How does access modifiers (public, protected, default, private) behave in multithreaded code?

In Java, access modifiers can impact the visibility and accessibility of class members, which becomes particularly relevant in a multithreaded context. Here’s a breakdown of how each modifier behaves:

Public: Members declared as public are accessible from any other class, whether it's in the same package or different packages. This is the most permissive access level. However, access should be done carefully in a multithreaded environment to avoid inconsistent states.
Protected: Protected members are accessible within the same package and also by subclasses in different packages. They provide a balance between access and encapsulation, but care must be taken when subclasses may contain thread interaction that could lead to race conditions.
Default (Package-Private): If no modifier is specified, members are accessible only within classes in the same package. This can help limit the scope of access, making it easier to manage interactions in multithreading.
Private: Private members are only accessible within the class they are declared in. This offers the highest level of encapsulation, making it easier to manage shared state in multithreaded environments. Access to shared private state usually requires synchronized methods or blocks.

Here’s a simple example demonstrating how these access modifiers might be applied in a multithreaded scenario:


        class Example {
            private int count = 0;

            public synchronized void increment() {
                count++;
            }

            public int getCount() {
                return count;
            }
        }

        public class Main {
            public static void main(String[] args) {
                Example example = new Example();
                Runnable task = () -> {
                    for (int i = 0; i < 1000; i++) {
                        example.increment();
                    }
                };

                Thread thread1 = new Thread(task);
                Thread thread2 = new Thread(task);

                thread1.start();
                thread2.start();

                try {
                    thread1.join();
                    thread2.join();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                System.out.println("Final count: " + example.getCount());
            }
        }

In this example, the increment() method is synchronized to ensure that the shared state (count) is consistently updated across multiple threads.

public protected default private multithreading access modifiers concurrency in Java

How does access modifiers (public, protected, default, private) behave in multithreaded code?

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How does access modifiers (public, protected, default, private) behave in multithreaded code?

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