no enclosing instance of type... in scope
Solution 1
Inner
is an inner class. It can only be created when there is an enclosing instance of the class containing the Inner
class definition.
However, you've created a static
nested class, Nested
, which extends from this class. When you try to invoke the super constructor
public Nested(String str, Boolean b , Number nm) { super("2",true); }
it will fail because the super constructor, for Inner
, depends on an instance of Outer
, which doesn't exist in the static
context of the Nested
class. Jon Skeet provides a solution.
An explanation of the solution appears in the JLS here.
Superclass constructor invocations may be subdivided:
Unqualified superclass constructor invocations begin with the keyword super (possibly prefaced with explicit type arguments).
Qualified superclass constructor invocations begin with a Primary expression.
- They allow a subclass constructor to explicitly specify the newly created object's immediately enclosing instance with respect to the direct superclass (§8.1.3). This may be necessary when the superclass is an inner class.
Solution 2
As Sotirios has said, your nested (not-inner) class doesn't implicitly have an instance of Outer
to effectively provide to the Inner
.
You can get round this, however, by explicitly specifying it before the .super
part:
public Nested(String str, Boolean b, Number nm) {
new Outer(10).super("2", true);
}
Or even accept it as a parameter:
public Nested(Outer outer) {
outer.super("2", true);
}
However, I would strongly advise you to avoid such convoluted code. I avoid nested classes most of the time, named inner classes almost always, and I can't ever remember using a combination of them like this.
gstackoverflow
Updated on March 02, 2020Comments
-
gstackoverflow about 4 years
I investigate java inner classes.
I wrote example:
public class Outer { public Outer(int a){} public class Inner { public Inner(String str, Boolean b){} } public static class Nested extends Inner{ public static void m(){ System.out.println("hello"); } public Nested(String str, Boolean b , Number nm) { super("2",true); } } public class InnerTest extends Nested{ public InnerTest(){ super("str",true,12); } } }
I invoke it from main using following string:
new Outer(1).new Inner("",true);
I see compile error:
java: no enclosing instance of type testInheritancefromInner.Outer is in scope
Can you explain me this situation?
UPDATE
-
Alexei Kaigorodov over 6 yearsthe reference to an instance of outer class to use in a constructor like
outer.super()
can be not only a parameter, but also a field. This way you can quietly extend an inner class being outside its outer class.