Why can java lambda expressions reference parent class members using "this" keyword whereas anonymous classes can not?

Question

In the following class:

public class ThreadTest {

    public static String name = "Member Accessed";
    
    
    public void run() {
    
        // Anonymous class
        Runnable r1 = new Runnable() { 
        
            @Override
            public void run() {
                System.out.println("Using Anonymous class, referencing this.name " + this.name);
            }
        };
        
        // lambda expression
        Runnable r2 = () -> {
            System.out.println("Using Lambda Expression, referencing this.name " + this.name);
        };
        
        new Thread(r1).start();
        new Thread(r2).start();
    }


    public static void main(String[] args) {
    
        ThreadTest tt = new ThreadTest();
        tt.run();

    }
}

Why can the lambda expression access this.name, whereas the anonymous class can not? I understand that for the anonymous class, this references the anonymous class scope, and name doesn't exist there. However, the lambda expression is basically an anonymous method that belongs to an anonymous class that implements an interface. So, technically this should also reference the anonymous class for the lambda expression.. But somehow, this manages to reference name.

Why is this the case?

Answer 1

First of all, fix this as long as you refer to the instance and not the class variable:

public String name = "Member Accessed";

Though each lambda expression can be expressed as an anonymous class, their bytecodes differ, as Eliott Frisch said. I am not knowledgeable enough to provide more details, but there is a very interesting reading from Brian Goetz I can refer you to. Sadly, the script is accessible only through this answer as long as the original link is no longer active: Lambda Translation Strategy.

---

Anyway, the anonymous class can point out the instance variable of the outer class by specifying the class name using this.

Runnable r1 = new Runnable() {

    @Override
    public void run() {
        System.out.println("Using Anonymous class: " + ThreadTest.this.name);
    }
};