Go's sync.Once with Java 17

LocalOnceDemo.java

package wb.java17;

import java.util.function.Supplier;

public class LocalOnceDemo {

    public static void main(String[] args) {
        System.out.println(answer());
        System.out.println(answer());
    }

    static int answer() {
        class Once {
            private static Supplier<?> compute;

            static class Inner { private static final Object theAnswer = compute.get(); }

            public static <T> T Do(Supplier<T> compute, Class<T> clazz) {
                Once.compute = compute;
                return clazz.cast(Inner.theAnswer);
            }
        }
        return Once.Do(LocalOnceDemo::compute, Integer.class);
    }

    static int compute() {
        System.out.println("compute");
        return 42;
    }
}