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Monday, March 10, 2008
Sunday, March 9, 2008
CSE Lectures 22/Feb/2008 to 27/Feb/2008 Part 2
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CSE Lectures 22/Feb/2008 to 27/Feb/2008 Part 1
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CSE Lecture 6/Feb/2008
Mutators and Accessors in Compositions
-avoid privacy leaks
-make defensive copies whenever mutable objects are passed into or out of the composition. No changes are needed for immutable objects.
Mutator
-create a copy of the external object and start that in our object's attribute.
Accessor
-create a copy of the objects attribute and return that copy.
Constructor
-just like the mutator.
Copy Constructors of Compositions and Aggregates
-"deep copy" --> respect the semantics of the internal objects.
-composition: copy constructor also creates new copies of all internal mutable objects.
-aggregate: only copy references, do not create new copies of internal objects.
Arrays
-Array is similar to ArrayList
- a list of objects stores by index
- all objects of the same type
Array Syntax (starting with primitives)
e.g. a list of 5 integers: int[] x = new int[5]; //creates an empty array of 5 integers.
x.length gives you the length of the array (5 in this case)
e.g. I want to store the int 1024 in the first element of the array.
x[0] = 1024; //note that array indices, like ArrayList, start at zero.
Say you want to get the third element in the array and store it in a separate int.
int y;
y = x[2];
Arrays can be initialized at declaration.
int[] x = {1024,345,-2,123,81};
-avoid privacy leaks
-make defensive copies whenever mutable objects are passed into or out of the composition. No changes are needed for immutable objects.
Mutator
-create a copy of the external object and start that in our object's attribute.
Accessor
-create a copy of the objects attribute and return that copy.
Constructor
-just like the mutator.
Copy Constructors of Compositions and Aggregates
-"deep copy" --> respect the semantics of the internal objects.
-composition: copy constructor also creates new copies of all internal mutable objects.
-aggregate: only copy references, do not create new copies of internal objects.
Arrays
-Array is similar to ArrayList
- a list of objects stores by index
- all objects of the same type
Array Syntax (starting with primitives)
e.g. a list of 5 integers: int[] x = new int[5]; //creates an empty array of 5 integers.
x.length gives you the length of the array (5 in this case)
e.g. I want to store the int 1024 in the first element of the array.
x[0] = 1024; //note that array indices, like ArrayList, start at zero.
Say you want to get the third element in the array and store it in a separate int.
int y;
y = x[2];
Arrays can be initialized at declaration.
int[] x = {1024,345,-2,123,81};
Monday, February 4, 2008
CSE Lecture 4/FEB/08
Note: See the previous lectures notes for the majority of this lectures contents.
Defensive Copying and Privacy Leaks
Composition: external interference with the inner workings of the class are undersirable.
Aggregates: external changes are OK.
The method of Copy Constructors (previous lectures) is called defensive copying.
Defensive Copying and Privacy Leaks
Composition: external interference with the inner workings of the class are undersirable.
Aggregates: external changes are OK.
The method of Copy Constructors (previous lectures) is called defensive copying.
CSE Lecture 1/FEB/08
Collections
-A collection is an aggregate(or composition) in which more than one of each type is allowed.
-The number required is not known in advance.
e.g. Portfolio --> collection of Investments
-We have already seen HashMap from SingletonPerState
Collection Constructors
-Best way: create an empty collection object in the constructor.
-Also, provide a public add() method for loading objects into the collection. This method generally returns a boolean: false if it fails, true otherwise.
Collection Objects - 3 Types
Lists - objects in order, duplicates are OK
Sets - order does not matter, duplicates are not allowed.
Maps - objects are associated with keys.
See code for Portfolio
Iterators and Iterable
-Iterator and Iterable are interfaces.
-A class implementing an interface must implement all the methods specified in the interface exactly. This means the same return type, same name (case-sensitive), same number, order, and types of paramters.
--> MyClass implements MyInterface
public class MyClass implements MyInterface
{
.
.
.
}
The Iterator interface allows a method to take some action on each element in a collection. It contains a method that returns the collection's Iterator --> repackaging the collection for iterator operations.
See Rest of Portfolio code including getValue() method.
-A collection is an aggregate(or composition) in which more than one of each type is allowed.
-The number required is not known in advance.
e.g. Portfolio --> collection of Investments
-We have already seen HashMap from SingletonPerState
Collection Constructors
-Best way: create an empty collection object in the constructor.
-Also, provide a public add() method for loading objects into the collection. This method generally returns a boolean: false if it fails, true otherwise.
Collection Objects - 3 Types
Lists - objects in order, duplicates are OK
Sets - order does not matter, duplicates are not allowed.
Maps - objects are associated with keys.
See code for Portfolio
Iterators and Iterable
-Iterator and Iterable are interfaces.
-A class implementing an interface must implement all the methods specified in the interface exactly. This means the same return type, same name (case-sensitive), same number, order, and types of paramters.
--> MyClass implements MyInterface
public class MyClass implements MyInterface
{
.
.
.
}
The Iterator interface allows a method to take some action on each element in a collection. It contains a method that returns the collection's Iterator --> repackaging the collection for iterator operations.
See Rest of Portfolio code including getValue() method.
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