CS100J%20Lecture%2025

1
CS100J Lecture 25

• Previous Lecture
• Inheritance
• Method overriding
• Polymorphism
• This Lecture
• Application of inheritance
• Higher-order" methods
• Abstract classes
• Visibility modifier protected

2
Recall class ML Method add

• // x y
• public static ML add(ML x, ML y)
• if ( x.isEmpty() y.isEmpty() )
• return new ML(0,0)
• else if ( x.isScalar() )
• ML result new ML(y.h, y.w)
• ml scalarValue x.values00
• for (int r 0 r lt y.h r)
• for (int c 0 c lt y.w c)
• result.valuesrc
• ml.add( scalarValue,
• y.valuesrc )
• return result
• else if ( y.isScalar() )
• ML result new ML(x.h, x.w)

3
Recall class ML Method add, continued

• else if (x.h ! y.h x.w ! y.w)
• throw new RuntimeException(
• matrix dimensions do not match")
• else
• ML result new ML(x.h, x.w)
• for (int r 0 r lt x.h r)
• for (int c 0 c lt x.w c)
• result.valuesrc
• ml.add( x.valuesrc,
• y.valuesrc)
• return result
• // end of method add

4
Recall Class ml Arithmetic Methods

• public static ml add(ml x, ml y)
• return new ml(x.re y.re, x.im y.im)
• public static ml sub(ml x, ml y)
• return new ml(x.re - y.re, x.im - y.im)
• / other operators
• . ./ lt lt gt gt unary- etc.
• /

5
Recall the Critique of ML Method add

• Most of the code (all but the 3 invocations of
  ml.add) has nothing to do with the fact that this
  is the method for addition.
• To implement subtraction, almost all code (except
  for the 3 invocations of ml.add) would be
  identical.
• We could implement each of the other
  element-by-element matrix operations in about 30
  seconds each
• Copy the definition of ML.add
• Replace add with sub, or mult, or div,
  etc.
• Write ml.add, ml.mult, ml.div, etc.
• Terrible
• Grotesque duplication of code.
• Loss of single point of change.
• No abstraction.
• Surely, there must be a way to avoid duplicating
  the common code.
• Coming later...
• Now is that time

6
class ML Method Binary

• // x op y
• public static ML Binary(
• OP o, // where method o.op combines 2 mls.
• ML x, // left operand.
• ML y // right operand.
• )
• if (x.isEmpty() y.isEmpty())
• return new ML(0,0)
• else if (x.isScalar())
• ML result new ML(y.h, y.w)
• ml scalarValue x.values00
• for (int r 0 r lt y.h r)
• for (int c 0 c lt y.w c)
• result.valuesrc
• o.op( scalarValue,
• y.valuesrc)
• return result

7
class ML Method Binary, continued

• else if ( y.isScalar() )
• ML result new ML(x.h, x.w)
• ml scalarValue y.values00
• for (int r 0 r lt x.h r)
• for (int c 0 c lt x.w c)
• result.valuesrc
• o.op( x.valuesrc,
• scalarValue)
• return result
• else if (x.h ! y.h x.w ! y.w)
• throw new RuntimeException(
• matrix dimensions do not match")
• else
• ML result new ML(x.h, x.w)
• for (int r 0 r lt x.h r)
• for (int c 0 c lt x.w c)

8
Class OP a class of binary operations

• class OP
• // A placeholder binary operation.
• ml op(ml x, ml y)
• return null
• class BinaryAdd extends OP
• ml op(ml x, ml y)
• return ml.add(x,y)
• class BinarySub extends OP
• ml op(ml x, ml y)

9
Class ML Methods add and sub

• // x y
• public static ML add(ML x, ML y)
• return ML.Binary(new BinaryAdd(), x, y)
• // x - y
• public static ML sub(ML x, ML y)
• return ML.Binary(new BinarySub(), x, y)

10
Sample Client Code

• // ones(2,3) ones(2,3)
• ML.add( ML.ones(2,3), ML.ones(2,3) )
• Evaluation of expression
• ML.add(,)
• invokes
• ML.Binary(new BinaryAdd(), , )
• which invokes
• BinaryAdd.op(,)
• to add pairs of complex matrix elements, which
  invokes
• ml.add(,)

11
Abstract Classes

• abstract class OP
• // A placeholder binary operation.
• abstract ml op(ml x, ml y)
• class BinaryAdd extends OP
• ml op(ml x, ml y)
• return ml.add(x,y)
• class BinarySub extends OP
• ml op(ml x, ml y)
• return ml.sub(x,y)

12
An Application of Inheritance

• abstract class OP
• static int count 0 // ml operations.
• // A placeholder binary operation.
• abstract ml op(ml x, ml y)
• class BinaryAdd extends OP
• ml op(ml x, ml y)
• count
• return ml.add(x,y)
• class BinarySub extends OP
• ml op(ml x, ml y)

13
Visibility Modifier Protected

• Recall the visibility modifiers of constructors,
  methods, or fields
• public A public item is visible anywhere in the
  program
• private A private items is only visible in the
  class in which the item is declared or defined.
  In particular, a private item declared or defined
  in class c is not visible in the subclasses of a
  class c
• The new visibility modifier
• protected A protected item is visible in the
  class in which the item is declared or defined,
  and in any subclasses of that class

14
Visibility Modifier Protected

• abstract class OP
• // ml operations.
• protected static int count 0
• // A placeholder binary operation.
• abstract ml op(ml x, ml y)
• static int getCount() return count
• class BinaryAdd extends OP
• ml op(ml x, ml y)
• count
• return ml.add(x,y)

15
Sample Client Code

• // ones(2,3) ones(2,3)
• System.out.println(
• ML.add( ML.ones(2,3), ML.ones(2,3) )
• )
• / Output the total number of primitive ml
  operations performed by all matrix operations to
  date. /
• System.out.println(
• OP.getCount()
• )
• Output
• 2 2 2
• 2 2 2
• 6