Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <blockquote> <p>My question is, why isn't ClassB's method being used?</p> </blockquote> <p>Not true. The method used is <code>ClassB</code>'s method, which it inherited from <code>ClassA</code>.</p> <hr> <p>I think the main reason behind the confusion here is the fact that the method actually is not <strong>overridden</strong>, instead it is <strong>overloaded</strong>. Although <code>Integer</code> is a subtype of <code>Number</code>, since <em>method parameter is invariant</em> in Java, the method <code>public void method(Integer d)</code> doesn't override the method <code>public void method(Number n)</code>. So, <code>ClassB</code> ends up having two (overloaded) methods.</p> <p>Static binding is used for overloaded methods, and the method with most specific parameter type is chosen by the compiler. But in this case, why does the compiler pick <code>public void method(Number n)</code> instead of <code>public void method(Integer d)</code>. That's because of the fact that the reference that you are using to invoke the method is of type <code>ClassA</code>. </p> <pre><code>ClassA a = new ClassB(); //instance is of ClassB (runtime info) a.method(3); //but the reference of type ClassA (compiletime info) </code></pre> <p>The only method that <code>ClassA</code> has is <code>public void method(Number n)</code>, so that's what the compiler picks up. Remember, here the expected argument type is <code>Number</code>, but the actual argument, the integer 3, passed is auto-boxed to the type <code>Integer</code>. And the reason that it works is because the <em>method argument is covariant</em> in Java. </p> <p>Now, I think it's clear why it prints</p> <blockquote> <p>ClassA: 3 class java.lang.Integer</p> </blockquote>
    singulars
    1. This table or related slice is empty.
    1. POUsing inherited overloaded methods
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USBhesh Gurung
    1. USBhesh Gurung
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POUsing inherited overloaded methods
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTAcceptedByOriginator
    1. COI feel like this might be the reason, could you expand a little on your last paragraph?
      singulars
      1. PO
      1. USFede Rico
    2. CO@FedeRico: I updated it, hope it helps you understand what's going on.
      singulars
      1. PO
      1. USBhesh Gurung
    3. COI think that this answer (so far) has been the clearest as to what is going on. The key here is that the binding for a method invocation is resolved during *compilation* and is dependent upon the *declared type* of the variable. The *declared type* is `ClassA` and therefore the method ClassB#method(Integer) is unavailable for selection. See http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.12.1 - under the bullet point "In all other cases, the qualified name has the form FieldName . Identifier."
      singulars
      1. PO
      1. USlifelongcoug
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload