Post on 08-Jan-2016
description
1CompSci 105 SS 2005
Principles of Computer Science
Lecture 10: References and Objects
Lecturer: Santokh Singh
2
Abstract Data Types
Program that uses the ADT
ADTImplementation
AD
T O
perations
Textbook, p. 110
3
Java Interfacepublic interface Circle {
void setX ( float x );
void setY ( float y );
void setRadius( float r );
float getX ();
float getY ();
float getRadius();
float getArea ();
}
4
public class MyCircle implements Circle
{
float x, y, radius;
void setRadius( float newRadius ) {
radius = newRadius;
}
float getArea() {
return ( Math.PI * radius * radius );
}
}
5public class AreaCircle implements Circle
{
float x, y, radius, area;
void setRadius( float newRadius ) {
radius = newRadius;
area = Math.PI * radius * radius ;
}
float getArea() {
return ( area );
}
}
6
Interface Circle
Class MyCircle(fast setRadius)(slow getArea)
Class MyCircle(slow setRadius)
(fast getArea)
7
A method that uses Circle
public boolean isBigger( Circle A,
Circle B)
{
if ( A.getArea() > B.getArea() )
return(true);
else
return(false);
}
8
A method that uses MyCircle
public boolean isBigger( MyCircle A,
MyCircle B)
{
if ( A.getArea() > B.getArea() )
return(true);
else
return(false);
}
9
Creating Circles
Circle A = new MyCircle();
Circle B = new AreaCircle();
MyCircle C = new MyCircle();
AreaCircle D = new AreaCircle();
boolean x = isBigger( A, B );
boolean y = isBigger( C, D );
10
ADTs: Multiple Implementations
Program that uses the ADT
ADTImplementation
1
AD
T O
perations ADTImplementation
2
11
Changing the radius
AreaCircle A = new AreaCircle();
A.setRadius(.5);
12
The Wall
Program that uses the ADT
ADTImplementation
AD
T O
perations
Textbook, p. 110
13public Class AreaCircle implements Circle
{
private float x, y, radius, area;
public void setRadius( float newR ) {
radius = newRadius;
area = Math.PI * radius * radius );
}
public void getArea() {
return ( area );
}
}
14
In Tutoral 5 ….
• Array implementation of List ADT
15
The Towers of HanoiTextbook pp. 85-91
Source Target Spare
16
References and Objects
Object Storage
Object References
Diagramming Objects and References
Garbage Collection
Example: Equality
Example: Parameter Passing
Example: Resizable Arrays
17
Arrays: Index and Value
731 98anArray:
first:
last:
0 1 2 3 4
18
Java Reference Variables
Integer intRef = new Integer(5);
intRef:
Textbook, pp. 153-154
19
Digramming References
intRef: 5
p:
Integer intRef = new Integer(5);
Integer p = null;
20
Diagramming References
Integer p, q;
p = new Integer(5);
p = new Integer(6);
q = p;
q = new Integer(9);
p = null;
q = p;
p: q:
Textbook, pp. 155
21
Garbage Collection
Integer p, q;
p = new Integer(5);
p = new Integer(6);
q = p;
q = new Integer(9);
P = null;
q = p;
p: q:
Textbook, pp. 155
22
References and Objects
Object Storage
Object References
Diagramming Objects and References
Garbage Collection
Example: Equality
Example: Parameter Passing
Example: Resizable Arrays
23
Equality of References
Integer p, q;
p = new Integer(5);
q = new Integer(5);
if ( p == q )
println(“Equal”);
else
println(“Not”);
p: q:
24
Equality of References
Integer p, q;
p = new Integer(5);
p = new Integer(5);
if ( p.equals(q) )
println(“Equal”);
else
println(“Not”);
p: q: