Java Inner Classes Quiz
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Questions and Answers

Which are true about a static nested class? (Choose all that apply)

  • It does not have access to non-static members of the enclosing class (correct)
  • You must have a reference to an instance of the enclosing class in order to instantiate it
  • It must extend the enclosing class
  • Its variables and methods must be static
  • If the outer class is named MyOuter, and the nested class is named MyInner, it can be instantiated using new MyOuter.MyInner(); (correct)
  • Which create an anonymous inner class from within class Bar? (Choose all that apply)

  • Boo f = new Boo(24) { };
  • Bar f = new Boo(String s) { };
  • Boo f = new Bar() { }; (correct)
  • Boo f = new Boo() {String s; }; (correct)
  • Boo f = new Boo.Bar(String s) { };
  • Which are true about a method-local inner class? (Choose all that apply)

  • It can be marked static
  • It can access private members of the enclosing class (correct)
  • It can be marked abstract (correct)
  • It can be marked public
  • It must be marked final
  • What is the result of the given code? (Choose one)

    <p>Compilation fails because of an error on a line other than 3, 4, or 8</p> Signup and view all the answers

    What is the result of the given code? (Choose one)

    <p>Compilation fails because of an error on line 10</p> Signup and view all the answers

    What is the result of the given code? (Choose one)

    <p>57 22</p> Signup and view all the answers

    Which, inserted independently at line 6, compile and produce the output 'spooky'? (Choose all that apply)

    <p>Cathedral.Sanctum s = c.new Sanctum();</p> Signup and view all the answers

    What is the result of the given code? (Choose one)

    <p>middle</p> Signup and view all the answers

    Which, inserted independently at line 5, produce the output 'hi'? (Choose all that apply)

    <p>{ Car.this.drive(); }</p> Signup and view all the answers

    What is the result of the given code? (Choose one)

    <p>No output is produced</p> Signup and view all the answers

    What is the result of the given code? (Choose one)

    <p>21</p> Signup and view all the answers

    What is the result of the given code? (Choose one)

    <p>Compilation fails</p> Signup and view all the answers

    Study Notes

    Static Nested Classes

    • Static nested classes do not require a reference to an instance of the enclosing class to be instantiated.
    • They cannot access non-static members of the enclosing class, similar to static methods.
    • The instantiation syntax for a static nested class includes enclosing class name, e.g., new MyOuter.MyInner();.
    • Static nested classes are not inherently required to extend the enclosing class.

    Anonymous Inner Classes

    • Anonymous inner classes can express polymorphism, allowing a superclass reference to refer to a subclass instance.
    • Correct instantiation involves using valid constructors as per defined class constructors.
    • Syntax should follow Java standards to avoid compilation errors.

    Method-local Inner Classes

    • Method-local inner classes can be declared abstract, but require subclasses to be instantiated.
    • They have access to all members of the enclosing class, including private members.
    • Local inner classes within methods cannot be marked public or static.

    Compilation and Runtime Errors

    • Proper syntax is crucial; missing semicolons or incorrect method signatures can lead to compilation errors.
    • Object references made through superclass types can only access defined members of the superclass.

    Class Scope and Access Modifiers

    • Inner class declarations impact method scope; a local inner class cannot overshadow an outer class declaration.
    • Accessing outer class methods must be utilized with correct syntax, depending on context (e.g., from an initialization block).

    Exception Handling

    • Proper exception handling is important in method overrides; checking for exceptions ensures safe execution of methods.
    • Inner classes can redefine methods from their enclosing classes and must correctly rethrow exceptions when required.

    Access to Private Members

    • Inner classes have special access privileges to the private members of the enclosing class.
    • This includes both instance and static variables of the enclosing class.

    Comparator Usage

    • To use an inner class implementing an interface like Comparator in static contexts, the inner class must be declared static.
    • The use of sorting functions will depend on correctly implementing the compare method within the inner class.

    Key Results

    • Compilation errors can arise from improper references, incorrect inner class declarations, or logical issues.
    • Understanding the scope, visibility, and syntax of classes, especially nested and inner classes, is essential for Java programming.

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    Description

    Test your knowledge on Java Inner Classes, including static nested classes, anonymous inner classes, and method-local inner classes. This quiz will cover their characteristics, instantiation syntax, and access to class members.

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