This is a five part series

with four goals

We want to explain key Java concepts to

people with very little programming experience

or no programming experience

We want to show the Java syntax

We want to introduce people to the jargon

and at the same time we want to keep everything as brief as possible

because the best way to learn is to do it rather than talk about it

In this video we are going to

talk about the Java type system

as well as variables

So why do we need Java in the first place?

When we make an app or when we write a program

we have to instruct the computer in a language it can understand

But computers speak in

ones and zeros

We don't want to resort to having

to write machine code

or machine language

or type in ones and zeros

into the computer

So we use a programming language

which can easily be translated

into machine code that the computer can understand

and that's Java

There's really four stages to programming

First, we translate our ideas into Java code

Second, we send that code on to the compiler

The compiler is a special program

that takes a look at the Java code

and then sees if it complies with the rules of Java

and general syntax requirements

and if it doesn't; if it spots any errors

the compiler complains and we have to fix those problems

before we can continue

However, if we pass the compiler's scrutiny

the compiler will translate the Java code into something that's executable by the machine

and at this point the program starts to run

This is when we are able to discover if the program behaves as expected

Sometimes there are things that we miss and things that the compiler misses

and the program crashes

We have to fix those problems

Often times a big part of developing an app

is trying to break it

trying to spot all the errors

but if everything goes well

the program finishes

So what are those things that the compiler checks?

One of them is the particular rules and

structure that Java has

Java pays particular attention to data

because programming is primarily about manipulating data

Java enforces a set of rules called the type system

to distinguish between different kinds of data

In Java each value must have a particular type

and by "type" I mean "category"

You can think about types as "categories"

For example, whole numbers or integers are of type "int"

They are a category that includes the number 4 or 2001

Another category is boolean

A boolean is something that can only have one of two values

A boolean is either true or false

Another example of a type

is String

A String is a sequence of characters

A String is a piece of text

"All your base", that's a String

How do we keep track of all this data?

We need to put the data somewhere

The place we put the data is a variable

Variables act as containers to hold the data

Just like the raw data, the container itself has a type

In a declaration, we specify

the variable's type as well as it's name

Here we have a variable

called "myValue"

with type "int", so we can put whole numbers into it

This is what we do with assignment

Here we are assigning the value 4 to the variable "myValue"

Note how the value 4 is an integer

the same type as its container

"myValue"

Declaration and assignment can also be combined

We see here two examples

In the first one we are putting the number 6 into "anotherValue"

In the second one, we are putting the characters

"War and Peace" into a variable called "longRead"

Variables aren't any good if we can't use them

to manipulate data

Here we are putting the value 16 into the variable "A"

Here we are putting the value 2 into the variable B

If we divide "A" by "B" we can put the result into in a variable called "C"

which will hold the value 8

The grey text you see on the right is called a comment

Anything that has two slashes in front of it

will be ignored by the compiler

It won't affect the running of the program

We will be using this notation throughout the slides

To give you another example

We have the value "Fish " which is being stored in the variable "main"

We've got the value "& Chips" being stored in the variable "side"

If we combine the two

we can store the result ("Fish & Chips") in the variable "meal"

"meal" will store the concatenated value "Fish & Chips"

To recap,

Java is an intermediary language used

to help communicate instructions to the computer

We use variables to store and manipulate data

Everything in Java must have a type

We declare variables by specifying the type as well as the name

We assign values to the variables with the '=' sign

Lastly, the type of data must match the type of the variable

Thanks for watching!

Join us for part 2, where we'll be

discussing objects, classes, and methods.