Recitation 2: Variables, Initialization, Assignment, Declaration, Boolean Expressions, installing and running java programs
Recitation 2 What are variables? What is declaration, assignment, initialization, a boolean expression, types, and syntax?
A variable is a piece of memory that can contain a data value.
A declaration is writing out the type and variable name.
<type> <var name>; ex.
An initialization is assigning a value to a variable
<var name> = <value>; ex.
x = 5;
An assignment is the whole thing, meaning you do both.
<type> <varname> = <value>; ex.
int x = 5;
In programming languages every variable has a type. In java there are two categories: primitives and reference. Let’s focus on primitives for now. They are:
- • int – ex. 1,5,-800
- • float – ex. 5.0
- • double – ex. 6.0
- • char – ex. ‘a’,’@’,’!’,’Z’
- • boolean – ex. true, false
Boolean expressions evaluate to true or false. They use operators like
!. You can find these expressions in the conditional part of if statements. Boolean expression can be found in the parenthesis of
while(<Boolean Expression>), and
How to install Java, compile and run java code
The extended post is here, which describes what exactly the JDK and all of this is, but here are the steps and basics.
1) Download the JDK (java so you can code in it and run your programs) for your operating system.
2) Run the installer (whatever.EXE for windows, something.dmg for OSX, or run a command this command for linux
sudo dpkg -i /path/to/deb/file followed by sudo apt-get install -f)
3) Open up CMD/Powershell (windows) or Terminal (OSX, Linux)
4) Type in the command
javaand you should see a bunch of text.
java -versionwill also let you know if you have it installed and will obviously output the version.
5) Type in the command
javacand you should see some documentation like
Usage: javac <options> <source files> where possible options include:. Now if you are on windows and don’t see it you should update your system path variable to include the bin folder. Here is a link or too on how to do that. If you have a MAC here is how to set the path variable.
6) Now the commands you need to know are
cd ..to go up a directory),
pwd(tells you where you are in your file system),
javac <FileName.java>- to compile,
java <FileName>- to run. Technically your filename is the same as your class name as we will learn later in the semester.
Post originally posted on 2018-01-28 20:00:00 -0500
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