Which of the following Is Legal Declaration of a Method in an Abstract Class

12 Δεκεμβρίου, 2022 Χωρίς κατηγορία

Sometimes we just need a method declaration in superclasses. This can be achieved by specifying the abstract type modifier. These methods are sometimes referred to as subclass responsibility because no implementation is specified in the parent class. Therefore, a subclass must replace it to provide a method definition. To declare an abstract method, use the following general form: Which of the following class definitions defines a legal abstract class? If a class contains abstract methods, the class itself must be declared abstract, as follows: What is the most restrictive access modifier that allows members of one class to access members of another class in the same package? For a nested class, it can also be declared private or protected. Which of the following statements about abstract classes is true? In this case, class X must be abstract because it does not fully implement Y, but class XX actually implements Y. The declaration referred to in point (c) is not legal because the variables cannot be declared abstract. Which one should you use, abstract classes or interfaces? A class declaration can only have definitive, abstract, and public modifiers, unless it is a nested class. Abstract and native modifiers apply to methods, but not to fields. An abstract class is a class declared abstract, which may or may not contain abstract methods. Abstract classes cannot be instantiated, but they can be subordinate. Note: Although abstract classes cannot be used to instantiate objects, they can be used to create object references because the Java approach to runtime polymorphism is implemented through the use of superclass references.

Therefore, it must be possible to create a reference to an abstract class so that it can be used to refer to a subclass object. Which of the following methods declares an abstract method in a Java abstract class? An example of an abstract class in the JDK is AbstractMap, which is part of the Collections Framework. Subclasses (which include HashMap, TreeMap, and ConcurrentHashMap) use many methods (including get, put, isEmpty, containsKey, and containsValue) defined by AbstractMap. Static and final keywords are valid modifiers for field and method declarations. As you can see, there is no method text. Any concrete class (that is.class without an abstract keyword) that extends an abstract class must replace all abstract methods of the class. Important rules for abstract methods: Abstract and native apply only to member methods. An abstract method is a method declared without implementation (without curly braces and followed by a semicolon), as follows: There is no abstract key in statement 3.The statement is true, but it is not an abstract class or interface.

1. Final abstract class Test {}2. public static interface Test {}3. last public class Test {}4. Protected abstract class Test {}5. protected interface Test {}6. abstract public class Test {} In an object-oriented drawing application, you can draw circles, rectangles, lines, Bézier curves, and many other graphic objects. These objects all have specific states (for example, position, alignment, line color, fill color) and behavior (for example, move, rotate, resize, draw) together. Some of these states and behaviors are the same for all graphic objects (for example, position, fill color, and moveTo).

Others require different implementations (such as resizing or drawing). All GraphicObjects must be able to draw or resize. They differ only in the way they do it. This is a perfect situation for an abstract superclass. You can take advantage of similarities and declare that all graphic objects inherit from the same abstract parent object (for example, GraphicObject), as shown below. In a method, a local variable can be declared as final. An example class in the JDK that implements multiple interfaces is HashMap, which implements the Serializable, Cloneable, and Map interfaces. If you read this list of interfaces, you can conclude that a HashMap instance can be cloned (regardless of the developer or company that implemented the class), is serializable (meaning it can be converted to byte streams; see the section Serializable objects), and has the functionality of a map. In addition, many standard methods, such as merge and forEach, have been added to the Map interface, which older classes that implemented this interface do not need to define. Options A and C are wrong because public and protected are less restrictive.

Options B and D are incorrect because abstract and synchronized are not access modifiers. (3), (6). Both are legal collective declarations. (1) is erroneous because a class cannot be abstract and definitive “there would be no way to use such a class”. (2) is incorrect because interfaces and classes cannot be marked as static. (4) and (5) are incorrect because classes and interfaces cannot be marked as protected. Any non-abstract subclass of GraphicObject, such as Circle and Rectangle, must provide implementations for the draw and resize methods: First, you declare an abstract class, GraphicObject, to provide member variables and methods that are fully shared by all subclasses, such as the current position and the moveTo method. GraphicObject also declares abstract methods for methods such as draw or resize, which must be implemented by all subclasses, but must be implemented in different ways.

The GraphicObject class might resemble the following: An abstract class can have static fields and static methods. You can use a class reference (for example, use AbstractClass.staticMethod()) as with any other class. Note that many software libraries use both abstract classes and interfaces. The HashMap class implements several interfaces and also extends the abstract AbstractMap class. When an abstract class is subclassed, the subclass typically provides implementations for all abstract methods of its parent class. However, if this is not the case, the subclass must also be declared abstract. Transient and volatile modifiers are valid only for item field declarations. Which of them is not a legal declaration of membership within a class? In the Interfaces section, it was noted that a class that implements an interface must implement all methods of the interface. However, it is possible to define a class that does not implement all the methods of the interface, provided that the class is declared abstract. For example, abstract classes look like interfaces. You cannot instantiate them, and they can contain a combination of methods declared with or without implementation. However, abstract classes allow you to declare fields that are not static and definitive, and to define public, protected, and private concrete methods.

With interfaces, all fields are automatically public, static, and definitive, and all methods you declare or define (as default methods) are public. In addition, you can only extend one class, whether abstract or not, while you can implement any number of interfaces. Consider the following Java program, which demonstrates the use of abstract keywords with classes and methods. Given the following code: public class School{ public abstract double numberOfStudent(); } which of the following statements is true?. To resolve the issue and compile option B, you must add an additional pair of braces: Rectangle, Line, Bezier, and Circle classes Inherit from GraphicObject The default access is the “packet-oriented” access modifier. » Your comments will only be displayed after manual approval.

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