Question

Write a class JPS 33 that represents a \(3 \times 3\) integer matrix. Include a constructor that creates the specified JPS33. Include a to String method that returns the three-line representation.

Short answer

Define a class with a constructor for the 3x3 matrix and a `toString` method for string representation.

Step-by-step solution

Define the Class Structure

Start by defining the basic class structure for `JPS33`. This includes the class declaration and the initialization of member variables that will store the matrix data. The matrix will be represented using a two-dimensional integer array of size 3x3.

Implement the Constructor

Create a constructor for `JPS33` that takes a two-dimensional integer array as a parameter. This array represents the 3x3 matrix. Within the constructor, assign this parameter to the class's array member variable after validating that the input is indeed a 3x3 matrix.

Implement the toString Method

Develop the `toString` method in the `JPS33` class. This method should traverse the matrix and create a string representation where each row of the matrix is represented as a separate line. Concatenate the integers with spaces in between to form the lines, ensuring proper alignment and readability.

Review and Testing

After implementing the class and its methods, test by creating instances of `JPS33` using different 3x3 matrices. Call the `toString` method on these instances to ensure the output is as expected and matches the three-line format.

Key concepts

Class Structure

In Java programming, a class serves as a blueprint for creating objects. It defines the properties and behaviors that the objects created from the class can have. When you design a class like `JPS33`, which represents a 3x3 integer matrix, you need to start with defining your class structure.

• The class declaration should begin with the keyword `class` followed by the class name, in this case, `JPS33`.
• Inside the class, you will define member variables. These are the variables that hold the object's data.

For a matrix, the data can be stored using a two-dimensional array, specifically an integer array in this scenario. Each element of this array represents an integer value in the matrix, organized into rows and columns. The size of your array should be defined to ensure that it can store a 3x3 matrix. This not only helps in organizing the data but also in keeping the structure clear and manageable.

Constructor Method

A constructor method in Java is a special type of method that is used to initialize objects. When you create an instance of a class, the constructor is automatically called. For the `JPS33` class, the constructor's purpose is to set up the initial state of the matrix.

• Constructors have the same name as the class and do not have a return type.
• In the `JPS33` class, the constructor should accept a parameter that is a two-dimensional integer array.

This parameter represents the initial data for the 3x3 matrix. Ensuring that this parameter correctly represents a 3x3 configuration before assigning it to the class's internal variable is crucial. A check can be performed within the constructor to verify that the length of both dimensions of the array is 3. If everything is valid, assign the array to your class's matrix variable. This assignment finalizes the setup of your matrix at the creation of an object.

Two-Dimensional Array

A two-dimensional array in Java is like a grid, containing rows and columns. It is useful for representing data that is naturally structured in this form, such as matrices. For the `JPS33` class that handles a matrix, a two-dimensional array allows for intuitive data management.

• The syntax for declaring a two-dimensional array in Java involves two pairs of brackets, like `int[][] matrix`.
• Accessing elements requires specifying both the row and the column index, e.g., `matrix[0][1]` accesses the element in the first row and second column.

The arrangement of data in this way means you can easily traverse the matrix, perform operations, or output its contents. When representing a 3x3 matrix, ensure each sub-array (row) contains exactly three elements, providing uniformity and predictability across the structure.

Matrix Representation

Matrix representation is crucial when you want to visually display or internally manage a matrix's contents in a program. In the `JPS33` class, creating a `toString` method allows you to convert the matrix data into a human-readable string format. This can greatly aid in debugging and presenting data.

• The `toString` method should loop through each row of the matrix, convert the integers to strings, and concatenate them with spaces in between.
• This output can then be formatted to have each row of the matrix on a separate line for clarity.

Java handles string concatenation using the `+` operator, but for larger scale or more complex requirements, considering the `StringBuilder` can provide performance benefits. This form of matrix representation not only makes it easy to view the data but also helps in ensuring that your matrix logic correctly maps each element to its intended place in a formatted output.