JAVA Variables Declaring Variables Over writing Variables Data

JAVA Variables Declaring Variables Over writing Variables Data types Displaying contents of a Variable Naming a Variable Strings

What is a Variable? �When a Java program is running, it would need memory storage to store values �RAM is used to store these temporary values �These small memory locations are called variables.

How do Variables work? � As programmers we can create variables that have a particular data type to store values �All the different variables have to have unique names �If we imagine the RAM as a set of pigeon holes, to put a pigeon in its pigeon hole we would need to give the hole a name and then the pigeon/data which it can home must be set/declared.

Example Lets say we need to store three pigeons we need to create two pigeon holes (variables) called P 1 which is set to hole Billy, P 2 set to hold Henry and P 3 to hold Milly. � Billy NOTE: A variable can only hold one value, you cannot have two pigeons in one pigeon hole P 1 Henry P 2 P 3 Milly

Declaring a Variable �Before using a we have to declare/set it � When declaring a variable we must include two aspects; 1. Variable name 2. Variable data type variable_name;

Example �Lets say we want to declare to variables to hole numbers N 2 N 1 NOTE: Type int can only hold integers. We will learn different data types soon. INT int N 1; int N 2;

class Variables. Example { public static void main (String args[]){ //variables are declared The memory locations for three int N 1; variables are created. These can int N 2; only store whole numbers. int tot; //assign values to variables N 1 = 50; Numbers are stored in the N 2 = 13; variables //the total of variables N 1 and N 2 //is stored in tot = N 1 + N 2; Instead of storing a particular value in tot, the sum of N 1 and } N 2 is stored. } Copy this program

What we have … N 1 50 N 2 13 tot 63

Overtyping �If we take the example pf before where we have the following variables 1. N 1 = 50 2. N 2 = 13 � If we change N 1 to hold the number 33 (N 1 = 33) then the integer 50 will be overwritten but 33 and the 50 will be lost

Direct initialisation �We can decide to set a value to the variables as soon as we create them �This �The is call Direct initialisation program would work the same it would just be shorter

class Variables. Example { public static void main (String args[]){ //variables are declared are assigned N 1 and N 2 are declared as int N 1 = 50; and assigned a value int N 2 = 13; immediately. int tot; //the total of variables N 1 and N 2 //is stored in tot = N 1 + N 2; } } Copy this program

Data Types – Integers �The following are examples of integer data types you need to know

Data Types – Real (numbers) �The following are examples of real data types you need to know

Data Types – �The following are examples of some other data types you need to know

Important information �When assigning a value to a character variable, the character to be assigned must be enclosed in single quotes. class Char. Ex { public static void main (String args[]){ char label; label = ‘B’; } } Copy this program

Important information �When assigning a value to a boolean variable, we can only store true or false; these are not to be placed in single quotes. class Boolean. Ex { public static void main (String args[]){ boolean can. Drive; can. Drive=false; } } Copy this program

Displaying Contents of a Variable �We print the contents of a variable using System. out. ptintln() System. out. println(variable_name) �In order to print the contents of a variable it is important that the variable name is not placed inside quotes � If we put the variable name in quotes the name of the variable will appear

Example char letter; letter = ‘C’; System. out. println(“letter”); Output = letter char letter; letter = ‘C’; System. out. println(letter); Output = C

Activity �Go back to the programs we have writing and output the contents of the variables

Giving Variables a Name These are some of the things to remember: �It must start with a lowercase letter, �It cannot be a keyword used in Java, �It must be unique, �It cannot contain blank spaces (use Camel. Case) �It must reflect the contents that it will store

Strings �In some programs we would want to store text � The char data type cannot be used since it can only store one character �We use what is called a String which stores characters, numbers, a mixture of both and also symbols

Example �Lets say we want to store out name String full. Name = “Ruby Borg”; �To output a string we use System. out. print() System. out. println(full. Name); �To combine a String with more text, the + operator is used System. out. println (“The next person is

Activity �Create a program to hold and output your name and class. �Out put should be as follows My name is Ruth Borg I am in form 4 One