Data Types, Variables, Java Reserved Words

Study Java Programming With Script With Me

Java

Data Types

It is a set (range) of values which has similar characteristics.
It is a collection of data with a value which has a meaning and its characteristics.
It determines the type of the data which is held by a variable.

Example:

int x;

Where, ‘int’ is an integer data type and, x is a variable.

In the above example it shows that the variable ‘x’ can store only the integer type value.

Data Types	Memory Size
Char	2 bytes
Boolean	1 bit
Short	2 bytes
Int	4 bytes
long	8 bytes
Float	4 bytes
Double	8 bytes

Example Program:

package Sample;
public class DataTypes {
       public static void main(String[] args)
       {
            int i = 5; // integer
            float f = 5.99f; // floating point number
            char c = 'A';  // character
            boolean b = true;  // boolean
            String Text = "ScriptWithMe";  // String   
            System.out.println(i);
            System.out.println(f);
            System.out.printl(c);
            System.out.println(b);
            System.out.println(Text);
       }
}

Output:

5
5.99
A
true
ScriptWithMe

Variables

To store values in memory, we need to reserve some space which is done using a variable.
During the execution of a program, we can modify the value of a variable.

TYPES OF VARIABLES:

Local Variables.
Instance Variables.
Static Variables.

LOCAL VARIABLE:

If a variable is defined within a block or constructor, or method, then it is known as a Local Variable.
Its initialization is mandatory.

Example:

Output:

INSTANCE VARIABLE:

If a variable is declared inside a class when an object of the class is created and destroyed when an object is destroyed, then it is known as Instance Variable.
It is a non-static variable.
It is declared in a class but not inside the method, block or constructor.
Unlike local variables, here, we can use an access specifier along with an instance variable.
It always gets a default value.
Its initialization is not mandatory.
It cannot be reinitialized directly with a class.
It can be accessed only by creating objects.
Each object has its separate copy of the instance variable.

Example:

Output:

STATIC VARIABLE:

Its declaration is similar to an instance variable, and the only difference is that the static variables are declared using the keyword “static”.
It is created at the beginning of program execution and destroyed automatically when execution end.
Its initialization is not mandatory.
We can only have one copy of the static variable per class.
As static variables are common to all the class objects, changes will be reflected in other objects.
We need not create an object of that class for accessing the static variable, and we can simply access the variable as className.variableName

Example:

Output:

Java Reserved Keywords

There are 49 reserved keywords defined within Java.
These 49 keywords can’t be used as names for a variable, class, or method.

abstract	continue	goto	package	synchronized
assert	default	if	private	this
boolean	do	Implements	protected	throw
break	double	import	public	throws
byte	else	instanceof	return	transient
case	extends	int	short	try
catch	final	interface	static	void
char	finally	long	strictfb	volatile
class	float	native	super	while
const	for	new	switch
Java Reserved words

The const and goto keywords are reserved words but not used.
In addition to the above keywords, Java also reserves the following: true, false, and null. These are values defined by Java, and these words are not used for the names of variables, classes and so on.

Who is the course for?

Prerequisites before starting this course:

Before entering into this course you should have the basic understanding of how computer technology works.
If you don’t have any experience in Java or any other programming language then this course is for you.
If your intermediate level of knowledge in Java programming and you want to enhance your Java skills to advance level then this course is for you.
All you need is just any of the one device mobile, laptop, or PC and internet connection.

Questions 🙵 Answers.

Lesson 1 - Know Your Audience

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