Question

Fill in the blanks in cach of the following: a) Each class declaration that begins with keyword ______ must be stored in a file that has exactly the same name as the class and ends with the .java filename extension. b) Keyword ______ in a class declaration is followed immediately by the class's name. c) Keyword ______ requests memory from the system to store an object, then calls the corresponding class's constructor to initialize the object. d) Each parameter must specify both a(n) ______ and \(a(n)\) ______ e) By default, classes that are compiled in the same directory are considered to be in the same package, known as the ______ f) Java provides two primitive types for storing floating-point numbers in memory: ______ and ______ g) Variables of type double represent ______ floating-point numbers. h) Scanner method ______ returns a double value. i) Keyword public is an access ______ j) Return type ______ indicates that a method will not return a value. k) Scanner method ______ reads characters until it encounters a newline character, then returns those characters as a String. I) Class String is in package______ \(\mathrm{m}) \mathrm{A}(\mathrm{n})\) is not required if you always refer to a class with its fully qualified class name. n) \(A(n)\) ______ is a number with a decimal point, such as 7.33,0.0975 or 1000.12345 o) Variables of type float represent ______ -precision floating-point numbers. p) The format specifier ______ is used to output values of type \(f\) loat or double. q) Types in Java are divided into two categories ______ types and ______

Short answer

a) public b) class c) new d) type, identifier e) default package f) float, double g) double-precision h) nextDouble i) modifier j) void k) nextLine l) java.lang m) import statement n) floating-point number o) single p) %f q) primitive, reference

Step-by-step solution

Fill in the blank for (a)

The answer is 'public'. Each class declaration that begins with keyword 'public' must be stored in a file that has exactly the same name as the class and ends with the .java filename extension.

Fill in the blank for (b)

The answer is 'class'. Keyword 'class' in a class declaration is followed immediately by the class's name.

Fill in the blank for (c)

The answer is 'new'. Keyword 'new' requests memory from the system to store an object, then calls the corresponding class's constructor to initialize the object.

Fill in the blank for (d)

The answer is 'type' and 'identifier'. Each parameter must specify both a(n) 'type' and a(n) 'identifier'.

Fill in the blank for (e)

The answer is 'default package'. By default, classes that are compiled in the same directory are considered to be in the same package, known as the 'default package'.

Fill in the blank for (f)

The answers are 'float' and 'double'. Java provides two primitive types for storing floating-point numbers in memory: 'float' and 'double'.

Fill in the blank for (g)

The answer is 'double-precision'. Variables of type double represent 'double-precision' floating-point numbers.

Fill in the blank for (h)

The answer is 'nextDouble'. Scanner method 'nextDouble' returns a double value.

Fill in the blank for (i)

The answer is 'modifier'. Keyword public is an access 'modifier'.

Fill in the blank for (j)

The answer is 'void'. Return type 'void' indicates that a method will not return a value.

Fill in the blank for (k)

The answer is 'nextLine'. Scanner method 'nextLine' reads characters until it encounters a newline character, then returns those characters as a String.

Fill in the blank for (l)

The answer is 'java.lang'. Class String is in package 'java.lang'.

Fill in the blank for (m)

The answer is 'import statement'. An 'import statement' is not required if you always refer to a class with its fully qualified class name.

Fill in the blank for (n)

The answer is 'floating-point number'. A(n) 'floating-point number' is a number with a decimal point, such as 7.33, 0.0975 or 1000.12345.

Fill in the blank for (o)

The answer is 'single'. Variables of type float represent 'single'-precision floating-point numbers.

Fill in the blank for (p)

The answer is '%f'. The format specifier '%f' is used to output values of type float or double.

Fill in the blank for (q)

The answers are 'primitive' and 'reference'. Types in Java are divided into two categories: 'primitive' types and 'reference' types.

Key concepts

Class Declaration

In Java programming, the cornerstone of any application is the class. It is the blueprint from which individual objects are created. A class declaration starts with access modifiers such as 'public', which signal the visibility of the class to other classes within the program.

For example, if a class is public and named 'Book', you must save this class in a file named 'Book.java'. Within this class, you define variables and methods that will belong to the objects of this class. Following the keyword 'class', you provide the class name which sets the identifier by which the class will be referenced. Declaring a class correctly is crucial because it affects the accessibility and organization of your code, which can lead to better maintainability and fewer errors in large applications.

It is also worth noting that when classes are compiled in the same directory without a specified package, they belong to what is known as the 'default package'. This offers convenience during small-scale development but is typically avoided for larger, more complex applications due to potential naming conflicts and the benefits of package namespaces in code organization.

Object Initialization

Object initialization in Java is a two-step process involving the 'new' keyword and a constructor. When you use the 'new' operator, Java allocates memory for the new object. Then, it invokes the constructor method of the corresponding class to initialize the newly allocated object.

This process is critical as it sets up the state of the object with default or specified values. For instance, if you have a class named 'Student', initialization would look like this: 'Student student1 = new Student();'. Here, 'student1' becomes a reference to the new object, and any constructor logic defined in the 'Student' class is executed to initialize 'student1'. Leaving a newly created object uninitialized can lead to errors and undefined behavior in your program because the object's properties might not have appropriate values.

Understanding object initialization is pivotal because it allows you to control the creation of your objects accurately and prevent resource leaks or other issues related to improperly initialized instances in a Java application.

Primitive and Reference Types

Java has two categories of types: primitive types and reference types. Primitive types include basic data types such as 'int', 'float', 'double', and 'boolean'. These types represent single values and are not objects. For example, 'float' represents a single-precision floating-point number while 'double' represents a double-precision floating point number, allowing for more digits to be used and therefore more precision.

On the other hand, reference types refer to objects and store the memory address where the object is located, instead of the data itself. For instance, when you create a 'String' object, you are working with a reference type that points to the space in memory where the actual characters of the string are stored. It's important to understand this distinction as it affects how data is managed and manipulated in memory. Primitive types tend to be more efficient because they require less memory and the values are accessed directly, while reference types offer more flexibility and are used to work with complex data structures, such as objects and arrays, and to define relationships between different parts of a program.

The use of primitive types and reference types is deeply ingrained in Java’s design philosophy, offering a balance between performance optimization and object-oriented programming, which allows developers to pick the most appropriate type for the data or object they need to represent.