Scala Abstract class

Scala Abstract class

Abstract class

Scala defines abstract classes

1. An abstract class cannot be instantiated.

2. A class that contains an abstract method must be defined as an abstract class, that is, using the abstract keyword to define a class

3. Abstract classes can have abstract types (type)

4. Abstract classes can contain abstract fields

5. ...............................
   

The following is a simple definition of an abstract class

/** * * @param name * @param age */abstract Class staff (name:string, age:int) {/** * abstract field in Scala */var _departme   nt:string def department:string = _department def department_= (newvalue:string): Unit = _department = NewValue/**  * The definition parameter is empty, the return value is the abstract method of unit */def doWork (): Unit/** * Abstract method * @param value * @return */def Echo (value:string): String def work () = {println (' start work ') This.dowork () println ("Work End")}

The following is the inheritance and implementation of the parent class above

/** *  only the primary constructor of a subclass can call the parent class's main constructor  *  @param  name *  @param  age * @ Param address */class normalstaff (name: string, age: int, address:  String)  extends staff (name: string, age: int)  {  override var  _department: string = _  def this (Name: string, age: int)  {    this (name, age,  "Unknow");  }  //  implementing the abstract method of the parent class   override def dowork ():  unit = {    println ("I ' m  Doing some job ")   }  /**   *  abstract methods    *  You must use the Override keyword    *  @param  value   *  @return    */   override def echo (value: string):  string = value  override  def tostring =  "Normalstaff [name="  + this.name +  ", age="  + this.age +      ", department="  + this._department +  "]"}

Abstract types of abstract classes

Class Foodabstract class Animal {type Suitablefood <: Food def Eat (Food:suitablefood)}class Grass extends Foodclass Cow extends Animal {type Suitablefood = Grass override Def eat (Food:grass) {}}

Use the Type keyword to define an abstract type, type Suitablefood, and indicate that his upper bound is food.

Abstract class Abstract {type T def transform (x:t): t Val initial:t var current:t}class concrete extends Abstract {Override type T = String override def transform (x:t): t = x + x//In Java This is the final variable, so you must initialize the assignment override Val initial: T = "string"//in Java This private type variable, in Scala you can yoga the underscore value override var current:t = _}

In this example, the Type keyword is used to define the abstract type T, in the implementation class to overwrite and indicate the concrete type of the abstract type, override type T = String:

Abstract fields of abstract classes

Abstract class Abstract {type T def transform (x:t): t val initial:t var current:t}

In this case, the member variables defined with Val and Var are not initialized, and after Scala's compiled bytecode, it is an abstract method in the Java class after compilation.

C:\workspace5-gitosc\scala-sample\out\production\scala-sample\com\usoft3>javap-p Abstract.classCompiled from "  Test.scala "public abstract class Com.usoft3.Abstract {public abstract Java.lang.Object transform (java.lang.Object);  Public abstract Java.lang.Object initial ();  Public abstract Java.lang.Object current ();  public abstract void Current_$eq (Java.lang.Object); public com.usoft3.Abstract ();}

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Val Initial:tvar current:t

The abstract approach to the corresponding Java class is to

Public abstract Java.lang.Object Initial ();p ublic abstract Java.lang.Object current ();

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Scala Abstract class