Growable Bag Continued

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Growable Bag Continued
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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 // Default constructor
public Bag () list new
ObjectGROWBY ...
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Methods
public void add ( Object obj ) if ( num
list.length ) grow() listnum
obj private void grow() Object temp
new Objectlist.length GROWBY for (int i
0 i lt num i ) tempi listi
list temp public int getCount() return
num
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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 Write it the dirty way
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Method Remove
// Removes one object from list that equals
obj public void remove ( Object obj ) int
index find( obj ) if ( index gt 0 )
listindex list--num Does not preserve
order! Preserve order move items up!
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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 Different
signatures, different methods. public void remove
( Object obj )
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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. How many are removed? Is it efficient?
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Method RemoveAll
// Removes all objects from list that equal
obj public int removeAll( Object obj ) int
count 0, index find( obj ) while ( index
gt 0 ) listindex list--num
count index find( obj )
return count The user will know how many have
been removed. Not 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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Public Search Method

• Return Index?
• No!
• Boolean method returns true or false
• Integer count method number of time in the bag
• Reference to one element in the bag that equals
  obj

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Public Search
Boolean method returns true or false What should
the name be? theBag.???( obj ) theBag.contains(
obj )! public boolean contains( Object obj )
return find( obj ) gt 0 Dont know where it
is. Dont know number of times. But its in the
bag.
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Method Count
Integer count method number of time in the
bag public int count ( Object obj ) int
numTimes 0 for (int i 0 i lt num i )
if (listi.equals( obj )) numTimes
return numTimes Is it good?
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Method Count
Integer count method number of time in the
bag public int count ( Object obj ) int
numTimes 0 for (int i 0 i lt num i )
if (listi.equals( obj )) numTimes
return numTimes
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Method Count
public int count ( Object obj ) int numTimes
0 while ( find( obj ) gt0 ) numTimes
return numTimes Will it terminate?
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Method Locate
Reference to one element in the bag that equals
obj public Object locate( Object obj ) int
pos find( obj ) if ( pos gt 0 )
return listpos return null Is it
useful? Is listpos the same as obj? Depending
on method equals.
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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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Object Class and Method equals

• Object class has a method equals testing
• Every class is a sub-class of Object and inherits
  method equals
• Most likely, method equals has been overridden
• Example class Student overrides equals to test
  the same ID
• obj has only ID set when calling locate
• public Object locate( Object obj )

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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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Debugging

• Break point
• Where you want to debug
• Step over
• To the next statement
• Step into
• To inside the method being called
• Method call
• As one statement by Step over
• Without method call
• Step into the same as Step over
• Continue
• To next break point

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Debugging

• See the value of a variable
• Scope
• Local variables
• Watches
• Run/Evaluate Expression
• Mouse over