Freelancer Hridoy :: Programmer, Youtuber, Android App Developer & Social Entrepreneur: Variables and Data Types in Java Programming

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<b><span style="color: blue;"><a href="https://www.youtube.com/watch?v=IXkDSMAhdk0&list=PLoVO9Yha8Fi1BjDWHeKnhsMWNHt44ICrH" target="_blank">👉Variables and Data Types in Java Programming</a></span></b></h2>
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<b>Variables </b>are locations in memory in which values can be
stored. They have a name, a type, and a value. Before you can use a variable,
you have to declare it. After it is declared, you can then assign values to it.<o:p></o:p></div>
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Java
actually has three kinds of variables: instance variables, class variables, and
local variables.<o:p></o:p></div>
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Instance variables, as you learned yesterday, are used to
define attributes or the state for a particular object. Class variables are
similar to instance variables, except their values apply to all that class’s
instances (and to the class itself) rather than having different values for
each object.<o:p></o:p></div>
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Local variables are declared and
used inside method definitions, for example, for index counters in loops, as
temporary variables, or to hold values that you need only inside the method
definition itself. They can also be used inside blocks ({}), which you’ll learn
about later this week. Once the method (or block) finishes executing, the
variable definition and its value cease to exist. Use local variables to store
information needed by a single method and instance variables to store
information needed by multiple methods in the object.<o:p></o:p></div>
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Although all three kinds of variables are declared
in much the same ways, class and instance variables are accessed and assigned
in slightly different ways from local variables. Today, you’ll focus on
variables as used within method definitions; tomorrow, you’ll learn how to deal
with instance and class variables.<o:p></o:p></div>
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                                                👇</div>
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👉<b><span style="color: blue;"><a href="https://www.youtube.com/watch?v=IXkDSMAhdk0&list=PLoVO9Yha8Fi1BjDWHeKnhsMWNHt44ICrH" target="_blank">See More Videos About Java Programming Click Here</a></span></b></div>
<h4>
Declaring Variables<o:p></o:p></h4>
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To use any variable in a Java
program, you must first declare it. Variable declarations consist of a type and
a variable name:<o:p></o:p></div>
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<span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 102%;"><b>int myAge; String myName; boolean isTired;</b></span></h2>
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Variable definitions can go
anywhere in a method definition (that is, anywhere a regular Java statement can
go), although they are most commonly declared at the beginning of the
definition before they are used:<br />
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<span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 102%;"><b>public static void main (String args</b></span><b><span style="font-family: "segoe ui symbol" , "sans-serif"; font-size: 7.5pt; line-height: 102%;">÷</span><span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 102%;">])  
{</span><o:p></o:p></b><b><span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 102%;">    int count;     String title;     boolean isAsleep;</span></b><span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 102%;"><b>... }</b></span></h2>
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You can string together variable
names with the same type:<o:p></o:p></div>
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<span style="font-family: "times new roman" , serif; font-size: 7.5pt; line-height: 102%;">int x, y, z; String firstName, LastName;</span></h2>
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You can also give each variable
an initial value when you declare it:<o:p></o:p></div>
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<span style="font-family: "times new roman" , serif; font-size: 7.5pt; line-height: 102%;">int myAge, mySize, numShoes = 28; String myName = “Laura”;
boolean isTired = true; int a = 4, b = 5, c = 6;</span></h2>
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<o:p></o:p></div>
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If there are multiple variables
on the same line with only one initializer (as in the first of the previous
examples), the initial value applies to only the last variable in a
declaration. You can also group individual variables and initializers on the
same line using commas, as with the last example, above.<o:p></o:p></div>
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Local variables must be given values before they can be
used (your Java program will not compile if you try to use an unassigned local
variable). For this reason, it’s a good idea always to give local variables
initial values. Instance and class variable definitions do not have this
restriction (their initial value depends on the type of the variable: <span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 100%;">null</span>
for instances of classes, <span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 100%;">0</span> for numeric variables, <span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 100%;">‘\0’</span> for characters, and <span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 100%;">false</span>
for booleans).<o:p></o:p></div>
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Notes on Variable Names</h2>
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<o:p></o:p></h4>
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Variable names in Java can start
with a letter, an underscore (<span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 100%;">_</span>), or a dollar sign (<span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 100%;">$</span>) . They cannot start with a
number. After the first character, your variable names can include any letter
or number. Symbols, such as <span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 100%;">%</span>, <span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 100%;">*</span>, <span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 100%;">@</span>, and so on, are often reserved for operators in
Java, so be careful when using symbols in variable names.<o:p></o:p></div>
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<b>Caution: </b>The Unicode specification is a two-volume set of lists
  of thousands of characters. If you don’t understand Unicode, or don’t think
  you have a use for it, it’s safest just to use plain numbers and letters in
  your variable names. You’ll learn a little more about Unicode later on.<o:p></o:p></div>
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<span style="font-family: "garamond" , serif; font-size: 10.5pt;">In addition, the Java language uses the Unicode
character set. Unicode is a character set definition that not only offers
characters in the standard ASCII character set, but also several million other
characters for representing most international alphabets. This means that you </span>can use accented characters and other glyphs as legal
characters in variable names, as long as they have a Unicode character number
above <span style="font-family: "times new roman" , serif; font-size: 7.5pt; line-height: 100%;">00C0</span>.</div>
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Finally,
note that the Java language is case-sensitive, which means that uppercase
letters are different from lowercase letters. This means that the variable <span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 100%;">X</span>
is different from the variable <span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 100%;">x</span>, and a <span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 100%;">rose</span> is not a <span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 100%;">Rose</span> is not a <span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 100%;">ROSE</span>.
Keep this in mind as you write your own Java programs and as you read Java code
other people have written.<o:p></o:p></div>
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By convention, Java variables have meaningful names, often
made up of several words combined. The first word is lowercase, but all
following words have an initial uppercase letter:<o:p></o:p></div>
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<span style="font-family: "times new roman" , "serif"; font-size: 7.5pt; line-height: 102%;">Button theButton; long reallyBigNumber; boolean
currentWeatherStateOfPlanetXShortVersion;</span>
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Variable Types</h2>
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In addition to the variable name, each variable declaration
must have a type, which defines what values that variable can hold. The
variable type can be one of three things:<o:p></o:p></div>
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<span style="font-family: "segoe ui symbol" , "sans-serif"; mso-bidi-font-family: "Segoe UI Symbol"; mso-fareast-font-family: "Segoe UI Symbol";">■
</span>One of the eight basic primitive data types<o:p></o:p></div>
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<span style="font-family: "segoe ui symbol" , "sans-serif"; mso-bidi-font-family: "Segoe UI Symbol"; mso-fareast-font-family: "Segoe UI Symbol";">■
</span>The name of a class<o:p></o:p></div>
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<span style="font-family: "segoe ui symbol" , "sans-serif"; mso-bidi-font-family: "Segoe UI Symbol"; mso-fareast-font-family: "Segoe UI Symbol";">■
</span>An array<o:p></o:p></div>
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You’ll learn about how to declare and use array variables in
Chapter 5.<o:p></o:p></div>
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The eight primitive data types
handle common types for integers, floating-point numbers, characters, and
boolean values (true or false). They’re called primitive because they’re built
into the system and are not actual objects, which makes them more efficient to
use. Note that these data types are machine-independent, which means that you
can rely on their sizes and characteristics to be consistent across your Java
programs.<o:p></o:p></div>
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There are four Java integer
types, each with different ranges of values (as listed in Table 3.1). All are
signed, which means they can hold either positive or negative numbers. Which
type you choose for your variables depends on the range of values you expect
that variable to hold; if a value becomes too big for the variable type, it is
truncated.<o:p></o:p></div>
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👉Variables and Data Types in Java Programming Variables are locations in memory in which values can be stored. They have a nam...

Freelancer Hridoy :: Programmer, Youtuber, Android App Developer & Social Entrepreneur

Freelancer Hridoy :: Programmer, Youtuber, Android App Developer & Social Entrepreneur

Monday, August 20, 2018

Variables and Data Types in Java Programming

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