1. Pointers
Prasun Dewan
Comp 114

2. Pointers Primitive values vs. objects Wrapper Classes
Memory Representation of Primitive Values Vs Objects
Pointers
Equal Vs ==
Sharing of Objects
Garbage Collection
Shallow vs. Deep copy

3. (new Integer(5)).toString()
Wrapper Classes
“Joe Doe”.toString()
Object
Vector vector = new Vector()
Number
Integer
vector.addElement(“Joe Doe”)
(new Integer(5)).toString()
new Integer(5) 5
String
AStringHistory
vector.addElement(new Integer(5))
Double
vector.elementAt(3).intValue()
vector.elementAt(3)
AStringDatabase
wrapper class
wrapper class
5.toString()
char
boolean
double
int
vector.addElement(5)

4. Other Wrapper Classes Double Boolean Character Float, Short, Long
public Double(double value)
public double doubleValue()
Boolean
public Boolean(boolean value)
public boolean booleanValue()
Character
public Character(char value)
public char charValue()
Float, Short, Long

5. Storing Primitive Values/Variables8
5.5
int i = 5;
same, double size
memory address 5 16
same size 48
double d
5.5
double d = 5.5; 52
int i 5
double e = d; 80
double e
5.5

6. Storing Objects Values/Variables
5.5 8
Integer I = new Integer(5)
different sizes
Double D = new Double(5.5) 5 16 48
Double D 8
variables same size
memory address 60
Integer I 16

7. Structured Objects public class APoint implements Point { int x, y;
public APoint (int initX, int initY) {
x = initX; y = initY; }
public int getX() {return x};
public void setX(int newVal) {x = newVal;}
public int getY() {return y};
public void setY(int newVal) {y = newVal;}

8. Structured Objects 5.5 Double@8 8 5 16 Integer@16 48 Double D 60
public class APoint implements Point {
// instance vars
int x, y;
//methods … }
5.5 8 5 16 48
Double D 60
Integer I 16
Point p = new APoint(50, 100) 50
100 80 96
Point p 80

9. Superclass Constructor
Inheritance
public class ABoundedPoint extends APoint {
APoint upperLeftCorner, lowerRightCorner;
public ABoundedPoint (int initX, int initY, Point initUpperLeftCorner, Point initLowerRightCorner) {
super(initX, initY);
upperLeftCorner = initUpperLeftCorner;
lowerRightCorner = initLowerRightCorner; } …
Superclass Constructor

10. Inheritance 50 APoint@8 8 100 16 APoint@16 48 ABoundedPoint@48 75 8 16
public class APoint implements Point {
int x, y; … } 50 8
100 16
public class ABoundedPoint extends APoint {
Point upperLeftCorner ;
Point lowerRightCorner; … } 48 75 8 16
new ABoundedPoint(75, 75, new APoint(50,50), new APoint(100,100) )

11. Assignment of Object Variables
Point p1 = new APoint(50, 50); 8 50
Point p2 = p1; 50
p1.setX(100); 16
Point p1 8 P1 P2 48
Point p2 8

12. Assignment of Object Variables
Point p1 = new APoint(50, 50); 8
100
Point p2 = p1; 50
p1.setX(100);
p2.getX()
100 16 8
Point p1
p1 = new APoint(200,200); P1 P2 48
Point p2 8

13. Assignment of Object Variables
Point p1 = new APoint(50, 50); 8
100
Point p2 = p1; 50
p1.setX(100);
p2.getX()
100 16 64
Point p1
p1 = new APoint(200,200);
p2.getX()
100
p2 = p1; 48 8
Point p2 P1 P2 64
200
200

14. Assignment of Object Variables
Point p1 = new APoint(50, 50); 8
100
Point p2 = p1; 50
p1.setX(100);
p2.getX()
100 16 64
Point p1
p1 = new APoint(200,200);
p2.getX()
100
p2 = p1;
p2.getX()
200 48 64
Point p2 P1 P2 64
200
200
Garbage collected

15. == for Objects Point p1 = new APoint(200, 200); 8 200 APoint@8
p2 == p2
 false
Same physical object? 16 64
Point p1 48 8
Point p2 P1 P2 64
200
200

16. == for Objects Point p1 = new APoint(200, 200); 8 200 APoint@8
Point p2 = p1;
200
p2 == p2
 true 16 8
Point p1 P1 P2 48 8
Point p2

17. == vs. Equal for Strings String s1 = “Joe Doe”; 8 Joe Doe String@8
 false 16 64
String s1
s1.equals(s2)
 true 48 8
String s2 S1 S2 64
Joe Doe

18. == vs. equals() for Objects
Point p1 = new APoint(200, 200); 8
200
Point p2 = new APoint(200, 200)
200
p2 == p2
 false 16 64
Point p1
p1.equals(p2)
 true 48 8
Point p2 64
200
public boolean equals(Point otherPoint) {
return x == otherPoint.getX() &&
y == otherPoint.getY(); }
200

19. Copying Objects p1 = new APoint(200, 200); p2 = p1; p1.setX (100);
What if we want copy rather than reference.
The properties can be changed independently
Backup

20. Copier does the work p1 = new APoint(200, 200);
p2 = new APoint (p1.getX(), p1.getY());
p1.setX (100);
What if we want copy rather than reference.
The properties can be changed independently
Backup

21. Copied object does the work
p1 = new APoint(200, 200);
p2 = p1.copy();
p1.setX (100);
Class APoint defines:
public Point copy() {
return new APoint(x, y); }
All copiers reuse the copy code

22. Bounded Point Copy? public ABoundedPoint copy() {
return new ABoundedPoint (x, y, upperLeftCorner, lowerRightCorner); };

23. Shallow Copy

24. Deep Copy

25. Bounded Point Deep Copy
public ABoundedPoint copy() {
return new ABoundedPoint (x, y, upperLeftCorner.copy(), lowerRightCorner.copy()); };

26. Shallow vs. Deep Copy Shallow copy: Deep copy
Copies the instance but not its components
Deep copy
Copies the instance and deep copies the components