SCJP Inner Classes and Nested Types

Question 1

Which statement about a static nested class is TRUE?

Accepted Answer

It can be instantiated without an instance of the outer class

Answer

A static nested class is associated with the outer class itself, not with an instance. You instantiate it as `new Outer.Nested()` without needing an Outer instance. It cannot access instance members of the outer class directly.

Question 2

What is the correct syntax to create an instance of the non-static inner class `Inner` defined inside class `Outer`?

Accepted Answer

Outer o = new Outer(); Outer.Inner i = o.new Inner();

Answer

A non-static inner class is tied to an instance of its enclosing class. You must first create an Outer instance, then use the `outerRef.new Inner()` syntax. The other forms are not valid Java.

Question 3

A method-local inner class defined inside an instance method can access which variables from the enclosing method?

Accepted Answer

Only local variables declared final (or effectively final in Java 8+)

Answer

A method-local inner class can access the enclosing class's instance/static members freely, but can only access local variables that are final (Java 6 SCJP rule). This is because the class instance may outlive the method's stack frame.

Question 4

Which of the following is a valid way to create an anonymous class in Java?

Accepted Answer

Runnable r = new Runnable() { public void run() {} };

Answer

Anonymous classes are created with `new InterfaceOrClass() { /* body */ }`. There is no `anonymous` keyword, no `class` keyword in the syntax, and no parentheses-only form without `new`.

Question 5

Can a non-static inner class declare static members?

Accepted Answer

Yes, but only static final constant fields

Answer

In Java, a non-static inner class may declare static final constant fields (compile-time constants) but cannot declare other static members. This is because the inner class is associated with an outer instance and full static context would be ambiguous.

SCJP - Sun Certified Java Programmer Practice Test

SCJP - Sun Certified Java Programmer Practice Test

SCJP Inner Classes and Nested Types