Question

I am start working on existing Scala and Akka project. I say Scala classes, some fields making them as private and providing getter and setter methods in different way. why like that you can make it as public also right.

I say in my project

Why this way:

class Person() {  
 // Private age variable, renamed to _age 
 private var _age = 0 
 var name = "" 

 // Getter 
 def age = _age 

 // Setter 
 def age_= (value:Int):Unit = _age = value 
}

So you can get same feeling like public:

person.age = 99

Why not this simple way?

class Person() {  
 var name = "" 
 var age = 0 
} 

// Instantiate a person object 
person = new Person() 

// Print the object's age and name properties 
println(person.age)  
println(person.name) 


// Set the properties to different values 
person.age = 34  
person.name = "Dustin Martin"

Answer 1

对于这个特定情况，没有理由。如果它来自一个真实的项目，这可能是由一个不了解其观点的人从一个例子中复制而来的。您只想在Scala执行 other 时使用显式的getter / setter方法，而不仅仅是改变私有变量。

（正如Dima的答案正确地说，你应该首先尝试不要var。）

Answer 2

两种方式都很糟糕。避免在类中使用可变成员，除非您在特定情况下有特定的理由使用它们。

 case class Person(name: String, age: Int) {
   def rename(newName: String) = copy(newName)
   def grow(numYears: Int) = copy(age = this.age + numYears)
 }

 val teen = Person("John", 15) 
 val adult = teen.grow(5)

等

Answer 3

Accessing and mutating data members of the class directly is the bad idea. Thats why its a good practice to to declare the mutable data member as private and provide public getter and setter to access and mutate it (data member).

1) Its a good practice because access to the mutable state should be controlled

2) You can add some validation in the getter and setter like this

for getter

def age = if (_age >= 18) _age else throw new Exception("minor")

for setter

def age_=(age: Int) = if (age < 18) throw new Exception("minor") else _age = age

Answer 4

它主要谈论封装。根据Object world， 你应该只通过一个动作来实现一个状态 。例如，我不能在没有推动加速器的情况下用我的车达到100kmph。因此通过加速（动作）实现车速100kmph（状态）仅。

scala风格的getter和setter可能会给你带来很少的混淆，但这就是所有的语法混淆（在最初几天）但 Scala 没有妥协封装 即可。你仍然可以使用java风格的getter和setters，如下所示

$input = [];
$query = "SELECT * FROM `categories`";
$result = mysql_query($query);
while($row = mysql_fetch_array($result)){
   $input[] = $row;
}

$result = appendChildren($input);

foreach($result as $row)
{ 
   // open <li> tag
   if(count($row["children"]) > 0)
   {
      foreach($children as $child)
          // add ordered list
   }
   // close <li> tag
}

getter和setter的Java Bean样式将动态生成。但@BeanProperty用于Java互操作性。For more info

Scala - why private member then

4 个答案: