java - 在方法内嵌套 while 循环后无法返回值

Question

添加第二个 while 循环(promptAddAgain)后，我在返回 DVD 对象时遇到问题。在添加 while 循环之前，该函数可以完美运行。编译期间出错 - 找不到符号:变量 currentDVD。

public DVDs getNewDVDInfo() {
    boolean keepRunning = true;
    boolean promptAddAgain = true;
    while (keepRunning) {
        String title = input.readString("Please enter the move title.");
        String releaseDate = input.readString("Please enter the release date.");
        String MPAArating = input.readString("Please enter the MPAA rating.");
        String directorName = input.readString("Please enter the director name.");
        String studio = input.readString("Please enter the name of the studio.");
        String userRating = input.readString("Please type in any comment you would "
                + "like to leave for this movie below.");

        DVDs currentDVD = new DVDs(releaseDate, MPAArating, directorName, studio, userRating);
        currentDVD.setTitle(title);

        while (promptAddAgain) {
            String userAns = input.readString("Would you like to add another DVD to the library?");
            if (userAns.equals("n")) {
                input.print("Thank you.  Returning to main menu.");
                keepRunning = false;
                promptAddAgain = false;
            } else if (userAns.equals("y")) {
                input.print("\n");
            } else {
                input.print("Unknown input, please try again.");
                keepRunning = false;
            }
        }
    }
    return currentDVD; //<--- error
}

Answer 1

发生错误的原因是 currentDVD 当前正在外部 while 循环内定义，但在它超出范围后您在该循环之外引用它。解决此问题的一种方法是在第一个 while 循环之前声明 currentDVD:

DVDs currentDVD = null;
while (keepRunning) {
    ...
}
return currentDVD;

请记住，使用上述方法时，您的 getNewDVDInfo() 方法可能会返回 null，因此调用者应该意识到这一点。