Notes
Outline
Packages
Group of related classes.
Specified by package statement.
Fewer restrictions on access among each other;
if class is called public, then it is visible to all classes
if no visibility modifier is specified, it is equivalent to the friend specification from C++, and its visibility is termed as “package visibility” and is somewhere between:
private (other classes in package cannot access it) and
public (other classes outside package can also access it)
A class cannot be private or protected. Only methods & fields are allowed to be declared as such.
Package locations can be specified by the CLASSPATH environmental variables.
The import statement helps to get multiple packages. It saves typing.
Access Restrictions of Methods/Fields
Clients have access to only public methods.
Derived classes have access to public & protected members of the base class.
Classes within the same package have access to protected and package members of the base class.
Public – can be used by anyone .
Package – by methods of the class and in same package.
Protected – by methods of the class and subclasses and in the same package.
Private – only by members of the same class.
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Containers
Powerful tool for programming data structures
Provides a library of container classes to “hold your objects”
2 types of Containers:
Collection: to hold a group of elements e.g., List, Set
Map: a group of key-value object pairs. It helps to return “Set of keys, collection of values, set of pairs. Also works with multiple dimensions (i.e., map of maps).
Iterators give you a better handle on containers and helps to iterate through all the elements. It can be used without any knowledge of how the collection is implemented.
Collections API provides a few general purpose algorithms that operate on all containers.
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