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Lists
Chapter 4
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Chapter Contents
Specifications for the ADT List• Redefining the Specifications
Using the ADT List
Using a List Is Like Using a Vending Machine
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Specifications for the ADT List
A list provides a way to organize data
A to-do list, address list, grocery list etc…
ADT list must be considered in general, not necessarily a list of strings. It can contain any type of objects.
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Specifications for the ADT List
Operations on lists• Add new entry – at end, or anywhere• Remove an item• Remove all items• Replace an entry• Look at any entry• Look for an entry of a specific value• Count how many entries• Check if list is empty, full• Display all the entries
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Specifications for the ADT List
To specify an ADT list• Describe its data( A collection of objects in a specific
order and having the same data type, the number of objects in the collection.)
• Specify the operations
ADT does not indicate how to store the data or how to implement the operations.
In contrast, a data structure is an implementation of an ADT within a programming language.
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Example
The effect of ADT list operations on an initially empty list.
Convenient way of identify a particular entry is by the entry’s position within the list. Position-oriented ADT
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Potential Problem Operations
add, remove, replace, getEntry work OK when valid position given
• remove, replace and getEntry not meaningful on empty lists
• A list could become full, what happens to add?
• What else operations may cause problems?
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Possible Solutions
Assume the invalid situations will not occurIgnore the invalid situationsMake reasonable assumptions, guess at the client’s intention. act in predictable wayReturn a signal or Boolean value indicating success or failure of the operationThrow an exception
The documentation for ADT should describe these possible solutions.
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Redefining Specifications
A first draft of an ADT specifications may ignore potential problems• Simplifies the first draft
Concentrate on details after major portions of specifications written• Makes the specifications complete
After writing specifications, • Write Java interface for its operations• Java interface can be used for class to
implement the ADT
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Generic Types Within an Interface and Class
public interface Pairable<S>
{
public void setPairs(S firstItem, S secondItem)
}
A class that implements this interface could begin with the statement
public class OrderedPair<T> implements Pairable<T>
A class to represent pair of objects of the same type. Since each pair can be of any class type, we used a generic type in the definition of the class.
The method setPair has parameters of a generic type. Imagine an interface Pairable that declares this method.
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ListInterface/** An interface for the ADT list.
* Entries in the list have positions that bewgin with 1.*/
public interface ListInterface<T>
{
/** Task: Adds a new entry at a specified position within the list. The list’s size is
* increased by 1.
* @param newPosition an integer that specifies the desired position of the new entry
* @param newEntry the object to be added as a new entry.
* @return true if the addition is successful, or false if either the list is full, newPosition <1, or newPosition > getLength() +1 */
public boolean add( int newPosition, T newEntry);
How to write the comments for method remove?
public T remove( int givenPosition);
}
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Using the ADT List
A list of numbers that identify runners in the order in which they finish a race
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Using the ADT List
AList implements interface ListInterface.
AList implements interface ListInterface.
public class ListClient
{ public static void main(String[] args) { testList(); } // end main
public static void testList()
{ ListInterface<String> runnerList = new AList<String>(); // has only methods// in ListInterface
runnerList.add("16"); // winner runnerList.add(" 4"); // second placerunnerList.add("33"); // third placerunnerList.add("27"); // fourth placerunnerList.display();
} // end testList
} // end ListClient
The data type of runnerList is ListInterface<String>. This declaration obliges runnerList to call only methods in the interface. If the data type was Alist<String>, what methods are available to runnerList?
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Java Class Library: The Interface List
The standard package java.util contains a list interface – called List
Methods providedpublic boolean add(Object newEntry)
public void add(int index, Object newEntry)
public Object remove(int index)
public void clear()
public Object set(int index, Object anEntry) // like replace
public Object get(int index) // like getEntry
public boolean contains(Object anEntry)
public int size() // like getLength
public boolean isEmpty()
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A List Interface is Like a Vending Machine
A vending machine.
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A List Interface is Like a Vending Machine
Observations about vending machines
Can perform only tasks shown on interface
Must understand the tasks
Cannot see inside the machine
Can use the machine even though don’t know what happens inside
If inside of machine replaced with new improved version• Interface remains unchanged• Customer uses machine in same way as before
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A List Interface is Like a Vending Machine
Observations about clients and List ADTClient can perform only operations from the ADT ListClient must adhere to specificationsClient cannot access data without an ADT operation. Encapsulation hides the data representation within the ADTClient can use the list – even though unable to access entries directly. Don’t need to know how the data is stored. If implementation is changed, client still uses list in same way as before
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Exercise
Suppose that you have a list that is created by the following statement:
ListInterface<Double> quizScores = new AList<Double>(); Imagine that someone has added to this list the quiz
scores received by a student throughout a course. The professor would like to know the average of these quiz scores, ignoring the lowest score.a. Write Java statements at the client level that will find and remove the lowest score in the list.b. Write Java statements at the client level that will compute the average of the scores remaining in the list.
