Wednesday, July 15, 2015

Inner Classes-2(Local Classes)

         In java you could define a class inside a code block/Method. This kind of classes are known as Local classes .       Lets look at an Example :
public class HelloWorld{
    public int studentId;
 public  void method(){
    int loop=0;
    final int CONSTANT=10;
    System.out.println("Main Execution begins , Student id is :" +studentId);
    class  LocalClass{
     public void printStudentId(){
      System.out.println("Inside Inner class, Student id is :" +studentId); // Remember that if studentId is also present in local class
                                                                         // this will print the local class variable student id , in such cases  use Student.this.studentId
            System.out.println("Inside Inner class, CONSTANT is :" +CONSTANT); // only final local variables can be accessed.
             System.out.println("Inside Inner class, loop is :" +loop); // errors out , loop is not final
   LocalClass local = new LocalClass();
   public static void main(String args[]){
       HelloWorld hello = new HelloWorld();

Some points to remember:
 1. A local class can access variables inside outer class (instance variables of outer class)
 2. A local class cannot be instatiated/visible outside the code block/method.
 3. A local class cannot access non final local variables as they both have different scopes , Local variables get destroyed on method exit . But final local variables are accessible inside local classes. Final variables are copied to the code stack internally before the inner class instance is created and can be used inside.

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