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Association / Aggregation / Composition and inheritance
Association
Relationship where all object have their own lifecycle and there is no owner.
Ex: Airplane and passengers. No ownership between the objects and both have their own lifecycle. Both can create and delete independently
AggregationSpecial form of Association where all object have their own lifecycle but there is ownership ( Has a relationship) and child object can not belongs to another parent object.
Ex: Department and teacher.
A single teacher can not belongs to multiple departments, but
if we delete the department teacher object will not destroy.
Composition
Special form of Aggregation . Child object dose not have their lifecycle and if parent object deletes, all child object will also be deleted (ownership). Ex : Person and hands.
Inheritance : ”is” relationship
An employee is a person
• Association No ownershipOwn lifecycle
• AggregationOwnership ( has a..)Own lifecycle
• CompositionOwnership (composed of ..) No Own lifecycle
• InheritanceIs relationship
Association
8
Student * 5..60 Take Teach 0..3 1
Teacher Faculty Course
public class Student {
/** Data fields */
private Course[]
courseList;
/** Constructors */
/** Methods */
}
public class Course {
/** Data fields */
private Student[]
classList;
private Faculty faculty;
/** Constructors */
/** Methods */
}
public class Faculty {
/** Data fields */
private Course[]
courseList;
/** Constructors */
/** Methods */
}
An association is usually represented as a data field in the class.
Representing Aggregation/composition in Classes
An aggregation / composition relationship is usually represented as a data field in the aggregated class.
9
public class Name {
/** Data fields */
/** Constructors */
/** Methods */
}
public class Person {
/** Data fields */ private Name name;
private Address address;
/** Constructors */
/** Methods */
}
public class Address {
/** Data fields */
/** Constructors */
/** Methods */
}
Name Address Person
Composition Aggregation
Inheritance
Inheritance models the is-an-extension-of relationship between two classes.
10
Person Faculty
public class Faculty extends Person {
/** Data fields */
/** Constructors */
/** Methods */
}
(A) (B)
Borrowing Loans
11
Name BorrowerPersonLoan Address
Loan
Borrower -loan: Loan +Borrower() +Borrower(name: Name, address: Address) +getLoan(): Loan +setLoan(loan: Loan): void +toString(): String
Address -street: String -city: String -state: String -zip: String +Address() +Address(street: String, city: String, state: String, zip: String) +getStreet(): String +getCity(): String +getState(): String +getZip(): String +setStreet(street: String): void +setCity(city: String): void +setState(state: String): void +setZip(zip: String): void +getFullAddress(): String
Defined in Example 6.7
Person -name: Name -address: Address +Person() +Person(name: Name, address: Address) +getName(): Name +seName(name: Name): void +getAddress(): Address +setAddress(address: Address): void +toString(): String
Name -firstName: String -mi: char -lastName: String +Name() +Name(firstName: String, mi: char, lastName: String) +getFirstName(): String +getMi(): char +getLastName(): String +setFirstName(firstName: String): void +setMi(mi: char): void +setLastName(lastName: String): void +getFullName(): String
