WEEK 2 - OBJECT ORIENTED JAVA PROGRAMS AND ARRAYS REVIEW

Question 1

What are programs made of?

Answer 1

Objects

Question 2

What defines objects?

Answer 2

Classes

Question 3

What is a class?

Answer 3

A class defines what objects look like and are things implemented during the design time.

They are defined through:
- Using the class keyword
- All Java code consists of classes
- All Java code is “part of” some class
- Big programs can have many classes
- Think of a class as a recipe to create objects

Question 4

When are objects created and what defines them?

Answer 4

Objects are created from classes at run time.

What defines an object?
- Each object’s properties are defined by the class it was created from
- Many objects can be made from one class

Question 5

What is in a class?

Answer 5

Information or data (what the objects will be made of) and functionality (what the object will do)

1. The elements of a class that contain information (data) are called variables. The variables defined for the whole class are called fields.
2. The elements of a class that execute commands to implement functionality are called methods.

Question 6

What is the syntax for a field variable?

Answer 6

<visibility> <type> <name>;

* Visibility modifier is optional
</name></type></visibility>

Question 7

How to declare a field variable and initialize it in a combined statement

Answer 7

<visibility> <type> <name> = <value>;
</value></name></type></visibility>

Question 8

What is the automatically initialized value given to field variables?

Answer 8

Integer, floating point and char = 0 or 0.0.

Boolean = false.

String and any class = null.

Question 9

What are user-defined types?

Answer 9

User-defined types can be predefined by the class libraries that are provided by the Java runtime. Classes are user-defined types.

Question 10

What is the . (dot) operator?

Answer 10

An accessibility operator used to access an element that is defined inside an object you must use the object variable followed by the . (dot) operator.

Question 11

What are attributes?

Answer 11

Information in field variables.

Example.
public class Circle {
private double radius = 10.0;
}

Question 12

An object is made of ________?

Answer 12

Fields.

Question 13

What are fields?

Answer 13

Variables declared directly in the class definition block (not in a method).

Question 14

Create an example of a method

Answer 14

public void methodName() {
}

Question 15

Create an example of a method with one parameter

Answer 15

public void methodName(dataType paraName) {
}

Question 16

Create an example of a method with two parameters

Answer 16

public void methodName(dataType paraName, dataType paraName) {
}

Question 17

What is a method call statement?

Answer 17

A method is called using a method call statement which gives
1. The name of the method to be called
2. The list of values to be passed as parameters (without data types!)
3. Each value could be a calculation or expression

Question 18

What are the two “styles” of method call?

Answer 18

1. Without an object variable (calling another method of the same class)
2. With an object variable (calling a method of that object)

Question 19

How does a method return a value it calculated to the caller?

Answer 19

Using the return statement.

Question 20

What is the syntax of a return statement?

Answer 20

<visibility> <dataType> <methodName> (dataType param?, ...) {

return methodExpression;

}

Ex.
public int addNumbers(int num1, int num2)
{
return num1 + num2;
}
</methodName></dataType></visibility>

Question 21

What are accessor (getter) methods?

Answer 21

Accessor methods return the value of a private variable, allowing other classes access to that stored variable.

Question 22

What is the syntax for an accessor (getter) method?

Answer 22

<visibility> <dataType> <getMethodName> () {
return variableName;
}

Example.
public String getFirstName() {
return _firstName;
}
public double getRadius() {
return _radius;
}
</getMethodName></dataType></visibility>

Question 23

What are mutator (setter) methods?

Answer 23

Mutator methods reset the value of a private variable. This gives other classes the ability to modify the value stored in that variable without having direct access to the variable itself.

Question 24

What is the syntax for a mutator method?

Answer 24

<visibility> <dataType> <setMethodName> (dataType paramName) {
variable = newVariable;
}

public void setFirstName(String newName) {
_firstName = newName;
}
public void setRadius(double radius) {
_radius = radius;
}
</setMethodName></dataType></visibility>

Question 25

What is a constructor?

Answer 25

A constructor is a special method whose role is to initialize the object when an object is created.

The constructor is called ONLY when an object is created (‘new’).

Name of the constructor is ALWAYS the same as the name of the class.

A constructor is normally used to initialize field variables defined by the class.

Question 26

What are the four rules of constructors?

Answer 26

1. Constructors must have the same name as the class itself.
2. Constructors do not have a return type – not even void.
3. Constructors are invoked using the new operator when an object is created.
4. Constructors play the role of initializing objects.

Question 27

What is a no-arg constructor?

Answer 27

A constructor with no parameters.

Question 28

What is a default constructor?

Answer 28

A constructor that has no parameters.

A default constructor is automatically generated if no other constructors are defined for a given class/

Question 29

What is method overloading?

Answer 29

Method overloading means more than one method with the same name.

Any method can be overloaded.

The list of parameters must be different in each method.

Question 30

What is a static method?

Answer 30

Methods that are shared by all objects of the same class, and are independent from any particular object (instance).

Question 31

What are static fields?

Answer 31

Static field variables are shared by all objects of the same class,
and are independent from any particular object (instance).
There is only one copy of a static field variable.