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Agenda• Announcements
– Cell phones / laptops off & away / Name signs out• Last time
– Composition relationship– Lifetime/Scope
• Today– Unified Modeling Language (UML)
• composition
– Naming conventions– Methods
whole/part creation in code(elaborated)
• Whole creates instance of part in its constructor
• In Java code, involves 3 changes to whole class:– Declaration of instance variable of part type– Instantiation of part class in whole class
constructor– Assignment of new part instance to instance
variable
4
Dog – Tail example in Java
package cse115;
public class Dog { private Tail _tail; public Dog() { _tail = new Tail(); }}
UML
Unified Modeling Language
(Class Diagrams)
UML
• Unified Modeling Language– express design without reference to
an implementation language
• For example
Composition in UML
Binary Class Relationships:directional
• binary two classes are involved– source class has code modification– target class does not
• composition– source: WHOLE– target: PART
• in diagram:– line decoration is on source/WHOLE– show only detail that’s needed/desired
package cse115;
public class Dog {
public Dog() {
}
}
package cse115;
public class Tail {
public Tail() {
}
}
package cse115;
public class Dog {private Tail _tail;public Dog() {
_tail = new Tail();
}
}
package cse115;
public class Tail {
public Tail() {
}
}
Naming conventions
• packages: all lower case• classes:
– first character: upper case letter– camel case afterwards
• instance variables– first character: underscore ‘_’– camel case afterwards
• local variables– first character: lower case– camel case afterwards
package lab2;
public class EcoSystem {private example1.Terrarium _t;
public EcoSystem() {_t = new example1.Terrarium();
}
public void addTwoCaterpillars() {example1.Caterpillar c1 = new
example1.Caterpillar();example1.Caterpillar c2 = new
example1.Caterpillar();_t.add(c1);_t.add(c2);c1.start();c2.start();
}}
Constructor definition
Method definition
package lab2;
public class EcoSystem {private example1.Terrarium _t;
public EcoSystem() {_t = new example1.Terrarium();
}
public void addTwoCaterpillars() {example1.Caterpillar c1 = new
example1.Caterpillar();example1.Caterpillar c2 = new
example1.Caterpillar();_t.add(c1);_t.add(c2);c1.start();c2.start();
}}
The scope of an instance variable declaration is the entire class body.
The variable can (and should) be assigned an initial value (initialized)
in…
The variable can be used in any method of
the class.
Here’s a method definition.
Both the constructor and this method are in
the scope of the instance variable
declaration.
The instance variable can (and should) be assigned an initial
value (initialized) in… the constructor.
It can be used in any method in class body.
Method definition syntax
public void addTwoCaterpillars() {example1.Caterpillar c1 = new
example1.Caterpillar();example1.Caterpillar c2 = new
example1.Caterpillar();_t.add(c1);_t.add(c2);c1.start();c2.start();
}
method definition
Method definition syntax
public void addTwoCaterpillars() {example1.Caterpillar c1 = new
example1.Caterpillar();example1.Caterpillar c2 = new
example1.Caterpillar();_t.add(c1);_t.add(c2);c1.start();c2.start();
}
Remember that method definition consists of both a method header a method body.
Method definition syntax
public void addTwoCaterpillars() {example1.Caterpillar c1 = new
example1.Caterpillar();example1.Caterpillar c2 = new
example1.Caterpillar();_t.add(c1);_t.add(c2);c1.start();c2.start();
}
Here’s the method body.
Method definition syntax
public void addTwoCaterpillars() {example1.Caterpillar c1 = new
example1.Caterpillar();example1.Caterpillar c2 = new
example1.Caterpillar();_t.add(c1);_t.add(c2);c1.start();c2.start();
}
The method header begins with an access control modifier, public in this case.
Method definition syntax
public void addTwoCaterpillars() {example1.Caterpillar c1 = new
example1.Caterpillar();example1.Caterpillar c2 = new
example1.Caterpillar();_t.add(c1);_t.add(c2);c1.start();c2.start();
}
return type specification‘void’ is a special return type specification, indicating that no value is returned by the method
Method definition syntax
public void addTwoCaterpillars() {example1.Caterpillar c1 = new
example1.Caterpillar();example1.Caterpillar c2 = new
example1.Caterpillar();_t.add(c1);_t.add(c2);c1.start();c2.start();
}
Next comes the name of the method. Method names follow the same convention as local variables
Method definition syntax
public void addTwoCaterpillars() {example1.Caterpillar c1 = new
example1.Caterpillar();example1.Caterpillar c2 = new
example1.Caterpillar();_t.add(c1);_t.add(c2);c1.start();c2.start();
}
parameter list – empty in this exampleremember: argument list method call
parameter list method definition
Method definition syntax
public void addTwoCaterpillars() {example1.Caterpillar c1 = new
example1.Caterpillar();example1.Caterpillar c2 = new
example1.Caterpillar();_t.add(c1);_t.add(c2);c1.start();c2.start();
}
method body – delimited by braces
Method definition syntax
public void addTwoCaterpillars() {example1.Caterpillar c1 = new
example1.Caterpillar();example1.Caterpillar c2 = new
example1.Caterpillar();_t.add(c1);_t.add(c2);c1.start();c2.start();
}
statements & (local variable) declarations – consists of local variable declarations and statements, which in this case are all method calls.
