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Inner
Classes
Inner
classes let you define one class within another.
They provide a type of scoping for your classes
since you can make one class a member of another
class.
Just as classes have member variables and methods,
a class can also have member classes.
| class
Outer { |
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/class Inner { } |
| }//
End of class |
if you compile it,
%javac Outer.java
you’ll
end up with two class files:
Outer.class
Outer$Inner.class
e.g.
| class
Outer { |
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private int x = 5;
public void outerMethod() {
Inner in = new Inner();
in.innerMethod();
}
class Inner {
public void innerMethod() {
System.out.println("Outer variable
x is " + x);
}
} |
| }//
End of class |
| You
can create four different types of inner
classes, based upon the how and the where
of creation. |
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Nested top-level classes
If you declare a class within a class and
specify the static modifier, the compiler
treats the class just like any other top-level
class. Any class outside the declaring class
accesses the nested class with the declaring
class name acting similarly to a package.
eg, outer.inner. Top-level inner classes
implicitly have access only to static variables.
There can also be inner interfaces. All
of these are of the nested top-level variety.
Member classes
Member inner classes are just like other
member methods and member variables and
access to the member class is restricted,
just like methods and variables. This means
a public member class acts similarly to
a nested top-level class. The primary difference
between member classes and nested top-level
classes is that member classes have access
to the specific instance of the enclosing
class.
Local classes
Local classes are like local variables,
specific to a block of code.Their visibility
is only within the block of their declaration.
In order for the class to be useful beyond
the declaration block, it would need to
implement a more publicly available interface.Because
local classes are not members, the modifiers
public, protected, private, and static are
not usable.
Anonymous classes
Anonymous inner classes extend local inner
classes one level further. As anonymous
classes have no name, you cannot provide
a constructor. |
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[
Received from Seeny Desai ]
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