Object Orientation - Revision history

Suhridk: /* Protected */

2011-09-13T12:34:18Z

Protected

2011-09-12T14:31:08Z

Protected

2011-09-12T14:20:13Z

Protected

2011-09-08T07:47:23Z

Static Members =

2011-09-06T13:27:34Z

Overriding

2011-09-06T07:58:53Z

Protected

2011-09-06T07:57:19Z

Protected

2011-09-05T05:23:11Z

Casting

2011-09-04T07:22:19Z

Protected

2011-08-25T13:10:33Z

@@ Line 160: / Line 160: @@
+}
-</syntaxhighlight>
+=== protected static methods and constructors ===
 <u> Abstract Methods </u>

@@ Line 29: / Line 29: @@
 * For subclasses in other packages, protected members (both fields and methods) are '''only accessible through inheritance''' in the subclass.
 * The subclass in a different package cannot use a super-class reference to access the protected member.
 * The keyword '''super''' can be used to access the protected member from within a subclass.
@@ Line 141: / Line 142: @@
 		Dog d = new Dog();
 		d.dawg();
+	}

@@ Line 300: / Line 300: @@
 </syntaxhighlight>
-=== Static Members ====
+=== Static Members ===
 * When it comes to statics, subclasses can redefine static memebers (variables and methods). They are not overrides.
@@ Line 351: / Line 351: @@
 		System.out.println(s.move()); //Ship Move
+	}
+}

@@ Line 295: / Line 295: @@
 	public void handleMe() throws UnknownHostException  { //NOT OK, newer checked exception being declared
 		System.out.println("Handler.handleMe()");
+	}
+}

@@ Line 28: / Line 28: @@
 * For classes and subclasses in the same package protected works in exactly the same way as package(default).
 * For subclasses in other packages, protected members (both fields and methods) are '''only accessible through inheritance''' in the subclass.
 * The subclass in a different package cannot use a super-class reference to access the protected member.
 <syntaxhighlight lang="java5">

← Older revision		Revision as of 05:23, 5 September 2011
Line 360:		Line 360:
	OutOfMemoryError ome = (OutOfMemoryError) oie; //An Exception can never be an Error		OutOfMemoryError ome = (OutOfMemoryError) oie; //An Exception can never be an Error

		+
		+	</syntaxhighlight>
		+
		+	* The cast need not be of the same type as that of the reference variable, it can be of a sub-type as well:
		+
		+	<syntaxhighlight lang="java5">
		+
		+	interface Computable {
		+	}
		+
		+	class Electronics {
		+	}
		+
		+	class Computer extends Electronics implements Computable {
		+	}
		+
		+	class Laptop extends Computer {
		+	}
		+
		+	public class Casting {
		+
		+	public static void main(String[] args) {
		+
		+	Electronics e = new Laptop();
		+
		+	Electronics e2 = (Computer) e;
		+
		+	Computer comp = (Laptop) e;
		+
		+	}
		+	}

	</syntaxhighlight>		</syntaxhighlight>

@@ Line 27: / Line 27: @@
 * Protected is '''wider''' than package. Protected = package + subclasses.
 * For classes and subclasses in the same package protected works in exactly the same way as package(default).
-* For subclasses in other packages, protected members (both fields and methods) are only accessible through inheritance in the subclass.
+* For subclasses in other packages, protected members (both fields and methods) are '''only accessible through inheritance''' in the subclass.
 * The subclass in a different package cannot use a reference to super to access the protected member.

← Older revision		Revision as of 13:10, 25 August 2011
Line 340:		Line 340:

	}		}
		+
		+	</syntaxhighlight>
		+
		+	== Casting ==
		+
		+	* References can be cast if the types belong in the same hierarchy.
		+	* This means that an Object reference can be cast to anything.... because everything is an Object.
		+	* However, the compiler can figure out if two references are of completely different types and they cannot be cast
		+
		+	<syntaxhighlight lang="java5">
		+
		+	Object obj = new String();
		+	String str = (String) obj; //OK, an object can be a String.
		+
		+	Object obj2 = new Integer();
		+	String str2 = (String) obj2; //Compiler says OK - but this will fail at runtime with a ClassCastException
		+
		+	Exception oie = new InterruptedException();
		+	OutOfMemoryError ome = (OutOfMemoryError) oie; //An Exception can never be an Error
		+

	</syntaxhighlight>		</syntaxhighlight>