JAVA

USAGE

DEFINITION

INTERFACE:

• methods without their bodies
• constant fields - implicitly public, final, and static
• classes implementing an interface should implement all their methods!
• a class can implement multiple interfaces

JAVA

Interface:

• can be extended by another interface
• can be implemented by a class
• can be passed as parameter to a method -> if an interface type is required as an argument, you can pass any object whose class implements this interface

ABSTRACT class:

• can be extended by another class

ABSTRACT class can have:

• data member,
• abstract method
• non-abstract method
• constructor
• cannot be instantiated
• a class extending an abstract class shouldn't extend all its methods
• a class can only extend only one single [abstract] class

1 - N: 1 interface can EXTEND multiple interfaces

INTERFACE

1 - N: 1 class can IMPLEMENT multiple interfaces

Abstract CLASS

MAIN

1 - 1: 1 class can EXTEND one single other class

1 - N: 1 class can BE EXTENDED by multiple classes

Static CLASS

CLASS

ABSTRACTION

STATIC:

• @class level, not associated with an instance of a class
• static values:
• passed by reference

STATIC class:

• can be used by other class or in main
• variables and methods are accessed only at CLASS level:
• eg: Integer.parseInt()

CANNOT

1 - N: 1 class can be INSTANTIATED by multiple objects

OBJECT

OBJECTS:

• CREATE - to instantiate objects through constructors:
• new - key word:
• allocates the memory described by the class, and runs the constructor
• returns a reference to the allocated memory
• apply methods defined in the class definition on the objects:
• RETRIEVE info: sufragerie.scaun.getCuloare()
• UPDATE info:

CLASSES - contains:

• variables
• primitive types
• ENUM / finals
• reference types (classes)
• Date / String / Integer or
• custom classes defined by us
• collections
• methods - contains all logic & operations
• takes parameters:
• none ()
• a primitive type, an object, an interface
• returns a result:
• void
• a primitive type, an object
• eg:
• constructors - to instantiate an object
• getter, setter
• other operations