Basic Java Language: Difference between revisions

This lesson discusses the basics of the Java language, including variables, primitives, operators, statements and Java writing conventions.

== Touch on Classes ==

Everything in Java is written in classes. A Class in this context is a section of code that can contain data (variables), and instructions for processing that data (methods). Returning to the Hello World example from the [[Introduction to Java]], the class is defined on the first line, and everything within the curly brackets is within that class.

===Extends/Implements===

== Statements ==

== Operators ==

Operators are the symbols defining a certain operation to be performed.

=== Addition Operator '+' ===

=== Subtraction '-', multiplication '*', division '/', and modulus '%' operators ===

Just like the addition operator, the subtraction, multiplication, division, and modulus operators are used as follows:

int a = 9;

a*2; // evaluates to 18

a%4; // evaluates to 1

Subtraction, multiplication, and division, you have seen before, but the modulus operator is much less commonly used. Actually, it is commonly used, but it known under a different name, the remainder. Nine divided by four gives a remainder of one, so therefore 9%4 (pronounced "9 mod 4") evaluates to 1.

When more than one of the operators are used in the same statement, for example:

int a, b, c, d;

a = a-b/c*d;

the Java language would use the order-of-operations in this case.

Example:

int a = 6; // assigns the value 6 to variable a

a += 5; // adds 5 to a, and assigns that value back into a, now a is 11

==== Minus-equals, multiply-equals, divide-equals, and mod-equals ====

Identifiers should also be meaningful, while maintaining practicality. If calculating the sum of a set of numbers, <code>sum<code> is better than <code>cumulativeTotal</code>, but <code>s</code> might be too short.

You can also print out multiple variables on the same line:

Note that this won't work for two literal numeric values:

Now you can do calculations and print the result! For example, say you want to print 6*6*6*6. Here is the code:

public class Multiplying

{

   }

}

== Compiling and running your program ==

If, when running, it reports "invalid class file", the compiler might not have created a file. It should have given an error message at compile time.

The first way to get user input is from the keyboard without using the swing gui. You must first import the Scanner package first like so. <code>import java.util.Scanner;</code> Once you have done that you will have to create a Scanner object. <code>Scanner scan1 = new Scanner(System.in);</code> Finally after the user has entered the input asked for you retrieve using your Scanner object. For example if we wanted a string as input we could use the following code.  

import java.util.Scanner;

Public class GettingStringInput

       Scanner scan1 = new Scanner(System.in);

       System.out.print("Please enter a string: ");

   }

}

''In order for the following to work properly, you must place the following code on the first line of your .java file. Importing packages will be explained later.''

int mine = Integer.parseInt( JOptionPane.showInputDialog( null, "Now I can set an int!" ) );

System.out.println( mine );

And now, of course, you can do whatever you want with that...

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[[Category:Java]]

[[Category:Learning activities]]

[[Category:Basics]]