions to obtain a conceptually coherent use of hyperlinks through-out the framework.4.3VisualizationOur three core modules make use of a number of graphical user interfaces:a tool for interleaved vi-sualization and interaction with trees and attribute value matrices,one for the presentation of lexical rules and their interaction,an Emacs-based source-level debugger,and a program for the graphical ex-ploration of the formal foundations of typed feature logic.Thefirst two are extensions of tools we al-ready used for our previous courses,and the third is an extension of the ALE source-level debugger,so we here focus on the last,new development.The main goal of the MorphMoulder(MoMo)is to project the formality of its subject,the formal foundations of constraint languages over typed fea-ture structures,onto a graphical level at which it can be grasped more intuitively.4The transparency of this level is essential for providing multiple points of entry(Section3)to this fundamentally impor-tant module.The MoMo tool allows the user to explore the relationship between the two levels of the formal architecture:the descriptions and the el-ements described.To this end,the user works with a graphical interface on a beled di-rected graphs representing feature structures can be constructed on the whiteboard from their basic com-ponents,nodes and arcs.The nodes are depicted as colored balls,which are assigned types,and the arcs are depicted as arrows that may be labeled by feature names.Once a feature structure has been constructed,the user may examine its logical prop-erties.The three main functions of the MoMo tool allow one to check(1)whether a feature structure complies with a given signature,(2)whether a well-formed feature structure satisfies a description or a set of descriptions,and(3)whether a well-formed feature structure is a model of a description or a set of descriptions.In the context of the course,the functions of MoMo thus lead the user from under-standing the well-formedness of feature structures with respect to a signature to an understanding of feature structures in their role as a logical model of a theory.If a student has chosen course modules that include a focus on formal foundations of feature log-ics or feature logics based linguistic theory,thefirst introduction to the subject by MoMo can easily be followed up by a course module with rigorous math-ematical definitions.In constraint-based frameworks,the user declares the primitives of the empirical domain in terms of a type hierarchy with appropriate attributes and at-tribute values.Consider a signature that licenses lists of various birds,which may then be classified according to certain properties.First of all,the sig-4MoMo is written by Ekaterina Ovchinnikova,U.T¨u bingen.nature needs to comprise a type hierarchy and fea-ture appropriateness conditions for lists.Let type listbe an immediate supertype of the types non-empty-list and empty-list in the type hierarchy(henceforthabbreviated as nelist and elist).Let the appropri-ateness conditions declare the attributes HEAD and TAIL appropriate for(objects of)type nelist,the val-ues of TAIL at nelist be of type list,and the valuesof HEAD at type nelist be of type bird(for lists ofbirds).Finally no attributes are appropriate for thetype elist.A typical choice for the interpretation ofthat kind of signature in constraint-based formalismsis the collection of totally well-typed and sort re-solved feature structures.All nodes of totally well-typed and sort resolved feature structures are of amaximally specific type(types with no subtypes);and they have outgoing arcs for all and only thosefeatures that are appropriate to their type,with thefeature values again obeying appropriateness.Oursignature for lists thus declares an ontology of fea-ture structures with nodes of type nelist or elist(butnever of type list),where the former must bear theoutgoing arcs HEAD and TAIL,and the latter have nooutgoing arcs.They signal the end of the list.The HEAD values of non-empty lists must be in the de-notation of the type bird.Figure1illustrates how the MoMo tool can beused to study the relationship between signaturesand the feature structures they license by lettingthe user construct feature structures and interac-tively explore whether particular feature structuresare well-formed according to the signature.To theleft of the whiteboard there are two clickable graph-ics consoles of possible nodes and arcs from whichthe user may choose to draw feature structures.Theconsoles offer nodes of all maximally specific typesand arcs of all attributes that are declared in thesignature.In the present example,parrot,wood-pecker,and canary are the maximally specific sub-types of bird.Each color of edge represents a different attribute,and each color of node represents a different type.The grayed outlines on edges and nodes indicate thatall of the respective edges and nodes in this partic-ular example are licensed by the signature that wasprovided.The HEAD arc originating at the node oftype elist,however,violates the appropriateness con-ditions of the signature.The feature structurede-Figure1:Graphically evaluating well-typedness of feature structures.picted here,therefore,is not well-formed.The sig-nature check thus fails on the given feature structure, as indicated by the red light in the upper function console to the right of the whiteboard. Similarly,MoMo can graphically depict satisfia-bility and modellability of a single description or set of descriptions.To this end,the user may be asked to construct a description that a given feature structure satisfies or models;or she may be asked to construct feature structures that satisfy or model a given de-scription(or set of descriptions).The system will give systematic feedback on the correct or incorrect usage of the syntax of the description language as well as on to which extent a feature structure satis-fies or models descriptions,systematically guiding the user to correct solutions.Figure2shows a successful satisfiability check of a well-formed feature structure.The feature struc-ture is derived from the one in Figure1by re-moving the incorrect HEAD arc and its substructurefrom the elist node.The query,asked in a sepa-rate window,is whether the feature structure satis-fies the constraint(nelist,head:(parrot, color:green),tail:nelist).Since this is the case,the green light on the function console to the right is signaling succeed.If we were to perform model checking of the same feature structure against the same constraint,checking would fail,and MoMo would indicate the nodes of the feature structure that do not satisfy the givenconstraint.Figure2:Graphically evaluating constraint satisfac-tion of feature structures.MoMo’s descriptions are a syntactic parallel to TRALE’s descriptions,thus introducing the student not only to the syntax and semantics of constraint languages but also to the language that will be used for the implementation of grammars later in the course.The close relationship of description lan-guages also facilitates a comparison of their model-theoretic semantics and the truth conditions of gram-mars with the structure and semantics of algorithms that use descriptions for constraint resolution and in parsing.Finally,their common structure allows for a tight network of hyperlinks across the boundaries of different course modules and course topics,linking them to a common source of mathematical,imple-mentational and linguistic indices,which explain the usage of common mathematical concepts across the different areas of application of typed feature struc-tures.5From seminar-style courses toweb-based trainingHaving discussed the ideas driving the web-based teaching platform and exemplified one of the tools, we now return to the courses which have informed our work on the three core modules currently being developed in terms of their content and the use of a web-and implementation environment they make.5.1Grammar implementation in ALEALE5(Carpenter and Penn,1996)is a conserva-tive extension of Prolog based on typed feature structures,with a built-in parser and semantic-head-driven generator.The demand for such a utility was so great when it was beta-released in1992 that it immediately became the subject of early work in graphical front-end development for large constraint-based grammars:first with the Pleuk sys-tem(Calder,1993),then as one of several systems supported by Gertjan van Noord’s HDrug6,followed by an ALE-mode Emacs user interface(Laurens, 1995).It also provided the computational support for one of the veryfirst web-based computational linguistics courses,Colin Matheson’s widely used HPSG Development in ALE7.A follow-up course on computational morphology8,also by Colin Mathe-son,was based on ALE-RA9,a morphological ex-tension of ALE by Tomaz Erjavec.Our current web-based training module is sup-ported by an extension of ALE,called TRALE, that uses a slightly different interpretation of typing found in many linguistic theories and an enhanced constraint language that supports constraints with complex antecedents(Penn,2000).5/˜gpenn/ale.html6http://grid.let.rug.nl/˜vannoord/hdrug/7/projects/ledtools/ale-hpsg/8/projects/ledtools/ale-ra/9http://nl.ijs.si/et/Thesis/ALE-RA/5.2Constraint-based grammarimplementationOver the pastfive years,we have held another course on Constraint-Based Grammar Implementation in a variety of settings,from summer schools to reg-ular curriculum courses.10It offers hands-on ex-perience to linguists interested in the formalization of linguistic knowledge in a constraint-based gram-mar formalism.The course is taught in an interac-tive fashion in a computer laboratory and combines background lectures with practical exercises on how to specify grammars in ConTroll11(G¨o tz and Meur-ers,1997),a processing system for constraint-based grammars intended to process with HPSG theories directly from the form in which they are constructed by linguists.The background lectures of the Constraint-based grammar implementation courses introduce the rel-evant mathematical and computational knowledge and focus on the main ingredients of constraint-based grammars:highly structured lexical represen-tations,constituent structures,and the encoding of well-formedness constraints on grammatical repre-sentations.In the lab,students work on exercises exploring the theoretical concepts covered in the lec-tures.In a later part of the course,they are given the opportunity to undertake individualized gram-mar projects for modeling theoretically and empir-ically significant syntactic constructions of their na-tive language.This course was thefirst hands-on computational syntax course at the European Summer School in Language,Logic,and Information(ESSLLI, 1997:Aix-en-Provence),and was also offered at the LSA Linguistic Institute(1999:University of Illi-nois,Urbana-Champaign)12and the Computational Linguistics and Represented Knowledge(CLaRK) Summer School(1999:Eberhard-Karls Universit¨a t, T¨u bingen)13.Generally regarded as a highly suc-cessful course and teaching method,every subse-quent ESSLLI summer school has offered at least one similar course:Practical HPSG Grammar Engi-neering(1998:Ann Copestake,Dan Flickinger,and 10The courses were taught by E.Hinrichs and D.Meurers.11http://www.sfs.uni-tuebingen.de/controll/12/˜dm/lehre/lsa99/13/˜dm/lehre/clark99/Stephan Oepen)14,Development of large scale LFG grammars:Linguistics,Engineering and Resources (1999:Miriam Butt,Annette Frank,and Jonas Kuhn)15,Grammatical Resources:Logic,Struc-ture,Control(1999:Michael Moortgat and Richard T.Oehrle)16,An Introduction to Grammar Engi-neering using HPSG(2000:Ann Copestake,Rob Malouf)17,Advanced Grammar Engineering using HPSG(2000:Dan Flickinger,Stephan Oepen)18, and An Introduction to Stochastic Attribute-Value Grammars(2001:Rob Malouf,Miles Osborne)19.5.3Introduction to theory-driven CLA further source of material for the core modules of our web-based training framework is the graduate level Introduction to Theory-driven Computational Linguistics at the Ohio State University.20It covers the basic issues of the following topics:finite state automata and transducers,formal language theory, computability and complexity,recognizers/parsers for context free grammars,memoization,and pars-ing with complex categories.The theoretical material is combined with prac-tical exercises in Prolog implementing different as-pects of parsers.At the end of the course,students complete a project consisting of building and testing a grammar fragment for a short English text of their choice.The traditional one-quarter course includes weekly exercises,extensive web-based course mate-rial for students,and a course workbook21as a guide through the theoretical material.5.4Model-theoretic introduction to Syntax Our approach to teaching the fundamentals of math-ematical theories through graphical metaphors in the context of syntax derives from our experience with this method in teaching Syntax I(HPSG)at the Eberhard-Karls Universit¨a t T¨u bingen in1998, 14http://www.coli.uni-sb.de/esslli/Seiten/Oepen.html15http://www.let.uu.nl/esslli/Courses/butt.html16http://www.let.uu.nl/esslli/Courses/moortgat-oehrle.html 17/˜esslli/notes/copestake.html18/˜esslli/notes/oepen.html19http://odur.let.rug.nl/˜malouf/esslli01/20The course was taught by D.Meurers;see http://ling.osu. edu/˜dm/2001/winter/684.01/21This workbook is based,with kind permission from the authors,on the module workbook for“Techniques in Natural Language Processing1”by Chris Mellish,Pete Whitelock and Graeme Ritchie,1994,Dept.of AI,University of Edinburgh.1999and2001.22In these seminars,which did not presuppose any prior knowledge of model-theoretic methods in logic,the mathematical foundations of feature logic were introduced by intuitive means but with as much precision as possible without strict for-malization.An introduction to a standardized ver-sion of the logical description language of HPSG was accompanied with problem sets that required the students to construct three-dimensional feature structure models(made of styrofoam and wires)of descriptions and sets of descriptions.The informal but very concrete understanding of the relationship between a theory cast in a constraint language and its feature structure models had a very positive result on students’ability to grasp and build working analyses of unseen constructions compared to the results of the more traditional method of teaching constraint-based syntax used in previous years.At the same time,the teaching method successfully used an ap-peal to prior world knowledge rather than unfamiliar mathematical notation in order to make the students familiar with the basic concepts of constraint satis-faction and truth in feature logics.6Summary and OutlookThe interdisciplinary nature of computational lin-guistics and the diverse backgrounds of the student audience makes it particularly attractive to teach a subject like constraint-based grammar formalisms and parsing using a web-based instructional plat-form which integrates formal and computational foundations,linguistic theory,and grammar im-plementation.We discussed several seminar-style courses which have informed our proposal in terms of content,highlighted the problems of the tradi-tional face-to-face teaching,and described our en-vironment of web-based teaching materials plus im-plementational support.We argued that a web-based training framework for the topic can be organized around feature structures as a central data structure in formal foundations,linguistics and implementa-tion.We outlined the educational and collaborative learning background in which an informed proposal on web-based training must be embedded and used the newly developed tool MoMo as an illustration 22The courses were taught by F.Richter and M.Sailer;see http://www.sfs.uni-tuebingen.de/˜fr/teaching/of how we envisage projecting the formal content of the subject into a graphically based common-sense domain in which it can be grasped more intuitively. The three core modules on formal founda-tions,constraint-based grammar implementation, and parsing will be completed and made publicly available at the end of2003.The joint project is funded by the German Federal Ministry for Re-search Technology(BMBF)as part of the consor-tium Media-intensive teaching modules in the com-putational linguistics curriculum(MiLCA).23 ReferencesJ.Calder.1993.Graphical interaction with constraint-based grammars.In Proceedings of PACLING’93, pages160–168,Vancouver,British Columbia.B.Carpenter and piling typedattribute-value logic grammars.In H.Bunt and M.Tomita,editors,Recent Advances in Parsing Tech-nologies,pages145–168.Kluwer,Dordrecht.A.Copestake,J.Carroll,D.Flickinger,R.Malouf,anding an open-source unification-based system for CL/NLP teaching.In Proceedings of the EACL/ACL Workshop on Sharing Tools and Re-sources for Research and Education,pages35–38. T.G¨o tz and W.D.Meurers.1997.The ConTroll system as large grammar development platform.In Proceed-ings of the EACL/ACL Workshop on Computational Environments for Grammar Development and Linguis-tic Engineering,pages38–45./˜dm/ papers/envgram.html.urens.1995.An Emacs user interface for ALE.Technical Report CSS-IS TR95-07,School of Com-puting Science,Simon Fraser University.X.Lin,J.D.Bransford,and C.E.Hmelo.1995.Instruc-tional design and development of learning communi-ties:an invitation to cational Technol-ogy,35(5):53–63.I.Nonaka.1994.A dynamic theory of organizationalknowledge anizational Science,5(1). G.Penn.2000.Applying Constraint Handling Rulesto HPSG.In Proceedings of the Workshop on Rule-Based Constraint Reasoning and Programming,CL 2000.M.Scardamalia and C.Bereiter.1993.Technologies for knowledge-building munications of the ACM,36(5):37–41.23http://milca.sfs.uni-tuebingen.de/A4/HomePage/top.html。

Java中的abstract方法和abstract类的问题当知道一个类的子类将不同的实现某个方法时，把该类声明为抽象类很有用，可以共用相同的父类方法，不必再定义。

抽象类和抽象方法的关系:含有抽象方法的类一定是抽象类，抽象类里不一定含有抽象方法。

抽象类存在的意义是用来被继承的。

一个类继承了一个抽象类，必须实现抽象类里面所有的抽象方法，否则，此类也是抽象类。

abstract修饰符用来修饰类和成员方法1：用abstract修饰的类表示抽象类，抽象类位于继承树的抽象层，抽象类不能被实例化。

2：用abstract修饰的方法表示抽象方法，抽象方法没有方法体。

抽象方法用来描述系统具有什么功能，但不提供具体的实现。

abstract 规则:1：抽象类可以没有抽象方法，但是有抽象方法的类必须定义为抽象类，如果一个子类继承一个抽象类，子类没有实现父类的所有抽象方法，那么子类也要定义为抽象类，否则的话编译会出错的。

2：抽象类没有构造方法，也没有抽象静态方法。

但是可以有非抽象的构造方法3：抽象类不能被实例化，但是可以创建一个弓I用变量，类型是一个抽象类，并让它弓I用非抽象类的子类的一个实例4：不能用final修饰符修饰Qjava里面有抽象类么？和接口的区别是什么？A:java中有抽象类，用关键字abstract修饰。

以下是我对这个问题的看法。

首先，从语法上讲，抽象类是一个类，根据java的单继承体系。

如果它有子类，那么它的子类只能继承它。

java允许实现多个接口。

所以一个类可以实现多个接口抽象类里面可以定义各种类型和访问权限的变量（就像普通类一样），也可以定义各种访问权限的方法（就像普通类一样）。

但是接口不可以。

在接口里面定义的方法默认就是public absti-act的，变量默认就是public staticfinal的。

（不管你有没有加权限控制符，不加，默认就是这些权限；加错了，权限缩小7,那么就会报错）其次，从意义上讲，如果继承一个抽象类，那么抽象类和它的子类就有父子关系，即有类的层次关系（这关系到类的设计问题）。

Python中的abstractmethod方法是面向对象编程中非常重要的概念之一。

它允许开发者定义抽象基类（Abstract Base Classes），并在其中声明抽象方法，这些方法需要在子类中进行实现。

通过abstractmethod方法，Python提供了一种强大的方式来约束和规范子类的行为，从而提高代码的可维护性和可扩展性。

在Python中，我们可以使用abc模块来定义抽象基类，并通过abstractmethod装饰器来声明抽象方法。

这使得在使用和维护大型代码库时更加方便和安全。

通过对abstractmethod方法的深入理解，开发者可以更好地利用Python强大的面向对象编程特性，提高代码的质量和可读性。

在本文中，我将从基本概念、使用方法、实际应用和个人观点等方面，对abstractmethod方法进行全面评估和探讨。

通过以从简到繁的方式展开讲解，希望能够帮助您更加深入地理解abstractmethod方法的重要性和灵活运用。

1. 基础概念在面向对象编程中，抽象类和抽象方法是非常重要的概念。

抽象类是指不能被实例化的类，其中的抽象方法需要在子类中进行实现。

而abstractmethod方法的作用就是用来声明抽象方法，从而使得子类必须实现这些方法才能正常运行。

这种强制实现的机制可以帮助开发者规范代码结构，提高代码的可维护性和可读性。

2. 使用方法通过在抽象基类中使用abstractmethod装饰器来声明抽象方法，可以很容易地定义出清晰的接口和规范。

子类必须实现这些抽象方法，否则在实例化时会抛出TypeError异常。

这种方式可以有效地减少代码中的错误和不一致性，提高代码的健壮性和可靠性。

3. 实际应用在实际项目开发中，abstractmethod方法可以被广泛应用。

在设计框架和库时，可以使用abstractmethod方法定义接口和规范，从而规范用户的使用行为；在团队协作时，可以使用abstractmethod方法约束团队成员的代码实现，提高代码的统一性和规范性；在单元测试时，可以使用abstractmethod方法确保代码的覆盖率和正确性。

Java 48个关键字总结珍藏版1.abstract Java 关键字abstract 关键字可以修改类或方法。

abstract 类可以扩展（增加子类），但不能直接实例化。

abstract 方法不在声明它的类中实现，但必须在某个子类中重写。

示例public abstract class MyClass{}public abstract String myMethod();注释采用abstract 方法的类本来就是抽象类，并且必须声明为abstract。

abstract 类不能实例化。

仅当abstract 类的子类实现其超类的所有abstract 方法时，才能实例化abstract 类的子类。

这种类称为具体类，以区别于abstract 类。

如果abstract 类的子类没有实现其超类的所有abstract 方法，该子类也是abstract 类。

abstract 关键字不能应用于static、private 或final 方法，因为这些方法不能被重写，因此，不能在子类中实现。

final 类的方法都不能是abstract，因为final 类不能有子类。

2.boolean 变量的值可以是true 或false。

示例boolean valid = true;if (valid){<statement>}注释boolean 变量只能以true 或false 作为值。

boolean 不能与数字类型相互转换。

包含boolean 操作数的表达式只能包含boolean 操作数。

Boolean 类是boolean 原始类型的包装对象类3.break 关键字用于提前退出for、while 或do 循环，或者在switch 语句中用来结束case 块。

示例for (i=0; i<max; i++){if (<loop finished early>){break;}}int type = <some value>;switch (type){case 1:<statement>break;case 2:<statement>break;default:<statement>}注释break 总是退出最深层的while、for、do 或switch 语句。

java abstract方法在Java中，抽象方法是没有具体实现的方法。

它只有方法签名，没有方法体。

抽象方法必须声明在抽象类或者接口中，并且子类或实现类必须实现这些抽象方法。

要声明一个抽象方法，需要在方法声明前面加上关键字"abstract"。

例如：```javapublic abstract void methodName();```注意以下几点：1. 抽象方法不能被标记为private、final、static或native。

2. 如果一个类包含了抽象方法，那么这个类必须被声明为抽象类。

3. 子类继承抽象类时，必须实现其所有的抽象方法，除非子类自己也是抽象类。

4. 接口中的方法默认都是抽象方法，不需要使用abstract关键字来声明。

下面是一个简单的示例，展示了如何定义和使用抽象方法：```javaabstract class Animal {public abstract void sound();}class Dog extends Animal {public void sound() {System.out.println("汪汪");}}public class Main {public static void main(String[] args) {Dog dog = new Dog();dog.sound(); // 输出：汪汪}}```在上述示例中，Animal是一个抽象类，其中包含了一个抽象方法sound()。

Dog类继承自Animal类并实现了sound()方法，输出了"汪汪"。

abstract关键字用法
abstract关键字用法有以下几种：
1. 抽象类的声明：在类的声明前加上abstract，表示该类是抽象类，不能直接实例化，只能被继承。

2. 抽象方法的声明：在方法的声明前加上abstract，表示该方法是抽象方法，没有具体的实现，需要子类去实现。

抽象方法没有方法体，用分号代替。

3. 抽象属性的声明：在成员变量的声明前加上abstract，表示该成员变量是抽象属性，没有具体的实现，需要子类去实现。

4. 接口的声明：接口中的所有方法默认都是抽象方法，所有成员变量默认都是public、static、final类型，可以不用声明为abstract。

5. 抽象类的继承：一个非抽象类可以继承一个抽象类，但必须实现该抽象类的所有抽象方法。

总的来说，abstract关键字的作用是定义抽象类、抽象方法或抽象属性，通过继承和实现来完成具体的操作。

抽象类英语作文Abstract ClassAbstract class is a concept in object-oriented programming that allows us to create a class which cannotbe instantiated on its own. It serves as a base for other classes to inherit and provides a common interface for all the derived classes.The main purpose of an abstract class is to define a blueprint for other classes to follow. It contains abstract methods, which are methods with no implementation, and concrete methods, which have an implementation. Theabstract methods must be implemented by the derived classes, while the concrete methods can be used as they are or overridden.One key feature of an abstract class is that it cannotbe instantiated. This means we cannot create an object ofan abstract class directly. Instead, we need to create a subclass that extends the abstract class and theninstantiate the subclass.Another important aspect of abstract class is that itcan have member variables just like a regular class. These member variables can be inherited by the subclasses andused as per their requirements.In Java, we use the "abstract" keyword to declare an abstract class. Any class that contains at least oneabstract method must be declared as an abstract class. We also use the "extends" keyword to create a subclass that inherits from the abstract class.In conclusion, abstract class is a powerful tool inobject-oriented programming that allows us to define a common interface for a group of related classes. It helpsin achieving abstraction and reusability in our code, making it easier to maintain and extend our software system.抽象类抽象类是面向对象编程中的一个概念，允许我们创建一个不能单独实例化的类。