What is the Final Keyword in Java? How to use Final Keyword – Java Tutorial
Solution:
The final keyword can be applied in three places in Java Program,
–>For declaring variables
–>For declaring the methods
–>For declaring the class
Video Tutorial – Final Keyword
The Final Keyword for variables
A variable can be declared as final.
If a particular variable is declared as final then it cannot be modified further.
The final variable is always a constant.
For example – final int a = 10;
The Final Keyword for variable – Example Program
class Test
{
final int a =10;
void fun()
{
System.out.println("\n Hello, this function declared using final");
}
}
class Test1 extends Test
{
int a = 20;
}
class finaldemo
{
public static void main(String args[])
{
Test t = new Test1();
t.fun();
}
}
Output:
1 Error
Cannot override final variable a in-class Test1
The Final Keyword for Method
The final keyword can also be applied to the method. When a final keyword is applied to the method, the method overriding is avoided.
That means the methods that are declared with the keyword final cannot be overridden.
Consider the following Java program which makes use of the keyword final for declaring the method –
The Final Keyword for Method – Example
class Test
{
final void fun()
{
System.out.println("\n Hello, this function declared using final");
}
}
class Test1 extends Test
{
final void fun()
{
System.out.println("\n Hello, this another function");
}
}
class finaldemo
{
public static void main(String args[])
{
Test t = new Test1();
t.fun();
}
}
Output:
1 Error
fun() in Test1 cannot override fun() in Test; overridden method is final final void fun()
The Final Keyword for Class declaration
If we declare a particular class as final, no class can be derived from it.
Following the Java program is an example of final classes.
The Final Keyword for Class declaration – Example
final class Test
{
void fun()
{
System.out.println("\n Hello, this function in base class");
}
}
class Test1 extends Test
{
final void fun()
{
System.out.println("\n Hello, this another function");
}
}
class finalclassdemo
{
public static void main(String args[])
{
Test t = new Test1();
t.fun();
}
}
Output:
1 Error
cannot inherit from final Test class Test1 extends Test
Summary:
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