Inner Classes - Revision history

Suhridk: /* Introduction */

2011-08-10T08:11:15Z

Introduction

2011-08-10T08:10:52Z

Introduction

2011-08-10T08:09:45Z

Local Inner Classes

2011-08-10T08:09:18Z

Regular inner classes

2011-08-10T07:37:46Z

Anonymous Inner Classes

2011-08-10T07:33:13Z

Anonymous Inner Classes

2011-08-10T07:31:30Z

Anonymous Inner Classes

2011-08-10T07:30:28Z

Anonymous Inner Classes

2011-08-10T07:27:02Z

Anonymous Inner Classes

2011-08-10T07:10:45Z

Anonymous Inner Classes

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 * Think of the inner class as sort of a MEMBER of the outer class.
 * So access modifiers can be used (public, private etc) for inner class declarations.
-* In general inner classes cannot have static members (variables and methods) except for static inner classes.
+* '''In general inner classes cannot have static members (variables and methods) except for static inner classes.'''
 == Regular inner classes ==

@@ Line 5: / Line 5: @@
 * Think of the inner class as sort of a MEMBER of the outer class.
 * So access modifiers can be used (public, private etc) for inner class declarations.
 == Regular inner classes ==

@@ Line 133: / Line 133: @@
 * Block could mean - method body, local block, static initializer, instance initializer.
 * Local class is treated like a method local variable - it can not be marked as public, private, protected, static, transient.
-* Local classes CANNOT have static members - variables or methods.
+* Local classes '''CANNOT have static members''' - variables or methods.
 * Scope - its scope is limited to the block.
 * Class can ONLY be instantiated from within the method where it is declared. That too, after the class definition. Not anywhere else.

@@ Line 10: / Line 10: @@
 * A regular class is defined as a member of the outer class. (analogous to a non-static field).
 * An inner class is ''tied to an outer-class instance'' - so it can access instance specific information.
-* This implies that  regular Inner classes '''cannot have any statics''' (variables or methods)
+* This implies that  regular Inner classes '''cannot have any statics''' (variables or methods) Exception is it can have final static variables (essentially constants).
 * Only way to access an instance of the inner classes is through an instance of the outer class.
 * Remember the funny syntax:

← Older revision		Revision as of 07:37, 10 August 2011
Line 282:		Line 282:
	<syntaxhighlight lang="java5">		<syntaxhighlight lang="java5">

		+	class A {
		+
		+	private String s;
		+
		+	A(String s) {
		+	this.s = s;
		+	}
		+
		+	void foo() {
		+	System.out.println("foo()");
		+	}
		+
		+	String getS() {
		+	return s;
		+	}
		+	}
		+
		+	public class Anon2 {
		+
		+	public static void main(String[] args) {
		+	A a1 = new A("Hello") { //Passing the arguement to anon class's super constructor
		+	@Override
		+	void foo() {
		+	System.out.println("foo() " + getS());
		+	}
		+	};
		+
		+	a1.foo(); //prints "foo() Hello"
		+	}
		+
		+	}

@@ Line 275: / Line 275: @@
                  //Anonymously extending the same class while overriding a method. This will print "override"
+}
 </syntaxhighlight>

@@ Line 175: / Line 175: @@
 * Perhaps the most popular of the inner classes. Used to extend classes or implement interfaces. Convenient for defining classes on the spot. Used a lot in Swing, Threads.
 * Since anonymous class is actually always a subclass - only methods that are in the reference type can be called.
-* It is anonymous - because a new type is not declared using the class keyword.
+* It is anonymous - because a new type is not declared using the class keyword and the classes do not have a name. An instance can be created ''only'' alongwith class definition.
 * Similar to local classes - '''no static keywords permitted anywhere.'''
 * See example below. We need to create a new thread just in a method. Instead of defining a separate thread class, implementing runnable etc. We can do the following:

@@ Line 172: / Line 172: @@
 == Anonymous Inner Classes ==
-* Perhaps the most popular of the inner classes.
+* Anonymous classes combine the process of class definition and instantiation.
-* Used to extend classes or implement interfaces.
+* Perhaps the most popular of the inner classes. Used to extend classes or implement interfaces. Convenient for defining classes on the spot. Used a lot in Swing, Threads.
-* Since anonymous class is actually always a subclass - only methods that are in the reference type can be called. See below.
+* Since anonymous class is actually always a subclass - only methods that are in the reference type can be called.
 * It is anonymous - because a new type is not declared using the class keyword.
-* Convenient for defining classes on the spot. Used a lot in Swing, Threads.
+* Similar to local classes - no static members permitted.
 * See example below. We need to create a new thread just in a method. Instead of defining a separate thread class, implementing runnable etc. We can do the following:

@@ Line 274: / Line 274: @@
 		}.anon());
                  //Anonymously extending the same class while overriding a method. This will print "override"
+}