scala 字段覆盖_Scala中的字段覆盖

ゝ一世哀愁。 2023-03-05 09:55 28阅读 0赞

scala 字段覆盖

## Scala字段覆盖 **(**Scala field overriding**)** ##

**Overriding** is the concept in which the child class is allowed to redefine the members of the parent class. Both methods and variables/ fields can be overridden in object-oriented programming. In Scala as well both methods and Fields can be overridden but overriding of fields has some restrictions on implementation.

**覆盖**是允许子类重新定义父类成员的概念。 在面向对象的编程中，方法和变量/字段都可以被覆盖。 在Scala中，方法和字段都可以被覆盖，但是字段的覆盖对实现有一些限制。

### Scala中的覆盖字段 **(**Overriding fields in Scala**)** ###

For **overriding fields in Scala**, some rules must be kept in mind to avoid errors that arise while implementing this concept,

为了**覆盖Scala中的字段，**必须牢记一些规则，以避免在实施此概念时出现错误，

1.  The use of **override keyword** is necessary to implement the concept **field overriding**. If you missed the keyword an error will be prompted and execution of the code will be stopped.
    
    要实现概念**字段重写，**必须使用**override关键字** 。 如果您错过了关键字，将提示错误并停止执行代码。
2.  Only fields that are defined using the [val keyboard][] for defining fields in both parent class and child class can be overridden.
    
    只能覆盖使用[val键盘][val keyboard]定义的用于定义父类和子类中字段的字段。
3.  Fields that are defined using the [var keyword][] cannot be overridden as they are editable ( that is both read and write operations are allowed on the variable) anywhere in the class.
    
    使用[var关键字][var keyword]定义的字段不能被覆盖，因为它们在类中的任何位置都是可编辑的(即，允许对变量进行读写操作)。

Here are some programs that show the **implementation of field overriding and Scala**.

这里有一些程序显示了**字段覆盖和Scala的实现** 。

**1) Python program without override keyword**

**1)没有替代关键字的Python程序**

This program will show what will be the output if override keyword is not used?

如果不使用override关键字，该程序将显示什么输出？

class animal{
          
        val voice = "animal's voice" 
    }  
    
    class dog extends animal{
          
       val voice = "Dog bark's...!"  
        def says(){
          
            println(voice)  
        }  
    }  
    
    class cat extends animal{
        
        val voice = "cat meow's...!";
        def says(){
          
            println(voice)  
        } 
    }
    
    object MainObject{
          
        def main(args:Array[String]){
          
            var ani = new dog()  
            ani.says()  
        }  
    }

**Output**

**输出量**

error: overriding value voice in class animal of type String;
     value voice needs `override' modifier
       val voice = "Dog bark's...!"
           ^
    error: overriding value voice in class animal of type String;
     value voice needs `override' modifier
        val voice = "cat meow's...!";
            ^
    two errors found

**2) Python program with override keyword**

**2)具有override关键字的Python程序**

This program will show what will be the output if override keyword is used?

该程序将显示如果使用override关键字将输出什么？

class animal{
          
        val voice = "animal's voice"
    }  
    
    class dog extends animal{
          
       override val voice = "Dog bark's...!"  
        def says(){
          
            println(voice)  
        }  
    }  
    
    class cat extends animal{
        
        override val voice = "Cat meow's...!";
        def says(){
          
            println(voice)  
        } 
    }
    
    object MainObject{
          
        def main(args:Array[String]){
          
            var ani = new dog()  
            ani.says()  
            var ani2 = new cat()
            ani2.says()
        }  
    }

**Output**

**输出量**

Dog bark's...!
    Cat meow's...!

**3) Python program with var keyword**

**3)使用var关键字的Python程序**

This program will show what will be the output if var keyword is used?

该程序将显示如果使用var关键字将输出什么？

class animal{
          
        var voice = "animal's voice"
    }  
    
    class dog extends animal{
          
       override var voice = "Dog bark's...!"  
        def says(){
          
            println(voice)  
        }  
    }
    
    class cat extends animal{
        
        override var voice = "Cat meow's...!";
        def says(){
          
            println(voice)  
        } 
    }
    
    object MainObject{
          
        def main(args:Array[String]){
          
            var ani = new dog()  
            ani.says()  
            var ani2 = new cat()
            ani2.says()
        }  
    }

**Output**

**输出量**

error: overriding variable voice in class animal of type String;
     variable voice cannot override a mutable variable
       override var voice = "Dog bark's...!"
                    ^
    error: overriding variable voice in class animal of type String;
     variable voice cannot override a mutable variable
        override var voice = "Cat meow's...!";
                     ^
    two errors found

> 翻译自: [https://www.includehelp.com/scala/field-overriding-in-scala.aspx][https_www.includehelp.com_scala_field-overriding-in-scala.aspx]

scala 字段覆盖

[val keyboard]: https://www.includehelp.com/scala/val-keyword-with-example-in-scala.aspx
[var keyword]: https://www.includehelp.com/scala/var-keyword-with-example-in-scala.aspx
[https_www.includehelp.com_scala_field-overriding-in-scala.aspx]: https://www.includehelp.com/scala/field-overriding-in-scala.aspx