super（）不在子类'构造函数中工作

Question

Superclass:

public class CwDB{
protected LinkedList<Entry> dict = null;

public CwDB(String filename){
        this.dict = new LinkedList<Entry>();
        try{
            FileReader fr = new FileReader(filename);
            BufferedReader br = new BufferedReader(fr);
            String w = null;
            while((w = br.readLine()) != null ){
                String c = br.readLine();
                this.add(w,c); //adds new Entry to dict
            }
            br.close();
            fr.close();
        }catch(IOException e){
            e.printStackTrace();
        }
}
public void add(String word, String clue){
    this.dict.add(new Entry(word,clue));
}
...
}

Subclass:

public class InteliCwDB extends CwDB {

public InteliCwDB(String filename){
    super(filename);
}
}

Case 1:

CwDB db = new CwDB("src/cwdb.txt");

Case 2:

InteliCwDB idb = new InteliCwDB("src/cwdb.txt");

The problem is that case 1 works perfectly, but case 2 doesn't at all. Can you tell me what's wrong? (I don't get any error/exception, just the idb's list is empty, when db's list has ober +1k elements...)

Answer 1

You say that:

1. There are no exceptions / stack traces.
2. The dict list in the created InteliCwDB instance is empty.

If the superclass constructor somehow didn't run, you would have an instance with a dict that was null .

If some other exception was thrown and not caught, then you wouldn't have a InteliCwDB to examine.

So on the face of it, this can only mean that the constructor is running , but the file it reads is empty. In other words you have two different "src/cwdb.txt" files ... in different directories.

---

Other explanations involve questioning your evidence; eg

• You are describing the symptoms inaccurately.
• The code you are actually running is substantially different to what you are showing us; eg there is some other code that is leaping in and emptying the dict after the constructor has created and filled it. (You haven't declared dict to be private ...).
  [ UPDATE - this was the explanation: see the OP's comments. He had overridden add in the subclass, and that's where the bug was. ]
• The code you are running doesn't match your source code; ie you are not rebuilding / redeploying properly.

---

My advice would be to recheck your processes and your evidence. And if that doesn't help, then run the application using a debugger, set a breakpoint on the constructor, and single step it so that you can work out what is really happening.

Answer 2

You should add a catch (Exception e) to your try-catch for the purposes of debugging. An exception that isn't an IOException might be causing you problems. So, try like this:

public CwDB(String filename){
    this.dict = new LinkedList<Entry>();
    try{
        FileReader fr = new FileReader(filename);
        BufferedReader br = new BufferedReader(fr);
        String w = null;
        while((w = br.readLine()) != null ){
            String c = br.readLine();
            this.add(w,c); //adds new Entry to dict
        }
        br.close();
        fr.close();
    }catch(IOException e){
        e.printStackTrace();
    }catch(Exception e){
        e.printStackTrace();
    }
}