Java - Revision history

Hdridder at 18:52, 28 June 2022

2022-06-28T18:52:15Z

← Older revision		Revision as of 18:52, 28 June 2022
Line 19:		Line 19:
	;private int var1;		;private int var1;
	:Private variables in classes can only be accessed from within the class (same for methods).		:Private variables in classes can only be accessed from within the class (same for methods).

			=Access levels=
			* Public all can use it. Public attributes can be changes by all
			* Protected, can be used within the class, by subclasses and by classes in the same package (A package is a group of related classes in one namespace)
			* Default, like protected but no access from subclasses outside the package. If nothing is specified it is Default.
			* Private can only be used within the class

	=Methods=		=Methods=

Hdridder at 12:34, 17 June 2022

2022-06-17T12:34:10Z

← Older revision		Revision as of 12:34, 17 June 2022
Line 24:		Line 24:
	* A 'void' method is a method with no return value, else the return value type must be specified		* A 'void' method is a method with no return value, else the return value type must be specified
	* Private methods in classes can only be accessed from within the class (same for variables).		* Private methods in classes can only be accessed from within the class (same for variables).

			=Classes=
			abstract classes cannot be instantiated by itself it is only a superclass for its subclasses.

			;public class <subclass> extends <superclass>
			:Instantiate a subclass object

			<syntaxhighlight lang=java>
			public class <subclass> extends <superclass> {
			public <subclass> (<types and attributes from superclass>)
			super(<attributes defined in superclass>)
			}
			private <type> <subclass specific attribute>

			public void <subclass specific method>() {
			}
			</syntaxhighlight>

			Superclasses can have 'protected' attributes and methods making them available for subclasses and in the same package.

			Methods and attributes in subclasses can override the superclass methods and attributes.

			=Interfaces=
			A bit like subclasses but only describing the methods used from the superclass. It does not implement the method but only declares it. The implementation is in the subclass. A subclass can implement multiple interfaces unlike inheritance that can have only 1 superclass.

			Interface can extend other interfaces.

			<syntaxhighlight lang=java>
			public class <subclass> implements <interface> {
			<attribute declarations>

			public void <method from interface>() {
			}
			}
			</syntaxhighlight>

Hdridder at 09:04, 17 June 2022

2022-06-17T09:04:02Z

← Older revision		Revision as of 09:04, 17 June 2022
Line 1:		Line 1:
	20220531		20220531

	Fist notes on java ~~progamming~~.		Fist notes on java programming.

	<syntaxhighlight lang=java>		<syntaxhighlight lang=java>
Line 15:		Line 15:
	=Variables=		=Variables=
	;int var1 = 0		;int var1 = 0
	:Variables must be declared and ~~initialised~~		:Variables must be declared and initialized

			;private int var1;
			:Private variables in classes can only be accessed from within the class (same for methods).

			=Methods=
			* Every program must have a main method, that is executed when the program starts
			* A 'void' method is a method with no return value, else the return value type must be specified
			* Private methods in classes can only be accessed from within the class (same for variables).

Hdridder: Created page with "20220531 Fist notes on java progamming. public class HelloWorld { public static void main(String args[] ) { String text = "hello world"; Sys..."

2022-05-31T19:41:20Z

Created page with "20220531 Fist notes on java progamming. <syntaxhighlight lang=java> public class HelloWorld { public static void main(String args[] ) { String text = "hello world"; Sys..."

New page

20220531

Fist notes on java progamming.

<syntaxhighlight lang=java>
public class HelloWorld {
public static void main(String args[] ) {
String text = "hello world";
System.out.println( text );
}
}
</syntaxhighlight>
If a class implements an interface all methods in that interface must be defined in the class

=Variables=
;int var1 = 0
:Variables must be declared and initialised