pointers - Go Programming - bypassing access privileges using pointers

Question

Let's say I have the following hierarchy for my project:

fragment/fragment.go
main.go

And in the fragment.go I have the following code, with one getter and no setter:

package fragment

type Fragment struct {
    number int64   // private variable - lower case
}

func (f *Fragment) GetNumber() *int64 {
    return &f.number
}

And in the main.go I create a Fragment and try to change Fragment.number without a setter:

package main

import (
    "fmt"
    "myproject/fragment"
)

func main() {
    f := new(fragment.Fragment)

    fmt.Println(*f.GetNumber()) // prints 0

    //f.number = 8 // error - number is private

    p := f.GetNumber()
    *p = 4                      // works. Now f.number is 4
    fmt.Println(*f.GetNumber()) // prints 4
}

So by using the pointer, I changed the private variable outside of the fragment package. I understand that in for example C, pointers help to avoid copying large struct/arrays and they are supposed to enable you to change whatever they're pointing to. But I don't quite understand how they are supposed to work with private variables.

So my questions are:

1. Shouldn't the private variables stay private, no matter how they are accessed?
2. How is this compared to other languages such as C++/Java? Is it the case there too, that private variables can be changed using pointers outside of the class?

My Background: I know a bit C/C++, rather fluent in Python and new to Go. I learn programming as a hobby so don't know much about technical things happening behind the scenes.