Problems with local variable scope. How to solve it?

Question

I\'m getting the following error when trying to execute statemet.executeUpdate() in my code:

Local variable statement defined in an enclosing sc         


        

Answer 1

Firstly, we just CAN'T make the variable final as its state may be changing during the run of the program and our decisions within the inner class override may depend on its current state.

Secondly, good object-oriented programming practice suggests using only variables/constants that are vital to the class definition as class members. This means that if the variable we are referencing within the anonymous inner class override is just a utility variable, then it should not be listed amongst the class members.

But – as of Java 8 – we have a third option, described here :

https://docs.oracle.com/javase/tutorial/java/javaOO/localclasses.html

Starting in Java SE 8, if you declare the local class in a method, it can access the method's parameters.

So now we can simply put the code containing the new inner class & its method override into a private method whose parameters include the variable we call from inside the override. This static method is then called after the btnInsert declaration statement :-

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 Statement statement = null;                                 

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 Button btnInsert = new Button(shell, SWT.NONE);
 addMouseListener(Button btnInsert, Statement statement);    // Call new private method

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 private static void addMouseListener(Button btn, Statement st) // New private method giving access to statement 
 {
    btn.addMouseListener(new MouseAdapter() 
    {
      @Override
      public void mouseDown(MouseEvent e) 
      {
        String name = text.getText();
        String from = text_1.getText();
        String to = text_2.getText();
        String price = text_3.getText();
        String query = "INSERT INTO booking (name, fromst, tost,price) VALUES ('"+name+"', '"+from+"', '"+to+"', '"+price+"')";
        try 
        {
            st.executeUpdate(query);
        } 
        catch (SQLException e1) 
        {
            e1.printStackTrace();                                    // TODO Auto-generated catch block
        }
    }
  });
  return;
}

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