JAVA PROGRAMMING Chapter 11 Flashcards
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Questions and Answers

Is the statement Apple p = new McIntosh() legal?

True

Is fruit instanceof Orange true?

False

Is fruit instanceof Macintosh true?

False

Can fruit invoke the method makeApple?

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

Can orange invoke the method makeOrangeJuice?

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

Is the statement Orange p = new Apple() legal?

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

What causes a runtime ClassCastingException?

<p>Object apple = (Apple)fruit;</p> Signup and view all the answers

Does every object have a toString method and an equals method?

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

Is mistyping the equals method signature a common mistake?

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

What will the output be for circle1.equals(circle2) using method (a)?

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

What will the output be for circle1.equals(circle2) using method (b)?

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

What happens when you call list.remove('Dallas') one time?

<p>The list becomes {'Dallas', 'Houston', 'Dallas'}</p> Signup and view all the answers

Can you add a Date object to a list of Strings?

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

Is it correct to run System.out.println(java.util.Collections.max(array)) on a primitive array?

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

What access does the protected keyword provide?

<p>Access to the same class, subclasses, and classes in the same package.</p> Signup and view all the answers

Can final classes be extended?

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

Can a class with default modifier be accessed by a class in a different package?

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

What should the modifier be so that a class in the same package can access it, but a class in a different package cannot?

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

How do you prevent a method from being overridden?

<p>Set the method to final.</p> Signup and view all the answers

Is a protected datum accessible by any class in different packages?

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

What does inheritance allow in programming?

<p>Defining a general class and extending it to specialized classes</p> Signup and view all the answers

What is a superclass?

<p>The class a subclass inherits from.</p> Signup and view all the answers

What is a child class?

<p>The class that inherits from a superclass.</p> Signup and view all the answers

What keyword indicates that a class is extending another superclass?

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

True or false? Java allows multiple inheritance directly from multiple classes.

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

What is single inheritance?

<p>A JAVA class may inherit directly from only one superclass.</p> Signup and view all the answers

True or false? A subclass is a subset of a superclass.

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

What keyword is used to define a subclass?

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

What is the output of running class C in a given example?

<p>A's no-arg constructor is invoked</p> Signup and view all the answers

How does a subclass invoke its superclass's constructor?

<p>Using the super keyword.</p> Signup and view all the answers

True or false? When invoking a constructor from a subclass, its superclass's no-arg constructor is always invoked.

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

What is overriding a method?

<p>Recreating a method in the subclass with the same signature.</p> Signup and view all the answers

True or false? You can override a private method defined in a superclass.

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

True or false? You can override a static method defined in a superclass.

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

What is the benefit of using the @Override annotation?

<p>It forces the compiler to check the overridden method's signature.</p> Signup and view all the answers

What is the ultimate parent or superclass in Java?

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

What is polymorphism?

<p>Allows a variable of a supertype to refer to a subtype object.</p> Signup and view all the answers

What are the three pillars of object-oriented programming?

<p>Encapsulation, Inheritance, Polymorphism</p> Signup and view all the answers

What is dynamic binding?

<p>A method can be implemented in several classes along the inheritance chain.</p> Signup and view all the answers

True or false? Casting an object reference generates a new object.

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

True or false? You can always successfully cast an instance of a superclass to a subclass.

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

Study Notes

Inheritance

  • Inheritance allows creating a superclass (general class) and extending it to subclasses (specialized classes) that inherit properties and methods.
  • Subclasses usually contain more methods than the superclass.
  • Private data fields in a superclass are inaccessible to subclasses, accessed only through getters and setters.
  • The "is-a" relationship must be relevant; not all relationships are suitable for inheritance.
  • Java supports single inheritance directly but can implement multiple inheritance through interfaces.

Class Types

  • Superclass/Parent/Base Class: The class from which a subclass derives.
  • Child Class/Extended Class/Derived Class: The class that inherits properties and methods from the superclass.

Inheritance Concepts

  • The extends keyword is used to define a subclass.
  • Single inheritance permits a subclass to inherit from only one superclass.
  • Java does not allow multiple inheritance but permits a superclass with an interface.

Constructors and Method Overriding

  • The super keyword invokes a superclass's methods and constructors.
  • Superclass constructors are invoked using super() as the first statement in the subclass constructor.
  • Constructor chaining occurs when a subclass constructor calls its superclass constructor before executing its own tasks.
  • Overriding a method must match the original signature and return type and is annotated with @Override.

Static and Private Methods

  • Private and static methods cannot be overridden.
  • Access modifiers and return types must align for successful method overriding.

Polymorphism and Dynamic Binding

  • Polymorphism enables superclass variable types to refer to subclass objects.
  • Dynamic binding allows the JVM to choose the method implementation at runtime based on the object type.
  • Declared type of a variable determines method matching at compile time while actual type determines method binding at runtime.

Casting

  • Implicit casting allows subclass variables to be used as superclass references.
  • Explicit casting is required when downcasting objects, which can result in a ClassCastException if improperly handled.
  • The instanceof keyword checks if an object of a certain type can reference a specific subclass.

Object Class Methods

  • Every object in Java has a toString() and equals() method defined in the Object class, typically overridden for customized behavior.### Equals Method in Java
  • Incorrectly overriding the equals method can lead to errors; it should take Object as a parameter instead of the specific class (e.g., equals(Object o)).
  • Using an incorrectly overridden equals method results in always returning false when comparing instances, as signatures do not match during the compile-time check.
  • Correct overriding allows proper comparison leading to a true output when checking instances with the correct type.
  • Use of instanceof in the equals method is crucial for type safety and avoiding runtime errors when comparing different object types.

ArrayList Operations

  • Create an ArrayList for double values with ArrayList<Double> list = new ArrayList<>();.
  • Append an object with list.add(object);.
  • Insert at the beginning with list.add(0, object);.
  • Get the count of objects using list.size();.
  • Remove a specific object with list.remove(object);.
  • Remove the last object with list.remove(list.size() - 1);.
  • Check if an object exists using list.contains(object);.
  • Retrieve an object at a specific index using list.get(index);.

Code Error Identification

  • Adding incompatible types (e.g., Date to a String ArrayList) leads to compilation errors.
  • Attempting to access an index that does not exist results in IndexOutOfBoundsException.

List Modifications

  • Removing an item from a list only removes the first instance; subsequent calls require a loop or a different approach.
  • Use a while loop with i-- after a successful removal to correctly iterate and check against the new list size.

Integer and Object Management in Lists

  • Java's type system requires care when handling primitive types; using Double rather than int directly avoids issues in lists.
  • For collections, convert primitive arrays to wrapper class arrays for methods like Arrays.asList().

Access Modifiers in Java

  • Protected: Members are accessible in the same package and by subclasses. More open than private but controlled compared to public.
  • Private: Members are rigidly private, only accessible within the same class.
  • Public: Members are fully accessible by any class, enabling broader functionality.
  • Default (package-private): Members are accessible only within the same package.

Final Keyword

  • Declaring a class or method as final prevents inheritance or overriding, ensuring that the intended behavior remains unchanged.
  • Final classes can still be instantiated, but they cannot be derived from.

Access Modifier Statements Evaluation

  • True: A protected method or variable can be accessed in the same package.
  • False: A protected method cannot be accessed by all classes in different packages, only by subclasses.
  • True: Subclasses in any package have access to protected members.
  • True: Final classes can have instances created.
  • False: Final classes cannot be extended.
  • False: Final methods cannot be overridden.

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Explore key concepts of Inheritance and Polymorphism in Java programming through interactive flashcards. This quiz will help reinforce your understanding of how subclasses inherit properties and methods from superclasses, as well as the accessibility of private data fields. Perfect for students looking to solidify their grasp of object-oriented programming.

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