Java程序根据字符串比较不退出

Question

我是一名新手，正在做一项向我们介绍如何使用 Java 中的文件的家庭作业，我正在尝试为用户提供一个选项，以便在他们未能成功创建文件时提前退出(例如，如果他们没有写入磁盘的权限)。这是我试图从中结束程序的 try catch block :

    // Loop used to repeat try catch block until a file is successfully created/opened
    FileWriter FW = null;       // Create & initialize the FW object outside of the loop 
                                // to ensure availability in the correct scope
    boolean success = false;
    while (success == false) {
        // Try catch block for handling possible exception thrown by the 
        // FileWriter constructor
        try {
            FW = new FileWriter(fileName);
            success = true;
        } 

        // Catch allows the user to attempt to rename file and includes option
        // to exit program immediately (presumably after multiple failed attempts)
        catch (IOException e) {
            String failString = "exit";
            fileName = (String)JOptionPane.showInputDialog(
                    "There was an error creating your file.  Please\n" +
                    "ensure you have permission to write to the directory\n" +
                    "and then re-enter your desired file name.  Please do\n" +
                    "not attempt to specify a directory.  Please do not\n" +
                    "use special characters.  Type 'exit' to end the\n" +
                    "program now.");
            if (fileName != failString) {
                fileName = fileName + ".txt";
            }

            else {
                JOptionPane.showMessageDialog(null, "Exiting...", "EXITING", 1);
                System.exit(0);
            }
        }
    }

我认为应该发生的是用户输入术语“exit”作为新文件名，程序将立即退出。但是，当我进入 exit 时，程序只是创建一个名为 exit.txt 的文件并继续执行。我很茫然。

关于错误的任何想法或关于更好的方法的建议？

Answer 1

使用 equals() 比较字符串，而不是 != 或 ==。

所以你需要

if (!fileName .equals(failstring)) {
  fileName = fileName + ".txt";
} else {
  System.exit(1);
}

有关详细信息，请参阅 Java 教程:http://docs.oracle.com/javase/tutorial/java/data/comparestrings.html

顺便说一句:通常使用“积极”的表达方式比使用消极的表达方式更好(人脑可以更好地应对它们)。所以推荐使用:

if (fileName .equals(failstring)) {
  System.exit(1);
} else {
  fileName = fileName + ".txt";
}

代替