Wednesday, August 20, 2008

Java Access specifiers

Hi,
in java there is one more interesting concept about access specifiers
the following four access speciers are there in java
private
default (no access specifier keep blank)
protected
public
Now the explanation as below with example
Private
the private access specifier for only with in the class accessible not other than class
example
public class Person
{
private String name;
}
class Employee extends Person
{
public String helloString()
{
return name; // here it will show compilation error Person.name is not visible because
private access specifier used in Person class for name
}

}
public
we used this specifier variables, methods any where in any class
in other packages also we can use this variables and methods
example
package com.test;
public class Person
{
public String name = "siva";
}
package com.test1;
import com.test.Person;
public class Person extends Person
{
public String helloString()
{
return name;
}
}
if we take this scenario it will work fine here one more concept you need to know
Person class is extending Person class only why it is not showing exception
Because one Person class in one package
another Person class in another package
so public access specifier you can use any package any class you need to extend that classes
accordingly.
default(if you are not specifing any access specier it is default)
this access is package level access
example
package com.test
public Class Person
{
String name = "siva";
public static void main(String args[])
{
Employee e = new Employee()
System.out.println("Name is "+e.getPersonDetails());
}
}
class Employee extends Person
{
public String getPersonDetails()
{
return name;
}
}
in this Example you need not identify one more concept.
in one package two classes are there but one class having public one is having nothing
in any package accepts only one public class

protected
one of most important concept for interviews
suppose we have two packages
1 com.test;
2 com.test1;
package com.test; having one class with protected method
package com.test1;
two class one class not overriding protected method directly using that method.
now the second class in com.test1 package is extending the same package class
the protected method is available only for first class of in second package i.e com.test1
not for second class
if you are try to access that method it will through exception.
the good example is Object class Clone method it is protected

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