死代码警告Java

Question

I have the following part of code:

public void deepSearch(File fileToLook,ArrayList<File> fileStorage,DefaultComboBoxModel<String> mod){
        if(fileToLook.isDirectory())
        {
            for(File f:fileToLook.listFiles())
                deepSearch(f,fileStorage,mod);
        }
        else if(fileToLook != null){
            fileStorage.add(fileToLook);
            mod.addElement(fileToLook.getName());
        }
        else
            System.out.println("Reached an end.");
    }

But eclipse gives me a dead code warning on this:

else
    System.out.println("Reached an end.");

Can you explain why this is happening.Thanks in advance

Answer 1

Well, fileToLook can't be null when the else statement is reached, since if it is null , the first condition will throw a NullPointerException .

It would make more sense to refactor the method, and avoid the potential NullPointerException :

if(fileToLook != null) {
    if(fileToLook.isDirectory()) {
        for(File f:fileToLook.listFiles())
            deepSearch(f,fileStorage,mod);
    } else {
        fileStorage.add(fileToLook);
        mod.addElement(fileToLook.getName());
    }
} else {
    System.out.println("Reached an end."); // not sure if you really need this
                                           // statement. It looks like a debug print to me
}

Answer 2

Well the null if (fileToLook != null) check is actually not needed, because if (fileToLook.isDirectory()) already throws a NullPointerException if it is null. The last else can thus never be reached.

Answer 3

The first if condition will throw a NullPointerException if fileToLook is null. The second branch is taken if it's not null. Therefore the third branch is never executed.

You might want to put the null check first.