Questions and Answers
A compiler error will result if an anonymous inner class tries to use a variable that is not final, or not effectively final.
True
A functional interface is simply an interface that has one abstract method.
True
An abstract class is not instantiated, but serves as a superclass for other classes.
True
All methods in an abstract class must also be declared abstract.
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Every class has a toString method and an equals method inherited from the Object class.
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Every class is either directly or indirectly derived from the Object class.
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If a method in a subclass has the same signature as a method in the superclass, the subclass method overloads the superclass method.
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If two methods in the same class have the same name but different signatures, the second overrides the first.
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Inheritance involves a subclass, which is the general class, and a superclass, which is the specialized class.
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In an inheritance relationship, the subclass constructor always executes before the superclass constructor.
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It is not possible for a superclass to call a subclass's method.
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Private members of the superclass cannot be accessed by the subclass.
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When a subclass extends a superclass, the public members of the superclass become public members of the subclass.
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When an interface variable references an object, you can use the interface variable to call any and all of the methods in the class implementing the interface.
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A subclass can directly access:
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A subclass may call an overridden superclass method by:
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All fields declared in an interface:
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An anonymous inner class must:
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Given the following code, which of the following is TRUE? public class ClassB implements ClassA{}
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If a class contains an abstract method:
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If a superclass does not have a default constructor or a no-arg constructor:
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Study Notes
Compiler Errors and Variables
- Anonymous inner classes can use variables only if they are final or effectively final. Using non-final variables will lead to compiler errors.
Functional Interfaces
- A functional interface is defined as an interface with exactly one abstract method.
Abstract Classes
- Abstract classes cannot be instantiated and serve as a foundation for derived classes.
- Not all methods in an abstract class need to be declared as abstract; some can have a concrete implementation.
Object Class Methods
- Every Java class inherits a
toStringmethod and anequalsmethod from theObjectclass. - All classes in Java are ultimately derived from the
Objectclass.
Method Overloading and Overriding
- If a method in a subclass shares the same signature with a superclass method, it overrides, not overloads, the superclass method.
- Overloading occurs when methods within the same class share names but have different signatures, while overriding represents method redefinition in subclasses.
Inheritance Relationships
- Inheritance features a superclass (general class) and a subclass (specialized class), opposite to the incorrect assertion that a subclass serves as a general class.
- The superclass constructor executes before the subclass constructor in an inheritance hierarchy.
Access Modifiers in Inheritance
- Superclass methods cannot call subclass methods directly.
- Private members in a superclass are inaccessible to subclasses.
- Public members of a superclass become public members in the subclass.
Interface Variables and Methods
- When an interface variable references an object, not all methods from the implementing class can be called; only those defined by the interface can be accessed.
- Interface variables are inherently final and static, meaning they cannot be changed once initialized.
Inner Classes
- Anonymous inner classes must either extend another class or implement an interface.
Class Implementation and Inheritance
- If a class implements an interface (e.g.,
public class ClassB implements ClassA{}), it is required to override every abstract method defined in that interface. - Classes containing abstract methods must define those methods with only a header, omitting the implementation details.
Constructor Behavior
- A subclass inheriting from a superclass without a default constructor must explicitly call one of the available constructors in the superclass to ensure proper instantiation.
Summary of Public Access
- A subclass has access to only the public and protected members of its superclass but cannot access private members.
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Description
Test your knowledge of Java concepts with this quiz covering chapters 10 through 16, including compiler errors and functional interfaces. Designed for students to review key definitions and true/false statements related to Java's advanced features. Perfect for a final exam preparation or a quick revision session.
