How does a Java anonymous inner class access member variables of an outer class?

Anonymous inner classes access outer class member variables, including private variables, through their this keyword, and access outer class member variables through this just as if the anonymous inner class itself declared these variables.

Java's mechanism for anonymous inner classes to access external class member variables

Anonymous inner classes are inner classes without names, usually used to create one-time class to use. An anonymous inner class can access member variables of its outer class, including private variables.

Access mechanism:

The anonymous inner class accesses the member variables of the outer class through its this keyword. this keyword points to an instance of an anonymous inner class, which is actually an instance of its outer class. Therefore, this can directly access the member variables of the outer class, just as if the anonymous inner class itself had declared these variables.

Practical case:

We create an external class with private member variable secretOuterClass class, and create an Anonymous inner class to access this variable:

public class OuterClass类 {
    private int secret = 42;

    public static void main(String[] args) {
        OuterClass类 outer = new OuterClass类();
        Runnable r = new Runnable() {
            @Override
            public void run() {
                System.out.println("匿名内部类的 secret：" + this.secret);
            }
        };
        r.run();
    }
}

When you run this program, it will output: "Anonymous inner class secret: 42". This is because the anonymous inner class can access the private variables secret of the outer class OuterClass class through this.

It should be noted that:

• The anonymous inner class can only access the member variables of the outer class, but not its methods.
• If the member variable of the outer class is final, the anonymous inner class can only read but not modify the variable.

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