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javainterface
Bartholomew Surma
Bartholomew Surma

Reputation: 53

Java: why Observer is NOT an interface

import java.util.*;
import java.awt.*;
import java.awt.event.*;
import java.applet.Applet;

class Client extends Button implements Observer, ActionListener{
...
}

with the code above, when i try to compile it with jdk (v 1.7.0_17) i get the following error:

error: interface expected here
class Client extends Button implements Observer, ActionListener{
                                       ^

while on other computers it works (I've only checked it on 2 different linuxes) just fine. I'm using Windows 7 Professional 64-bit.

Upvotes: 3

Views: 370

Answers (1)

Jon Skeet
Jon Skeet

Reputation: 1500075

java.util.Observer most definitely is an interface.

I suspect you've got an Observer class within the same package as Client, which would certainly cause that problem.

Complete examples:

This compiles fine:

import java.util.*;
import java.awt.*;
import java.awt.event.*;

class Client extends Button implements Observer, ActionListener {
    public void update(Observable x, Object y) {}
    public void actionPerformed(ActionEvent event) {}
}

This doesn't:

import java.util.*;
import java.awt.*;
import java.awt.event.*;

class Observer {} // Awooga! Awooga!

class Client extends Button implements Observer, ActionListener {
    public void update(Observable x, Object y) {}
    public void actionPerformed(ActionEvent event) {}
}

Upvotes: 6

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