CS5303-Computer Science I (Java II)

Java Classes:

Use a qualifier, a class keywords, an identifier, and a pair of {}

public class Hello{
   public Hello(){
   public int myInt;
   private float myFloat;
   //This is a constructor
   }
}

Whenever a class is instantiated, meaning memory is allocated, the constructor is called.
The constructor in Java has the same name as the class, and no return type.
One of the primary uses of a constructor is the initialization of member variables.
Like a C structure, a Class can contain different fields of data.
These fields can be made “public” or “private”
The same as C++, private data members cannot be accessed without using a function.
Typically, the private data members have a “get” function to get the data.

    int getData()

And a set function in order to assign the data.

void setData(int  myParameter)

Collection Data Types

• Vector-A self-expanding linked list.
Deprecated and obsolete.
• HashTable-know this one for the future!
Deprecated and obsolete. (in Java)
• Enumeration-Vectors and other types turn into an enumerated series.
Not used so much anymore
• ArrayList-acts like an array, with a get function

Inheritance:

An inheritance means the new class contains all the accessible abilities and traits of its parent class
The parent class is the superclass
The child class is the subclass
protected Data Members:

Protected Data Members:

*Not public, not private, but protected

Protected data members
Private data members are not shared between superclass and subclass
Public data members are shared between superclass and subclass
Protected data members are shared between subclass, superclass, and classes of the same package.

Sample code:(keyword: Extend)

JAVA(tips)：

• Every scalar/atomic/basic value in Java is a basic value
• 5, 3.14159, are numbers/literals/values
• Every class in Java is “instantiated” into an object
• Every object is also a memory area
• Every object variable in Java behaves a pointer reference.
• This has complications:
• A basic assignment between objects “=“, only copies the address
• This is a Shallow Copy, only the address is copies
• A more complex assignment uses a “copy constructor”
• This is a Deep Copy, every field must be assigned appropriately

C++ VS Java：

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speed of C++ & Java

C, C++ create code for an architecture
Java creates code for a Virtual machine.
Since the Java runs on the virtual machine, by its nature, it will always be slower than C++.
Optimization makes this go faster and faster, but always just a little lag.
C++ is faster than Java