Slide 1

Pointers Prasun Dewan Comp 114 Slide 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 Slide 3 vector.elementAt(3) 5new Integer(5) Wrapper Classes AStringDatabase AStringHistoryString Object intbooleanchardouble wrapper class Joe Doe.toString() 5.toString() Vector vector = new Vector() vector.addElement(Joe Doe) vector.addElement(5) vector.addElement(new Integer(5)) (new Integer(5)).toString() vector.elementAt(3).intValue() Number Integer Double wrapper class Slide 4 Other Wrapper Classes Double 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 Slide 5 Storing Primitive Values/Variables 5 5.5 48 double d 52 int i 80 double e 85.5 5 16 5 int i = 5; memory address double d = 5.5; same size same, double size double e = d; Slide 6 Storing Objects Values/Variables 16 8 5.5 Double@8 860 Integer I 5 16 Integer@16 48 Double D Integer I = new Integer(5) Double D = new Double(5.5) memory address different sizes variables same size Slide 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;} } Slide 8 Structured Objects 16 80 5.5 Double@8 860 Integer I 5 16 Integer@16 96 Point p 50 100 80 APoint@80 48 Double D public class APoint implements Point { // instance vars int x, y; //methods } Point p = new APoint(50, 100) Slide 9 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 Slide 10 Inheritance public class APoint implements Point { int x, y; } new ABoundedPoint(75, 75, new APoint(50,50), new APoint(100,100) ) 8 16 50 APoint@8 8 48 ABounded Point@48 100 16 APoint@16 100 75 public class ABoundedPoint extends APoint { Point upperLeftCorner ; Point lowerRightCorner; } Slide 11 Assignment of Object Variables Point p1 = new APoint(50, 50); Point p2 = p1; 50 APoint@8 8 8 16 Point p1 8 48 Point p2 P1P2 APoint@8 p1.setX(100); Slide 12 Assignment of Object Variables Point p1 = new APoint(50, 50); Point p2 = p1; 100 50 APoint@8 8 16 8 Point p1 8 48 Point p2 p1.setX(100); p2.getX() 100 P1P2 APoint@8 p1 = new APoint(200,200); Slide 13 Assignment of Object Variables 100 50 200 APoint@8 64 200 16 48 8 Point p1 APoint@64 8Point p2 64 Point p2 = p1; p1 = new APoint(200,200); p2.getX() 100 p1.setX(100); p2.getX() 100 Point p1 = new APoint(50, 50); P1P2 APoint@64APoint@8 p2 = p1; Slide 14 Assignment of Object Variables 100 50 200 APoint@8 64 200 16 48 8 Point p1 APoint@64 64Point p2 64 Point p2 = p1; p1 = new APoint(200,200); p2.getX() 100 p2 = p1; p2.getX() 200 p1.setX(100); p2.getX() 100 Point p1 = new APoint(50, 50); P1P2 APoint@64APoint@8 Garbage collected Slide 15 == for Objects 200 APoint@8 64 200 16 48 8 Point p1 APoint@64 8Point p2 64 Point p2 = new APoint(200, 200) Point p1 = new APoint(200, 200); P1P2 APoint@64APoint@8 p2 == p2 false Same physical object? Slide 16 == for Objects 200 APoint@8 8 16 48 8 Point p1 8Point p2 Point p2 = p1; Point p1 = new APoint(200, 200); p2 == p2 true P1P2 APoint@8 Slide 17 == vs. Equal for Strings Joe Doe String@8 64 16 48 8 String s1 String@64 8String s2 64 String s2 = Joe Doe String s1 = Joe Doe; S1S2 String@64String@8 s1 == s2 false s1.equals(s2) true Slide 18 == vs. equals() for Objects 200 APoint@8 64 200 16 48 8 Point p1 APoint@64 8Point p2 64 Point p2 = new APoint(200, 200) Point p1 = new APoint(200, 200); p2 == p2 false public boolean equals(Point otherPoint) { return x == otherPoint.getX() && y == otherPoint.getY(); } p1.equals(p2) true Slide 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 Slide 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 Slide 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 Slide 22 Bounded Point Copy? public ABoundedPoint copy() { return new ABoundedPoint (x, y, upperLeftCorner, lowerRightCorner); }; Slide 23 Shallow Copy Slide 24 Deep Copy Slide 25 Bounded Point Deep Copy public ABoundedPoint copy() { return new ABoundedPoint (x, y, upperLeftCorner.copy(), lowerRightCorner.copy()); }; Slide 26 Shallow vs. Deep Copy Shallow copy: Copies the instance but not its components Deep copy Copies the instance and deep copies the components