What is the Java equivalent of a Scala object?

Question

In Scala, we can write

object Foo { def bar = {} }

How is this implemented by the compiler? I am able to call Foo.bar(); from Java but new Foo(); from Java gives the error cannot find symbol symbol: constructor Foo()

• Does the JVM support singletons natively?
• Is it possible to have a class in Java that does not have a constructor?

Note: here is the code output by scalac -print

package <empty> {
  final class Foo extends java.lang.Object with ScalaObject {
    def bar(): Unit = ();
    def this(): object Foo = {
      Foo.super.this();
      ()
    }
  }
}

Answer 1

When compiling your code, Scala compiler produces an equivalent of the following Java code:

public final class Foo {
    private Foo() {} // Actually, Foo doesn't have constructor at all
                     // It can be represented in bytecode, 
                     // but it cannot be represented in Java language

    public static final void bar() {
        Foo$.MODULE$.bar();
    }
}

public final class Foo$ implements ScalaObject {
    public static final Foo$ MODULE$;
    static {
        new Foo$();
    }
    private Foo$() { MODULE$ = this; }
    public final void bar() {
        // actual implementation of bar()
    }
}

Here Foo$ is an actual implementation of a singleton, whereas Foo provides a static method for interaction with Java.