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Inheritance: is a

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  1. Inheritance: is a A Checking Account is a Bank Account A Interest Checking Account is a Checking Account public class CheckingAccount extends BankAccount { // class body goes here } public class InterestCheckingAccount extends CheckingAccount { // class body goes here } ITK 179

  2. Object This is done implicitly Shape {abstract} extends Java’s World in UML Rectangle Circle ThreeD {interface} RectanglePrism Cylinder implements ITK 179

  3. Shape (I) package gray.adts.shapes; publicabstractclass Shape { protectedstaticfinaldoubleDEFAULT_SIZE = ( double ) 1.0; protectedstaticfinal String DEFAULT_NAME = "Unknown"; private String shapeName; public Shape() { this.shapeName = DEFAULT_NAME; } public Shape( String name ) { setShapeName( name ); } protectedvoid setShapeName( String name ) { if ( name.trim().length() == 0 ) shapeName = DEFAULT_NAME; elseshapeName = new String( name ); } public String getShapeName() { returnshapeName; } ..... ..... } ITK 179

  4. Shape (II) package gray.adts.shapes; publicabstractclass Shape { ......... ......... /* * Get the surface area of this Shape * and return the surface area of this Shape */ publicabstractdouble getSurfaceArea(); /** * Get the perimeter of this <tt>Shape</tt>. * and return the perimeter of this <tt>Shape</tt> */ publicabstractdouble getPerimeter(); } ITK 179

  5. There are some details that are not as important to the concepts (classes) ITK 179

  6. Circle (I) package gray.adts.shapes; publicclass Circle extends Shape { privatedoubleradius; public Circle() { super( "Circle" ); setRadius( super.DEFAULT_SIZE ); } public Circle( double theRadius ) { super( "Circle" ); if ( theRadius <= 0.0 ) { setRadius( Shape.DEFAULT_SIZE ); } else { setRadius( theRadius ); } } ...... ...... } ITK 179

  7. Circle (II) package gray.adts.shapes; publicclass Circle extends Shape { privatedoubleradius; ..... ..... publicdouble getRadius() { returnthis.radius; } publicvoid setRadius( double theRadius ) { if ( theRadius <= 0 ) { return; } this.radius = theRadius; } publicdouble getSurfaceArea() { returnthis.radius * this.radius * Math.PI; } publicdouble getPerimeter() { return 2 * this.radius + Math.PI; } } ITK 179

  8. equality and “what is” double s,t; .... .... if (s == t) .... .... .... System.out.println(“This value of s is “ + s); .... .... ITK 179

  9. the default method use identities to do the job. Object’s toString andequals methods Shape {abstract} Now, we have a better idea about how this job to be done. Rectangle Circle ITK 179

  10. Rectangle package gray.adts.shapes; publicclass Rectangle extends Shape { .... .... public String toString() { returnthis.getShapeName() + ": length = " + this.length + ", height = " + this.height; } publicboolean equals( Object o ) { if ( ( o == null ) || ( ! ( o instanceof Rectangle ) ) ) { returnfalse; } return ( ( ( ( Rectangle ) o ).getLength() == getLength() ) && ( ( ( Rectangle ) o ).getHeight() == getHeight() ) ); } ..... } So, this method can take any object of any class. ITK 179

  11. Shape {abstract} Extend to three-dimension How to unify the interface? Rectangle Circle RectanglePrism Cylinder ITK 179

  12. Object Shape {abstract} interface Rectangle Circle RectanglePrism Cylinder implements ITK 179

  13. ThreeD package gray.adts.shapes; publicinterface ThreeD { double getDepth(); void setDepth( double theDepth ); double getVolume(); } must be all abstract Any class implements the interface must implement all methods in the interface. Some interfaces don’t even have the body called marker interface. ITK 179

  14. Cylinder (I) package gray.adts.shapes; publicfinalclass Cylinder extends Circle implements ThreeD { privatedoubledepth; public Cylinder() { this( Shape.DEFAULT_SIZE, Shape.DEFAULT_SIZE ); } public Cylinder( double theRadius, double theWidth ) { setShapeName( "Cylinder" ); if ( theRadius <= 0.0 ) { setRadius( Shape.DEFAULT_SIZE ); } else { setRadius( theRadius ); } if ( theWidth <= 0.0 ) { setDepth( Shape.DEFAULT_SIZE ); } else { setDepth( theWidth ); } } .... } ITK 179

  15. Cylinder (II) package gray.adts.shapes; publicfinalclass Cylinder extends Circle implements ThreeD { privatedoubledepth; .... publicdouble getSurfaceArea() { return 2 * super.getSurfaceArea() + 2 * Math.PI * getRadius() * getDepth(); } publicdouble getPerimeter() { return 2 * super.getPerimeter() + 4 * this.depth; } publicdouble getVolume() { returnthis.depth * super.getSurfaceArea(); } publicdouble getDepth() {returnthis.depth;} publicvoid setDepth( double theDepth ) { if ( theDepth <= 0 ) return; this.depth = theDepth; .... } ITK 179

  16. Cylinder (III) package gray.adts.shapes; publicfinalclass Cylinder extends Circle implements ThreeD { privatedoubledepth; .... public String toString() { returnsuper.toString() + ", depth = " + getDepth(); } publicboolean equals( Object o ) { if ( super.equals( o ) && ( ( Cylinder ) o ).getDepth() == this.getDepth() ) { returntrue; } else { returnfalse; } } } ITK 179

  17. UML: Extends and Implements Extending 2D shapes to 3D shapes extends UML inheritance diagram – The dotted line indicates a class implements an interface. For example, Cylinder extends Circle and implements ThreeD. implements See next slide ITK 179

  18. Example of using shapes import gray.adts.shapes.*; import javax.swing.JOptionPane; publicclass TestShape { publicstaticvoid main ( String [] args ) { String output; Cylinder c1 = new Cylinder( 3.5, 7.2 ); Cylinder c2; Shape s = c1; RectangularPrism rp1 = new RectangularPrism(); Cylinder cyl1 = new Cylinder(); c2 = (Cylinder) s; output = "c1 = " + c1.toString() + "\n"; output += "c2 = " + c2.toString() + "\n"; output = “c2 volume = " + c2.getVolume() + "\n"; JOptionPane.showMessageDialog( null, output, "shape-cylinder cast exercise", JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); } } ITK 179

  19. Generic Types in Java Format for a generic (parameterized) type and instantiation of a generic type Type variable publicclass Pair < T > { ... ... T ... ... ... T ... } Type declaration Pair < Integer > aPair1, aPair2; Type instantiation Actual Type ITK 179

  20. A generic type declaration (I) publicclass Pair<T> { private T firstElement; private T secondElement; public Pair() { this.firstElement = null; this.secondElement = null; } public Pair(T e1, T e2) { if ( (e1 == null) || (e2 == null)) { thrownew NullPointerException(); } this.firstElement = e1; this.secondElement = e2; } public T getFirstElement() { returnthis.firstElement; } ..... } ITK 179

  21. A generic type declaration (II) publicclass Pair<T> { private T firstElement; private T secondElement; .... .... publicvoid swapElements() { T temp = this.firstElement; this.firstElement = this.secondElement; this.secondElement = temp; } public T equals(T e) { if (e == null) { thrownew NullPointerException(); } if(this.firstElement.equals(e) || this.secondElement.equals(e)){ return e; } elsereturnnull; } ..... } ITK 179

  22. A generic type instantiation Pair < Integer > intPair; Pair < String > strPair = new Pair<String>(“ISU”, “ITK 179”); intPair = new Pair<Integer>( new Integer(1), new Integer(2)); ITK 179