COP3502 Programming Fundamentals for CIS Majors 1

Instructor: Parisa Rashidi

Chapter 7:Multi-Dimensional

Arrays

Declaring and creating 2-dimensional array

2D Array

// Combine declaration and creation in one // single statementdouble[][] myTable = new double[10][10];

// Alternative syntaxdouble myTable[][] = new double[10][10];

//you might skip specifying the 2nd dimensiondouble myTable[][] = new double[10][];

2-dimensional array illustration Accessing elements

2D Array

0 0 0 0 0

0 0 0 0 0

0 7 0 0 0

0 0 0 0 0

0 0 0 0 0

0 1 2 3 4

0

1

2

3

4

matrix[2][1] =7;

What is nums.length? 5

What is nums[0].length? 4

2D Array

int [][] nums = new int[5][4];

nums

2-dimensional array illustration Initialization

2D Array

1 2 3

10 3 0

10 7 80

0 1 2

0

1

2

int[][] matrix2 = { {1, 2, 3}, {10, 3, 0}, {10, 7, 80}};

matrix2

1 2 3

10 3 0

10 7 80

Rows might have different lengths

Ragged Array

int[][] matrix = { {1, 2, 3, 4, 5}, {2, 3, 4, 5}, {3, 4, 5}, {4, 5}, {5}};

matrix

1 2 3 4 5

2 3 4 5

3 4 5

4 5

5

Loops and 2D arrays

Loops & 2D Array

for (int row = 0; row < matrix.length; row++) { for (int column = 0; column < matrix[row].length; column+

+) { // use matrix[row][column] }}

1 2 3

10 3 0

10 7 80

In Java, you can create n-dimensional arrays for any integer n. Generalization of 2D case Example

Multi-dimensional array

 double[][][] scores = new double[10][5][2];

What is the output of the following code?

Q

Q/A

0 0 0 0 0 0array

0 0 0 0 0 0

0 0 0 0 0 0

0 0 0 0 0 0

0 0 0 0 0 0

int[][] array = new int[5][6];int x = {1, 2};

x 1 2

Q/A

array

0 0 0 0 0 0

0 0 0 0 0 0

0 0 0 0 0 0

0 0 0 0 0 0

array[0] = x;

x 1 2

0 0 0 0 0 0

array[0][1]?

Chapter 8: Objects & Classes

object An entity in the real world that can be

distinctly identified. A student, a desk, a circle, a button, and

even a loan can all be viewed as objects. has a unique identity, state, and

behaviors. State = a set of data fields (also known as

properties) with their current values. Behavior = a set of methods

Object

Class Example

class Circle { /** The radius of this circle */ double radius = 1.0; /** Construct a circle object */ Circle() { } /** Construct a circle object */ Circle(double newRadius) { radius = newRadius; } /** Return the area of this circle */ double getArea() { return radius * radius * 3.14159; }

}

Data field

Method

Constructors

UML class diagram

UML Notation

Circle

radius: double Circle()

Circle(newRadius: double)

getArea(): double

circle1: Circle radius = 1.0

Class name

Data fields

Constructors and methods

circle2: Circle radius = 25

circle3: Circle radius = 125

UML Class Diagram

UML notation for objects

Constructors are a special kind of methods that are invoked to construct objects.

Constructor

Circle(double newRadius) { radius = newRadius;}

Constructor with no

argument

Constructor with

argument

Circle() {}

Constructors must have the same name as the class itself.

Constructors do not have a return type—not even void.

Constructors are invoked using the new operator when an object is created.

Constructors play the role of initializing objects.

Constructor

A class may be declared without constructors.

In this case, a no-arg constructor with an empty body is implicitly declared in the class. This constructor, called a default

constructor, is provided automatically only if no constructors are explicitly declared in the class.

Constructor

Declaring & creating objects in a single step

Two steps

Creating Objects

Circle myCircle = new Circle();

declare create

//step 1: declareCircle myCircle;//step 2: createmyCircle = new Circle();

Referencing the object’s data fields:

Invoking the object’s method:

Access

myCircle.radius

myCircle.getArea()

The default value of a data field is null for a reference type 0 for a numeric type false for a boolean type '\u0000' for a char type

However, Java assigns no default value to a local variable inside a method.

Default Values

Static methods are not tied to a specific object.

Static variables are shared by all the instances of the class.

Static constants are final variables shared by all the instances of the class.

All declared using static keyword

Static

Static fields or methods can be used from instance or static methods.

Instance fields or methods can be only used from instance methods.

So: a variable or method that does not depend on a specific instance of the class, should be specified as static.

Static vs. Instance

1. Package access (default in Java)

The class, variable, or method can be accessed by any class in the same package.

2. public

The class, data, or method is visible to any class in any package.

3. private

The data or methods can be accessed only by the declaring class.

Accessibility

The get and set methods are used to read and modify private properties. Data encapsulation

get/set

Circle

-radius: double

-numberOfObjects: int

+Circle()

+Circle(radius: double)

+getRadius(): double

+setRadius(radius: double): void

+getNumberOfObject(): int

+getArea(): double

The radius of this circle (default: 1.0).

The number of circle objects created.

Constructs a default circle object.

Constructs a circle object with the specified radius.

Returns the radius of this circle.

Sets a new radius for this circle.

Returns the number of circle objects created.

Returns the area of this circle.

What is wrong?

Q

What is wrong?

Q

What is wrong?

Q

What is wrong?

Q

What is wrong?

Q

Suppose that the class Foo is defined in (a). Let f be an instance of Foo. Which of the statements in (b) are correct?

Q

Question on the next slide …

Q

What is the output?

Q

Chapter 10:Thinking in Objects

For a class to be immutable, it must 1. Mark all data fields private 2. Provide no mutator methods 3. Provide no accessor methods that

would return a reference to a mutable data field object.

Immutable

For a class to be immutable, it must 1. Mark all data fields private 2. Provide no mutator methods 3. Provide no accessor methods that

would return a reference to a mutable data field object.

Immutable

The scope of instance and static data fields is the entire class. They can be declared anywhere inside

a class.

The scope of a local variable starts from its declaration and continues to the end of the block that contains the variable. A local variable must be initialized

explicitly before it can be used.

Variable Scope

Example

Variable Scope

If a local variable has the same name as a class’s variable, the local variable takes precedence and the class’s variable with the same name is hidden.

Variable Scope

Example

Variable Scope

Using this to reference hidden fields

this

Use this to call overloaded constructor

this

Composition is a special case of the “aggregation” relationship.

Aggregation models “has-a” relationships.

The owner object is called an aggregating object.

The subject object is called an aggregated object.

Aggregation

UML composition & aggregation notation

UML

Is the following class immutable?

Q

What is the output?

Q