Basic Java Language - Revision history

wikademia>Wikademia: Text replace - '[[Topic:' to '[['

2009-06-08T03:53:31Z

Text replace - '[[Topic:' to '[['

← Older revision		Revision as of 03:53, 8 June 2009
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	}}		}}
	<br><br><hr>		<br><br><hr>
	<!--[[~~Topic:~~Java\|Back to Java Main Page]] \| [[Introduction_to_Java\|Previous Lesson]] \| [[Java_Decision_Structures\|Next Lesson]]-->		<!--[[Java\|Back to Java Main Page]] \| [[Introduction_to_Java\|Previous Lesson]] \| [[Java_Decision_Structures\|Next Lesson]]-->
	{{1lvlnav\|[[~~Topic:~~Java\|Java]]\|[[Introduction to Java]]\|[[Java Decision Structures]]}}		{{1lvlnav\|[[Java\|Java]]\|[[Introduction to Java]]\|[[Java Decision Structures]]}}

	[[Category:Java]]		[[Category:Java]]
	[[Category:Learning activities]]		[[Category:Learning activities]]
	[[Category:Basics]]		[[Category:Basics]]

wikademia>Wikademia at 20:58, 11 April 2009

2009-04-11T20:58:15Z

← Older revision		Revision as of 20:58, 11 April 2009
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	This lesson discusses the basics of the Java language, including variables, primitives, operators, statements and Java writing conventions.		This lesson discusses the basics of the Java language, including variables, primitives, operators, statements and Java writing conventions.
			{{ntnes}}
	== Touch on Classes ==		== 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.		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.

wikademia>Wikademia: 154 revisions

2009-04-10T20:02:54Z

154 revisions

← Older revision	Revision as of 20:02, 10 April 2009
(No difference)

60.54.23.251: /* Extends/Implements */

2008-12-17T01:47:45Z

Extends/Implements

← Older revision		Revision as of 01:47, 17 December 2008
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	===Extends/Implements===		===Extends/Implements===

	~~shit man~~		Extends/Implements not complete yet. Soon..

	== Statements ==		== Statements ==

60.54.23.251: /* Extends/Implements */

2008-12-17T01:47:00Z

Extends/Implements

← Older revision		Revision as of 01:47, 17 December 2008
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	===Extends/Implements===		===Extends/Implements===

	~~For the moment you can happily forget about this, it was included for completeness. For the object orientated experts, you will be pleased to know that this permits inheritance.~~		shit man




	== Statements ==		== Statements ==

wikademia>Lurkingfate: /* User Input */ Cleaned up code example.

2008-12-07T03:56:14Z

User Input: Cleaned up code example.

← Older revision		Revision as of 03:56, 7 December 2008
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	''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.''		''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.''

	<~~code~~>import javax.swing.JOptionPane;</~~code~~>		<source lang="java">import javax.swing.JOptionPane;</source>

	Now, let's go on to asking the user to enter a number and doing calculations on it. Basically: <source lang="java">JOptionPane.showInputDialog( null, "Hello, enter something" );</source>. Try putting that in a class (in the main method, of course) and run it. Currently, we can't do anything with it because the value is deleted.		Now, let's go on to asking the user to enter a number and doing calculations on it. Basically: <source lang="java">JOptionPane.showInputDialog( null, "Hello, enter something" );</source>. Try putting that in a class (in the main method, of course) and run it. Currently, we can't do anything with it because the value is deleted.

wikademia>Lurkingfate: /* Asking the user */ Changed section heading.

2008-12-07T03:55:23Z

Asking the user: Changed section heading.

← Older revision		Revision as of 03:55, 7 December 2008
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	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.		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.

	== ~~Asking the user~~ ==		== User Input ==

	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.		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.

wikademia>Lurkingfate: /* Subtraction '-', multiplication '', division '/', and modulus '%' operators / Cleaned up code examples.

2008-12-06T22:21:28Z

Subtraction '-', multiplication '*', division '/', and modulus '%' operators: Cleaned up code examples.

← Older revision		Revision as of 22:21, 6 December 2008
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	=== Subtraction '-', multiplication '*', division '/', and modulus '%' operators ===		=== Subtraction '-', multiplication '*', division '/', and modulus '%' operators ===
	Just like the addition operator, the subtraction, multiplication, division, and modulus operators are used as follows:		Just like the addition operator, the subtraction, multiplication, division, and modulus operators are used as follows:
	<~~pre~~>		<source lang="java">
	int a = 9;		int a = 9;

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	a*2; // evaluates to 18		a*2; // evaluates to 18
	a%4; // evaluates to 1		a%4; // evaluates to 1
	</~~pre~~>		</source>

	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.		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:		When more than one of the operators are used in the same statement, for example:
	<~~pre~~>		<source lang="java">
	int a, b, c, d;		int a, b, c, d;
	a = a-b/c*d;		a = a-b/c*d;
	</~~pre~~>		</source>

	the Java language would use the order-of-operations in this case.		the Java language would use the order-of-operations in this case.
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	Example:		Example:
	<~~pre~~>		<source lang="java">
	int a = 6; // assigns the value 6 to variable a		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		a += 5; // adds 5 to a, and assigns that value back into a, now a is 11
	</~~pre~~>		</source>

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

wikademia>Lurkingfate: /* Assignment Operators */ Cleaned up code examples.

2008-12-06T22:20:28Z

Assignment Operators: Cleaned up code examples.

← Older revision		Revision as of 22:20, 6 December 2008
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	The assignment operator, "=", sets the variable on its left equal to the value on its right. This code creates the variable ''a'' and sets it equal to 5		The assignment operator, "=", sets the variable on its left equal to the value on its right. This code creates the variable ''a'' and sets it equal to 5
	<~~pre~~>int a;		<source lang="java">int a;
	a = 5;</~~pre~~>		a = 5;
			</source>
	Fairly simple, right? Here is where it can get a slightly more tricky.		Fairly simple, right? Here is where it can get a slightly more tricky.

	<~~pre~~>int a;		<source lang="java">
			int a;
	int b;		int b;
	b = 6;		b = 6;
	a = b; //a equals 6</~~pre~~>		a = b; //a equals 6
			</source>

	At first glance, you might think that the last statement is setting ''a'' equal to the letter "b", but instead it is setting ''a'' equal to the ''value'' of ''b'', which is 6. Essentially, a holds the value of 6. You can also set a variable and declare it on the same line:		At first glance, you might think that the last statement is setting ''a'' equal to the letter "b", but instead it is setting ''a'' equal to the ''value'' of ''b'', which is 6. Essentially, a holds the value of 6. You can also set a variable and declare it on the same line:

	<~~pre~~>		<source lang="java">
	int a = 6;		int a = 6;
	</~~pre~~>		</source>

	However, you can't say <code>char myChar = y;</code> to set a character to 'y'. That would set the character variable <code>myChar</code> to the value stored in the character variable <code>y</code>. To set <code>myChar</code> equal to the character <i>y</i>, use a '''character literal''' — a technical term for "a character in single-quotes": <code>char myChar = 'y';</code>. Note that a <code>char</code> primitive can only hold a single character. <code>char myChar = 'Yo';</code> is illegal.		However, you can't say <code>char myChar = y;</code> to set a character to 'y'. That would set the character variable <code>myChar</code> to the value stored in the character variable <code>y</code>. To set <code>myChar</code> equal to the character <i>y</i>, use a '''character literal''' — a technical term for "a character in single-quotes": <code>char myChar = 'y';</code>. Note that a <code>char</code> primitive can only hold a single character. <code>char myChar = 'Yo';</code> is illegal.

wikademia>Lurkingfate: /* Asking the user */ Cleaned up code examples.

2008-12-06T18:17:39Z

Asking the user: Cleaned up code examples.

← Older revision		Revision as of 18:17, 6 December 2008
Line 355:		Line 355:

	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.		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.
	<~~pre~~>		<source lang="java">
	import java.util.Scanner;		import java.util.Scanner;
	Public class GettingStringInput		Public class GettingStringInput
Line 364:		Line 364:
	Scanner scan1 = new Scanner(System.in);		Scanner scan1 = new Scanner(System.in);
	System.out.print("Please enter a string: ");		System.out.print("Please enter a string: ");
	yourinput = scan1.nextLine()		yourinput = scan1.nextLine();
	}		}
	}		}
	</~~pre~~>		</source>

	''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.''		''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.''
Line 373:		Line 373:
	<code>import javax.swing.JOptionPane;</code>		<code>import javax.swing.JOptionPane;</code>

	Now, let's go on to asking the user to enter a number and doing calculations on it. Basically: <~~code~~>JOptionPane.showInputDialog( null, "Hello, enter something" )</~~code~~>. Try putting that in a class (in the main method, of course) and run it. Currently, we can't do anything with it because the value is deleted.		Now, let's go on to asking the user to enter a number and doing calculations on it. Basically: <source lang="java">JOptionPane.showInputDialog( null, "Hello, enter something" );</source>. Try putting that in a class (in the main method, of course) and run it. Currently, we can't do anything with it because the value is deleted.

	Because what you enter can consist of letters OR numbers, and any length of them, what is "produced" by that is a String. The following will work: <~~code~~>String mine = JOptionPane.showInputDialog( null, "Now I can set a String!" );</~~code~~>. Now lets say that after you get the string you want to print it. Just like regularly, add the following line: <~~code~~>System.out.println( mine );</~~code~~>.		Because what you enter can consist of letters OR numbers, and any length of them, what is "produced" by that is a String. The following will work: <source lang="java">String mine = JOptionPane.showInputDialog( null, "Now I can set a String!" );</source>. Now lets say that after you get the string you want to print it. Just like regularly, add the following line: <source lang="java">System.out.println( mine );</source>.

	Now you probably want to be able to enter a number. Java provides a method of changing a '''String''' to an <code>int</code>. It is <~~code~~>Integer.parseInt( String_Here );</~~code~~>. So lets say you want the user to enter a number and you print it. Do:		Now you probably want to be able to enter a number. Java provides a method of changing a '''String''' to an <code>int</code>. It is <source lang="java">Integer.parseInt( String_Here );</source>. So lets say you want the user to enter a number and you print it. Do:
	<~~pre~~>		<source lang="java">
	int mine = Integer.parseInt( JOptionPane.showInputDialog( null, "Now I can set an int!" ) );		int mine = Integer.parseInt( JOptionPane.showInputDialog( null, "Now I can set an int!" ) );
	System.out.println( mine );		System.out.println( mine );
	</~~pre~~>		</source>

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

Basic Java Language - Revision history

wikademia>Wikademia: Text replace - '[[Topic:' to '[['

wikademia>Wikademia at 20:58, 11 April 2009

wikademia>Wikademia: 154 revisions

60.54.23.251: /* Extends/Implements */

60.54.23.251: /* Extends/Implements */

wikademia>Lurkingfate: /* User Input */ Cleaned up code example.

wikademia>Lurkingfate: /* Asking the user */ Changed section heading.

wikademia>Lurkingfate: /* Subtraction '-', multiplication '*', division '/', and modulus '%' operators */ Cleaned up code examples.

wikademia>Lurkingfate: /* Assignment Operators */ Cleaned up code examples.

wikademia>Lurkingfate: /* Asking the user */ Cleaned up code examples.

wikademia>Lurkingfate: /* Subtraction '-', multiplication '', division '/', and modulus '%' operators / Cleaned up code examples.