When private doesn’t quite mean what you think it means, Java edition

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Private access in Java is about regulating scope at compile time, not enforcing security measures at runtime. When something is declared private in a particular Java class, it is not accessible to other Java classes.

Well, we should qualify that regarding nested classes, and we will. Consider this toy example of a class:

package com.example;

public class ToyExample {
    
    private int counter = 0;
    
}

Then a ToyExample instance’s counter can’t be accessed by any other class.

package com.example;

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

class ToyExampleTest {
    
    @Test
    void testCounter() {
        ToyExample instance = new ToyExample();
        instance.counter = 1; // ERROR!!! This will not compile
    }

}

But whatever is private in an inner or nested static class is still accessible in the containing class.

package draft.com.example;

public class ToyExample {

    private int counter = 0;

    public static void main(String[] args) {
        NestedClass instance = new NestedClass();
        instance.innerCounter++; // Not a syntax error
    }
    
    static class NestedClass {
        
        private int innerCounter = 0…