How String class is thread safe in java?

Question

public class ThreadString extends Thread {
    String str = "ABC";

    public void run() {
        str = "abc";
    }
}

if threads are accessing above run method, reference to the "ABC" now pointing to "abc" how it will works internally?

Answer 1

Strings in Java are immutable. You aren't modifying the String, you're just pointing to another value. From that point of view, it's thread safe - str is either "ABC" or "abc", it can't be something invalid or illegal.