Class Bag

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Class Bag
public class Bag private final int GROWBY
3 private int num 0 private Object
list //Class Object! public Bag ( int size
) if ( size lt GROWBY ) list
new ObjectGROWBY else list
new Objectsize public void add (
Object obj ) . . . private void grow()
. . . ...
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Method getCount()
public int getCount() return num
Should num be public? NO! Access Methods
getCount() Modification Methods add() and
remove() No setCount()!
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Usage of the Bag Class
Bag myBag Object obj // Whats the
count? System.out.println(Count
myBag.getCount()) // No object! myBag new
Bag(-1) // Whats the count? System.out.println(
Count myBag.getCount()) myBag.add( obj
) // Whats the count? System.out.println(Count
myBag.getCount()) // No object!
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Usage of the Bag Class
Bag myBag Object obj myBag new Bag(10) //
Whats the count? System.out.println(Count
myBag.getCount()) Obj new Object() myBag.add(
obj ) // Whats the count? System.out.println(C
ount myBag.getCount()) myBag.add( new
Date() ) System.out.println(Count
myBag.getCount()) // Can we do this? // Whats
the count?
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Usage of the Bag Class
Bag myBag new Bag() Object obj new
Object() // Will it work? myBag.add( obj ) No
default constructor!
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Class Bag
public class Bag private final int GROWBY
3 private int num 0 private Object
list / public Bag ( int size )
if ( size lt GROWBY ) list new
ObjectGROWBY else list new
Objectsize / ... Comment out the
constructor.
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Usage of the Bag Class
Bag myBag new Bag() Object obj new
Object() // Whats the count? System.out.println
(Count " myBag.getCount()) // Will it
work? myBag.add( obj ) NullPointerException! Arr
ay list is not initialized! The default
constructor sets it to null.
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Class Bag
public class Bag private final int GROWBY
3 private int num 0 private Object
list // Assuming list points to an array
object (not null) public void add ( Object obj
) if ( num list.length )
grow() listnum obj
...
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Initializing Array
public class Bag private final int GROWBY
3 private int num 0 private Object
list ... public void add ( Object obj )
if ( list null ) list new
ObjectGROWBY if ( num list.length )
grow() listnum obj
...
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Initializing Array
public class Bag private final int GROWBY
3 private int num 0 private Object
list new ObjectGROWBY ... public void
add ( Object obj ) if ( num
list.length ) grow()
listnum obj ...
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Initializing Array
public class Bag private final int GROWBY
3 private int num private Object
list public Bag() list new
ObjectGROWBY num 0 ...
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Method Find
// Private method to be used by implementer //
inside the class private int find ( Object obj
) for (int i 0 i lt num i ) if (
listi.equals( obj ) ) return i
return -1
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Method Remove
// Removes one object from list that equals
obj public boolean remove ( Object obj ) int
index find( obj ) if ( index gt 0 )
listindex list--num return
true return false
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Method RemoveAll
// Removes all objects from list that equal
obj public void removeAll( Object obj ) int
index find( obj ) while ( index gt 0 )
listindex list--num index
find( obj ) Zero or more objects will be
removed. Is it efficient?
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Efficient Implementation of RemoveAll
// Removes all objects from list that equal
obj public int removeAll( Object obj ) int
index 0, count 0 while ( index lt num )
if ( listindex.equals(obj) )
listindex list--num count
else index
return count
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Testing
Test-bed main The entire class As
implementer Can access private data/methods Check
results
Junit Individual methods As User Can NOT access
private data/methods assertEquals assertTrue asse
rtFalse
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• public void testAverage()
• System.out.println("average")
• ScoresList instance new ScoresList()
• float expResult 0.0F
• float result instance.average()
• assertEquals(expResult, result, 0.0)
• // TODO review the generated test code and
• // remove the default call to fail.
• fail("The test case is a prototype.")

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• public void testAverage()
• System.out.println("average")
• ScoresList instance new ScoresList()
• float expResult 0.0F
• float result instance.average()
• assertEquals(expResult, result, 0.0)
• instance.appendScore( 55.5F )
• expResult 55.5F
• result instance.average()
• assertEquals(expResult, result, 0.001)
• // result between 55.499 and 55.501 are good

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Schedule

• Quiz2 Next Monday
• Test 1 Next Friday
• Class on Friday