method visibility

method  access modifier

1. Object-private scope 只能this
2. Private  this和其他instances
3. Protected  subclasses 
4. Package  this package scope 相当于java的默认friendly
5. More package-level control
6. Public

1　　most restrictive access is to mark a method as “object-private.”

private[this] def isFoo = true

只对current instance available，Other instances of the same class不能access，即使是在同一个class中。

2　　 available to (a) the current class and (b) other instances of the current class，not available to subclasses

和java 的private一样。

3　　available to subclasses

Java，protected methods can be accessed by other classes in the same package, but not in Scala.

4　　private[packageName] syntax--available to all members of the current package

5　　 fine-grained level of access control：

6　　any class can access

//example for fine-grained control level

package com.acme.coolapp.model {
    class Foo {
        private[model] def doX {}
        private[coolapp] def doY {}
        private[acme] def doZ {}
    }
}

import com.acme.coolapp.model._

package com.acme.coolapp.view {
    class Bar {
        val f = new Foo
        f.doX  // won't compile
        f.doY
        f.doZ
    }
}

package com.acme.common {
    class Bar {
        val f = new Foo
        f.doX  // won't compile
        f.doY  // won't compile
        f.doZ
    }
}

 REFERENCE https://alvinalexander.com/scala/how-to-control-scala-method-scope-object-private-package