Classes, Objects & Methods Flashcards
Class Syntax
class Name {
}
When is a main method required in a class?
If the class is the starting point of you program.
What types of applications don’t require a main method?
Applets
How do you access instance variables from an object?
object.variable
How does the Java compiler sort class definitions?
It puts each class into its own .class file.
Is it necessary for classes to be in the same source file?
No.
Do the contents of the variables in one object differ from another?
Yes, each instance of a class stores its own contents.
Object Declaration Syntax
object Name = new object();
What does the new operator do?
dynamically allocates memory for an object and returns a reference to it.
Reference Variables
Variables referring to objects.
Vehicle car1 = new Vehicle(); Vehicle car2 = car1;
Are car1 and car2 referencing the same or different objects?
Same
What are methods used for?
Manipulating and providing access to data inside classes.
What method begins execution of a program?
The main method
public static void main(String []args)
{
}
Method Syntax
type name(param) {
}
When is the method Return type void?
If the method doesn’t return a value.
How can you cause the immediate termination of a void method prior to its ending brace? What happens to program control?
Return;
Program control returns to the caller.
How to return a value in a method?
return value;
What methods won’t return values?
Void methods
What method will initialize an object, provide initial values to instance variables & perform other startup procedures?
A constructor
What do you name a constructor?
The same name as its class
What return type should a constructor have?
It has no return type
Do all classes have constructors?
Yes, even if not defined, due to a default constructor in the Object class that initializes all member variables to their default values.
What are the default values of all member variables?
Zero, null & false
Can you add parameters to constructors?
Yes
What does garbage collection do?
Reclaims objects automatically
When is memory occupied by an object released?
When no references to it exist
Under what two conditions will garbage collection run?
There are objects to recycle
There is a need to recycle them
What method is used to ensure an object terminates cleanly?
Finalize()
When is finalize() called? Who calls it?
Java Runtime calls finalize() just before it recycles the object.
What do you include in a finalize() method?
Specify actions that must be performed before the object is destroyed.
What implicit argument exists in a method as a reference to the invoking object?
this
What distinction does this.variable clarify?
When the name of a parameter or local variable is the same as the name of an instance variable. “this” provides access to the hidden instance variable.
Instance variable vs local variable
Local variables are declared in the method or block
Instance variables are declared in the class. They always have a default value.
Aliasing
When one object reference is assigned to another. The address is copied, not the object itself, so it’s a different name for the same object.
Can an object reference refer to nothing?
Yes, null is a reference to nothing.
