Java Syntax, Java Conventions,
CSE 115 Conventions (Part 3)
CSE 115
Spring 2006
February 6, 8 & 10, 2006
XX - References
Declaring an instance variable creates a
reference.
All references are initially null.
We assign a value to a reference using the
assignment operator
XXI – Assignment Operator
=
Takes the value on the right and assigns it
to the variable on the left:
_varName = new Object();
Review of Composition
Declare an instance variable
Create an instance of the subpart
Assign the instance to the instance
variable
Note that steps two and three above
actually happen in one line of code.
ClassA has a ClassB
public class ClassA {
private ClassB _classB;
public ClassB() {
_classB = new ClassB();
}
}
XXII – Sending Messages
Asking/telling an object to do something,
or asking it to perform one of its
capabilities.
Capabilities are methods inside our class
definition.
In code, we would be performing a method
call/method invocation.
Syntax of a Method Call
instanceName.methodName();
• Q: What is the name of the () and what
are the () used for in a method call?
Four Main Parts of a Method
Sender
Receiver
Return Type
Parameters
Describe the purpose of each of these and
what they correspond to in code.
Cardinality
The number of a certain type of
relationship between objects.
An Applet can have 5 BouncingBalls. That
means there are 5 instances of the “has-a”
relationship present.
Association Relationship
“knows a” relationship
In UML, represented by an arrow ( → )
In code:
Declare an instance variable of the associate.
In constructor, accept a parameter whose type
is the same as that of the associate
Assign the value of the parameter to the
instance variable
Dog knows a Tree
public class Dog {
private Tree _tree;
public Dog(Tree tree) {
_tree = tree;
}
}