Classes and Objects Flashcards
1) Classes as Data Types
A class is basically a data type that can hold both d____ and m_______!
data
methods
2) You can see that there are two aspects to a class:
1: The d_____ that it holds;
2: The t_______s it can perform.
data
tasks
3) Objects
In order to use the methods of a class, you need to create an o__________ of that class.
e.g. as we have been doing in the test classes.
object
4) It’s useful to think of a class as a t____________ from which objects are generated.
an object refers to an individual i_______ of that class.
template
instance
5) Object-oriented programming consists of defining one or more classes that may i_______ with each other.
interact
6) The process of creating an object is called i_______________.
To create an object we use a very special m_________ of the class called a c____________
instantiation
method
constructor
7) The constructor method always has the same n________ as the class.
e.g. Oblong myOblong;
A constructor does NOT r_______ a v_________!
The function of the constructor is to reserve some space in the computer’s m________ to hold the required object.
The new object is stored in a d__________ memory location and the object reference holds the memory address.
name
return a value
memory
different
8) Encapsulation
Encapsulation is the technique of making attributes (variables ,etc) accessible ONLY to the m________ of the same class.
This is a key feature of object-oriented languages.
Encapsulation protects the data in the class by making sure that no program can assign values to the attributes d_______.
methods
directly
9) null
In Java, when a reference is first created without assigning it to a new object in the same line, it is given a special value of null; a null value
indicates that no s______ is allocated.
e.g.
Oblong myOblong; // at this point myOblong has a null value, it is simply a name for a location in m________
myOblong = new Oblong(5.0, 7.5); // create a new Oblong object with length 5.0 and height 7.5
storage
memory
10) What is the key advantage of object-oriented programming over structured programming?
11) What are the differences between primitive data types and object data types?
12) How does a new object affect memory space?
13) How many ways can you create a string object?
14) What is parameter passing by reference?
15) The String Class
Strings are in fact o______ created from a s_____ class!
objects
string
16) The String Class
Java actually allows us to declare a string object in the same way as we
declare variables of s________ type such as int or char.
e.g. int car; (variable declaration)
String name; (variable declaration)
String city; (object declaration)
simple
17) The String Class
Can we do this?
String str;
Str = new String();
Yes
18) The String Class
Can we do this?
String str = new String();
Yes
19) Can we give a value to the string at the time we create it?
e.g.
String str = new String(“Hello”);
Yes! We can.
A faster way of doing the same thing is by typing:
String str = “Hello”
20) Methods of the String class
There are many useful methods in the string class.
Name three:
One of these methods is: .substring(1, 4)
When we call the substring method, we are asking for a certain range of characters, in this case, we want to know the characters from index positions 1 to 4
toLowerCase
toUpperCase
charAt
length
21) Comparing Strings
When comparing two objects, such as Strings, we should do so by using a method called
equals.
We should not use the e_________ operator (==); this should be used for comparing primitive types only.
equality
22) Comparing Strings
If, for example, we had declared two strings, firstString and secondString, we would compare these in, say, an
if statement as follows:
if(firstString.equals(secondString))
{
// more code here
}
What would happen if we used == instead of using ‘equals’?
We would get an error as all you are doing is finding out whether the objects occupy the same address space in memory,
not comparing the actual value of the string attributes of the objects.
23) Can an object of type String can also be used within a switch statement?
Yes
We can use it to check to see if it is equal to one of several possible String values.
e.g.
import java.util.Scanner;
public class StringCheckWithSwitch
{
public static void main(String[] args)
{
Scanner keyboard = new Scanner (System.in);
String symbol;
// get symbol from user
System.out.println(“Enter the symbol(square/circle/triangle)”);
symbol = keyboard.next();
// use String object in switch
switch(symbol)
{
case “square”: System.out.println(“ATTACK”); break;
case “circle”: System.out.println(“BLOCK”); break;
case “triangle”: System.out.println(“JUMP”); break;
default: System.out.println(“Invalid Choice”);
}
}
}
