UML Basics & Access Modifier

Transcript UML Basics & Access Modifier

UML Basics & Access Modifier
UML Basics
Java: UML Diagrams
EVE does Java
UML Diagram – Class & Object
A class is described using a rectangle box with three sections.
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The top section gives the class name, the middle section describes the
fields, and the bottom section describes the methods. The middle and
bottom sections are optional, but the top section is required.
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An object is described using a rectangle box with two sections.
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The top section is required. It gives the object’s name and its defining class.
The second section is optional; it indicates the object’s field values.
The Access Modifiers
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The symbols +, - and # are used to denote, respectively,
public, private, and protected modifiers in the UML. The
static fields and methods are underlined.
The Access Modifiers -- public
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public access modifier: the + sign in UML
Fields, methods and constructors declared public (least
restrictive) within a public class are accessible by all
class in the Java program, whether these classes are in
the same package or in another package.
For simplicity, just take package as the file folder in
Windows
Note: in one application program, there is only and only
one public class
Fields/methods are called Class fields/method/member,
i.e., you don’t need to create an instance to use them;
the convention is to use the classname.methodName
notation
The Access Modifiers -- private
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private access modifier: the – sign in UML
The private (most restrictive) fields or
methods cannot be accessed outside the
enclosing/declaring class. To make all fields
private, provide public getter/setter methods
for them.
The getter is used to set the values of the
data fields
The setter is used to change/modifier the
fields
The Access Modifiers -- protected
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protected access modifier: the # sign in UML
Fields, methods and constructors declared
protected in a class can be accessed only by
subclasses in other packages and by those in
the same class even if they are not a subclass
of the protected member’s class.
The Access Modifiers -- default
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default access modifier: without any sign
when no access modifier is present, any
class, field, method or constructor are
accessible only by classes in the same
package.
This is also called the instance members, i.e.,
must create an instance of the class before
the fields/methods can be used
Use the instanceName.method() format
What is the Modifier?
+constructor()
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Public
Private
Final
Protected
Static
Default
Good!
What is this Modifier?
-radius: double
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Public
Private
Final
Protected
Static
Default
Good!
What is this one?
+ numberOfObjects(): int
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Public
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Private
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Final
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Protected
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Static
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Default
Good!
What is this one?
# aMethod(): void
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Public
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Private
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Final
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Protected
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Static
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Default
Answer the following:
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How do you tell which method is a constructor?
To access private methods, you need
public _______ and ________ methods.
(Also called Accessors and Mutators)
A modifier with no symbol is accessible
only within the same folder or __________.
see
see
see
Now let’s build a program
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The name of the
class will be, of
course, Rectangle.
class Rectangle
Rectangle class
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class Rectangle
{
// Data members
private double width = 1, height = 1;
private static String color = "yellow";
It has two
private or local
variables, and
a static or
global variable
that is shared.
Rectangle class
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// Constructor
public Rectangle()
{
}
The default
constructor (with no
parameters) - it will
use the initialized
values for height,
width, and color.
Rectangle class
// Constructor
public Rectangle(double width, double height)
{
this.width = width
this.height = height;
 The Rectangle constructor
}
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needs two doubles.
If you wish to use the same
name in the parameters
(formal and actual) you use
this.
Rectangle class
public double getWidth()
{
return width;
}
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In order to access or make
changes to private variables,
you need sets and gets.
(Accessors and Mutators)
Rectangle class
public double getWidth()
{
return width;
}
public double getHeight()
{
return height;
}
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This is to access a Rectangle
object’s height and width
after it is constructed.
Rectangle class
public static String getColor()
{
return color;
}
public static void setColor(String color)
{
Rectangle.color = color;
}
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Color is static- it can be shared – and
changed- with all rectangle objects.
Rectangle class
public double getArea()
{
return width * height;
}
public double getPerimeter()
{
return 2 * (width + height);
}
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Now we just need the methods to get
the area and perimeter of a rectangle
object.
Rectangle class
class Rectangle {
// Data members
private double width = 1, height = 1;
private static String color = "yellow";
// Constructor
public Rectangle() {
}
// Constructor
public Rectangle(double width, double height) {
this.width = width;
this.height = height;
}
Now put it all together
and compile it.
public double getWidth() {
return width;
}
public double getHeight() {
return height;
}
public static String getColor() {
return color;
}
public static void setColor(String color) {
Rectangle.color = color;
}
Did you get it?
public double getArea() {
return width * height;
}
public double getPerimeter() {
return 2 * (width + height);
}
}
TestRectangle class
To see if it works you now have to
create a TestRectangle class.
- which includes main.
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public class TestRectangle
{
public static void main(String[] args)
{
TestRectangle class
Rectangle myRect1 = new Rectangle();
Rectangle myRect2 = new Rectangle(4, 40);
Rectangle myRect3 = new Rectangle(3.5, 35.9)
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Let’s create three rectangles, one
default and two with different
parameters.
TestRectangle class
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To see if it worked, let’s print out the first
one. Compile and run. Get it?
System.out.println("The area of the rectangle is "
+ myRect1.getArea());
System.out.println("The perimeter is "
+ myRect1.getPerimeter());
System.out.println("The color is "
+ myRect1.getColor());
TestRectangle class
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This is the rectangle object with no
parameters. You can print out the height and
width if you wish.
The area of a rectangle with width 1.0 and height
1.0 is 1.0
The perimeter of a rectangle is 4.0
The color is yellow
TestRectangle class
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Now try the next rectangle using (4,40).
System.out.println("The area of the rectangle is "
+ myRect2.getArea());
System.out.println("The perimeter is "
+ myRect2.getPerimeter());
System.out.println("The color is "
+ myRect2.getColor());
TestRectangle class
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Did you get it?
The area of the rectangle is 160.0
ÏÏ§ÏThe perimeter is 88.0
ÏÏ§ÏThe color is yellow
TestRectangle class
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Let’s try something a little different.
Set the color for the third rectangle to “red”
before you print it out.
myRect3.setColor("red");
System.out.println("The area of the
rectangle is "
+ myRect3.getArea());
System.out.println("The perimeter is "
+ myRect3.getPerimeter());
System.out.println("The color is "
+ myRect3.getColor());
TestRectangle class
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Did you get it?.
ÏThe area of the rectangle is
125.64999999999999
ÏÏ§ÏThe perimeter is 78.8
ÏÏ§ÏThe color is red
ÏÏ§Ï

UML Basics & Access Modifier

Transcript UML Basics & Access Modifier

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