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  • Welcome to Java Fundamentals for Android: Part 1

  • 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.

Welcome to Java Fundamentals for Android: Part 1

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