每个循环中缺少return语句

Question

I'm getting the error "Missing return statement" with this code:

public String getAuthorFullName(String title)
{
    for (Book authorName : inventory)
        if (authorName.getTitle() != null)
        {
            return authorName.getAuthor().getName().getFullName();
        } 
        else
        {
            return null;
        }
} 

I want to return o returns the full name of the author who wrote the book by this title or return null if there is no Book with this title, or if title is null or "".

I tried to put the code like this:

public String getAuthorFullName(String title)
{
    for (Book authorName : inventory)
        if (authorName.getTitle() != null)
        {
            return authorName.getAuthor().getName().getFullName();
        }
        return null;

But it always returns the first Author in the list...

Can somebody help me please? Thanks a lot.

Answer 1

Try something like this

public String getAuthorFullName(String title)
{
    for (Book authorName : inventory) {
        if (authorName.getTitle() != null && authorName.getTitle().equals(title)) {
            return authorName.getAuthor().getName().getFullName();
        }
    }
    return null;
}

and always use braces. It is much easier to live with them then without them.

Answer 2

Your first case is missing a return statement because it is. Consider having an empty inventory. So the for loop will make no runs and neither the if statement or the else statement will be executed. And then there is no return statement left.

Your second case has a return statement that is not part of the for loop and so a correct java syntax. BUT you only check if getTitle() != null . And thats true for every case a title has been set, even if it is empty.

The equality of Strings is checked with String.equals(String another) . So what you really want to do is:

public String getAuthorFullName(String title){
    for (Book authorName : inventory)
        if (authorName.getTitle() != null && authorName.getTitle().equals(title))
            return authorName.getAuthor().getName().getFullName();
    return null;
}

Answer 3

public String getAuthorFullName(String title) {
    for (Book authorName : inventory) {
        if (authorName.getTitle() != null && authorName.getTitle().equals(title)) {
            return authorName.getAuthor().getName().getFullName();
        } 
    }
    return null;
}