Questions and Answers
Which are true about a static nested class? (Choose all that apply)
Which create an anonymous inner class from within class Bar? (Choose all that apply)
Which are true about a method-local inner class? (Choose all that apply)
What is the result of the given code? (Choose one)
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What is the result of the given code? (Choose one)
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What is the result of the given code? (Choose one)
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Which, inserted independently at line 6, compile and produce the output 'spooky'? (Choose all that apply)
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What is the result of the given code? (Choose one)
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Which, inserted independently at line 5, produce the output 'hi'? (Choose all that apply)
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What is the result of the given code? (Choose one)
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What is the result of the given code? (Choose one)
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What is the result of the given code? (Choose one)
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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.