CLASSES AND OBJECTS

Question 1

What code is found within the class body?

Answer 1

 constructors for initializing new objects,
 declarations for the fields that provide the state of the class and its objects
 methods to implement the behavior of the class and its objects.

Question 2

What extra information can be provided at the declaration of the class?

Answer 2

Modifiers such as public, private, and a number of others that you will encounter later.
The class keyword
The class name, with the initial letter capitalized by convention.
The name of the class's parent (superclass), if any, preceded by the keyword extends. A class can only extend (subclass) one parent.
A comma-separated list of interfaces implemented by the class, if any, preceded by the keyword implements. A class can implement more than one interface.
The class body, surrounded by braces, {}.

EG:

class MyClass extends MySuperClass implements
YourInterface {
 // field, constructor, and
 // method declarations
}
• In this scenario, MyClass is a subclass of MySuperClass and implements the YourInterface interface.

Question 3

What are modifiers? And give examples

Answer 3

• A modifier is a keyword placed in a class, method or
variable declaration that changes how it operates and
to what extent it can be accessed.

• abstract
• final
• native
• private
• protected
• public
• static
• strictfp
• synchronized
• transient
• volatile.

Question 4

What are access modifiers?

Answer 4

• The first (left-most) modifier used lets one control what other classes have access to a member field.

 public modifier—the field is accessible from all classes.
 private modifier—the field is accessible only within its own class.

Question 5

What is a method?

Answer 5

A method is a set of code which is referred to by name and can be called (invoked) at any point in a program simply by utilizing the method’s name.

Question 6

What is the structure of a method declaration and method signature and give an example?

Answer 6

• Modifiers—such as public, private, and others you will learn about later.
• The return type—the data type of the value returned by the method, or void if the method does not return a value.
• The method name—the rules for field names apply to method names as well, but the convention is a little different.
• The parameter list in parenthesis—a comma-delimited list of input parameters, preceded by their data types, enclosed by parentheses, (). If there are no parameters, you must use empty parentheses.
• An exception list
• The method body, enclosed between braces—the method’s code, including the declaration of local variables, goes here.

• An example of a typical method declaration is as follows:
public double calculateRectArea(float area, float length,
float width) {
 //calculation comes here
}
• Method signature: This comprises of the two components of a method declaration:—the method's name and the parameter types, e.g. in the above case:
calculateRectArea(float, float, float)

Question 7

What are the guidelines for method naming? And give examples

Answer 7

• By convention, method names should be a verb in
lowercase or a multi-word name that begins with
a verb in lowercase, followed by adjectives, nouns, etc.
• In multi-word names, the first letter of each of the
second and following words should be capitalized

• Example of method names would include:
• add
• addIntegers
• getImage
• getImageData
• compareWith
• setY
• isNull