Chapter 1- Variables and Data Types in Java Programming

Just like we have some rules that we follow to speak English (the grammar), we have some rules to follow while writing a Java program. The set of these rules is called syntax.                [It’s like Vocabulary and Grammar of Java :)]

• Variables

A variable is a container that stores a value.

This value can be changed during the execution of the program.

Example: 

int number = 8;

(Here, int is a data type, number is the variable name and 8 is the value that it contains/stores)

• Rules for declaring a variable name

We can choose a name while declaring a Java variable if the following rules are followed:

• Must not begin with a digit. (E.g. 1arry is an invalid variable)
• Name is case sensitive. (harry and Harr are different)
• Should not be a keyword (like Void)
• White Space not allowed. (int Code With Harry is invalid)

Can contain alphabets, $character, _character, and digits if the other conditions are met.

• Data Types

Data types in Java fall under the following categories

• Primitive Data Types (Intrinsic)
• Non-Primitive Data Types (Derived)

• Primitive Data Types

Java is statically typed i.e. variables must be declared before use.

There are 8 primitive data types supported by Java:

byte     ➼   •value ranges from -128 to 127

                  •takes 1 byte 

                  •default value is 0

short    ➼   •value ranges from -(216)/2  to  (216)/2 - 1

                   •takes 1 byte 

                   •default value is 0  

int        ➼    •value ranges from -(232)/2 to (232)/2 - 1

                    •takes 2 byte 

                    •deafault value is 0

 float      ➼    •value ranges from (See Docs)

                    •takes 4 byte

                    •deafault value is 0.0f

long      ➼    •value ranges from -(264) /2 to (264)/2 - 1

                    •takes 8 byte 

                    •default value is 0

double   ➼  •value ranges from (See Docs)

                   •takes 8 byte 

                   •deafault value is 0.0d

char       ➼  •value ranges from 0 to 65535(216 - 1)

                    •takes 2 byte 

                    •default value is 

boolean ➼   •value can be true or false

                    •size depend on JVM

                    •default value is false

Quick Quiz: Write a Java program to add three numbers :

package com.company;
public class Main {
    public static void main(String[] args) {
   // write your code here
        System.out.println("Sum of Three Numbers");
        int num1=5;
        int num2=10;
        int num3=15;
        int sum= num1+num2+num3;
        System.out.println(sum);
    }   
    /*
    Output :    
    30   
    */ 

• How to choose data types for our variables

In order to choose the data type we first need to find the type of data, we want to store. 

After that, we need to analyze the min & max value we might use.