Java - 保存到文本文件

Question

我正在开发一个小型图书馆应用程序，它允许用户存储、借用、归还和删除技术手册。

我几乎完成了应用程序，现在我希望一旦用户从主菜单中选择选项 1，就可以将库自动保存到外部 txt 文件中，以查看整个库。我试图实现正确的代码，但现在没有创建文本文件。

这是我的手册课程中的相关代码：

            if(Menu.menuChoice == 1 && Library.ManualList.size() > 0){                      
                Library.displayManualList();
                Menu.displayMenu();
                try {
                    FileWriter fw = new FileWriter("Library.txt");
                    PrintWriter pw = new PrintWriter(fw);

                    pw.println(Library.ManualList);

                    pw.close();
                } catch (IOException e) {
                    out.println("Error! Library unable to save.");
                }
            }

            if(Menu.menuChoice == 1 && Library.ManualList.isEmpty()){
                System.out.println(Messages.addManualFirst);
                Menu.displayMenu();
            }

如果需要，这是我的整个库类：

public class Library {  

/** The Manual choice. */
public static int ManualChoice;

static String returnManualTitle;

/** The status1. */
static String status1 = "Available";

/** The status2. */
static String status2 = "Borrowed"; 

/** The Manual list. */
static ArrayList<Manual> ManualList = new ArrayList<Manual>();
static ArrayList<Manual> borrowedManuals = new ArrayList<Manual>();


/**
 * Adds the Manual.
 */
static void addManual(){
    Manual newManual = new Manual(); //create new Manual object with status "Available."
    newManual.createManual();
    ManualList.add(newManual);//add the Manual to the ManualList ArrayList.
    System.out.println("\n\n--------------------------------------------------------------------------");
    System.out.println("\n                          Manual added to library!\n");
    System.out.println("--------------------------------------------------------------------------\n");
}

/**
 * Display Manual list.
 */
static void displayManualList(){
    if (ManualList.isEmpty()){//If the library is empty, it goes back to main menu and choice.
        System.out.println("-------------------------------------------------------------");
        System.out.println(Messages.empltyLibraryMessage + Messages.tryAgainMessage);
        System.out.println("-------------------------------------------------------------");
        Menu.menuChoice = 7;

    } else {    
        System.out.printf("\n\nHere are the Manual/s currently stored in the library:\n\n\n");
        for (int i = 0; i < ManualList.size(); i++){
            System.out.printf("-------------------- Index Number: %s --------------------\n",i);
            System.out.println(ManualList.get(i).displayManual());  
            System.out.println("---------------------------------------------------------\n");
        }//End of For Loop.         
    }// End of Else Statement.          
}//End of if Statement.

static void displayBorrowedManuals(){
    if (ManualList.isEmpty()){//If the library is empty, it goes back to main menu and choice.
        System.out.println("-------------------------------------------------------------");
        System.out.println(Messages.empltyLibraryMessage + Messages.tryAgainMessage);
        System.out.println("-------------------------------------------------------------");
        Menu.menuChoice = 7;

    } else {                    
        for (int i = 0; i < borrowedManuals.size(); i++){
            System.out.printf("-------------------- Index Number: %s --------------------\n",i);
            System.out.println(borrowedManuals.get(i).displayManual()); 
            System.out.println("---------------------------------------------------------");
        }//End of For Loop.         
    }// End of Else Statement.          
}//End of if Statement.
/**
 * Borrow Manual.
 */
public static void borrowManual(){
    if(ManualList.size() > 1){
        displayManualList();
    }
    else if(ManualList.size() == 1){
        ManualList.get(ManualChoice).status = "Borrowed";
        ManualList.get(ManualChoice).borrower = User.userName;
        ManualList.get(ManualChoice).borrowDate = "Today.";
        ManualList.get(ManualChoice).returnDate = "In two weeks.";
        borrowedManuals.add(ManualList.get(ManualChoice));
        System.out.printf("\n\nThere is only 1 manual present in the library.\n\nBecause of this, it has been automatically borrowed for you.\n\nHere is the manual which has been borrowed:\n\n %s\n\n", ManualList.get(ManualChoice).displayManual());
        System.out.println("Please return the Manual within two weeks!\n");
    }
    //register user's Manual choice.
    ManualChoice = (Console.readInteger(Messages.enterManualIndexMessage, Messages.ManualIndexNotInListMessage, 0, Library.ManualList.size() - 1));

    borrowLoop:
    while(Menu.menuChoice == 3){
        //Check if the Manual to be borrowed is available.
        //ManualChoice = (Console.readInteger(Messages.enterManualIndexMessage, Messages.ManualIndexNotInListMessage, 1, Library.ManualList.size()));

        if ((ManualList.get(ManualChoice).status.equalsIgnoreCase(status1)) && (ManualList.size() >= ManualChoice)){
            //Print the borrowed Manual information and change the Manual status to borrowed.
            ManualList.get(ManualChoice).status = "Borrowed";
            ManualList.get(ManualChoice).borrower = User.userName;
            ManualList.get(ManualChoice).borrowDate = "Today.";
            ManualList.get(ManualChoice).returnDate = "In two weeks.";
            //Add the borrowed Manual to the borrowedManuals arraylist:
            borrowedManuals.add(ManualList.get(ManualChoice));

            System.out.println("\n--------------------------------------------------------------------------");
            System.out.println("\n                             Manual borrowed!\n");
            System.out.println("--------------------------------------------------------------------------\n");
            break borrowLoop;

        }else if(ManualList.get(ManualChoice).status.equalsIgnoreCase(status2) && ManualList.size() >= ManualChoice){
            System.out.println("\n--------------------------------------------------------------------------");
            System.out.println("\n            "
                    + " The Manual you wish to borrow is already on loan.");
            System.out.println("\n--------------------------------------------------------------------------\n");
            break borrowLoop;

        }else if(ManualChoice > ManualList.size()-1){
            System.out.println(Messages.noSuchManualMessage);
            break borrowLoop;
        }
    }
    Menu.displayMenu();
}

/**
 * Return Manual.
 */
static void returnManual(){
    System.out.printf("\n\nHere are the Manual/s currently out on loan:\n\n");

    if(borrowedManuals.size() > 0){
    for (int i = 0; i < borrowedManuals.size(); i++)
        System.out.println(borrowedManuals.get(i).displayManual());
        returnManualTitle = Console.readString(Messages.enterManualSerial, Messages.tooShortMessage, 3);
    }

    int x = 0;
    boolean serialExistance = false;
    while (x < ManualList.size()){//Search for the Manual by title, if it exists change it's status,
                                //it's borrower and borrowDate.

        if (ManualList.get(x).serial.equalsIgnoreCase(returnManualTitle)){

            ManualList.get(x).status = "Available";
            ManualList.get(x).borrower = "N/A";
            ManualList.get(x).borrowDate = "N/A";
            ManualList.get(x).returnDate = "N/A";

            int p = 0;
                while (p < borrowedManuals.size()) {
                    Manual borrowed = borrowedManuals.get(p); // guessing the name of this class
                    if (borrowed.serial.equalsIgnoreCase(returnManualTitle)) {
                        borrowedManuals.remove(p);
                        break;
                    }
                    p++;
                }               
            System.out.println(Messages.successReturnMessage);
            serialExistance = true;

            break;//if a title is found, break out of the loop and display choice menu.
        }
        x = x+1;
    }//end of while loop.
    if(serialExistance == false){
        boolean repeatReturnManual = Console.readYesNo("\n--------------------------------------------------------------------------" + "\n\nThe Manual with the title "+"\""+returnManualTitle +"\""+ " wasn't found!"
                                                        +"\n\nDo you want to try again? (Y/N):\n");
        System.out.println("\n--------------------------------------------------------------------------");
        if(repeatReturnManual){
            returnManual();
        }
    }else if(serialExistance){
        Menu.menuChoice = 7;
    }               
}

/**
 * Removes the Manual.
 */
public static void removeManual(){

    displayManualList();

    ManualChoice = Console.readInteger(Messages.enterRemoveManualIndex ,Messages.ManualIndexNotInListMessage, 0, ManualList.size());        
    int p = 0;
    while (p < borrowedManuals.size()){//Search for the Manual by title, if it exists change it's status,
        //it's borrower and borrowDate.

        if (borrowedManuals.get(p).title.equalsIgnoreCase(returnManualTitle)){

            borrowedManuals.remove(p);
        }
    }               
    ManualList.remove(ManualChoice);
    System.out.print(Messages.successRemovedManualMessages);
    Menu.menuChoice = 7;
}

/**
 * Empty library.
 */
static void emptyLibrary(){
    System.out.println("\n                                 WARNING!");
    System.out.println("\n           You have chosen to delete all Manuals in the library.\n"); 
    System.out.println("--------------------------------------------------------------------------");
    boolean emptyLibraryChoice = Console.readYesNo("\nAre you sure you wish to destroy the library? (Y/N): ");
    System.out.println("\n--------------------------------------------------------------------------");
    if(emptyLibraryChoice){
        Library.ManualList.clear();
        System.out.println(Messages.successEmptyLibraryMesssage);
        System.out.println("--------------------------------------------------------------------------\n\n");
        Menu.menuChoice = 7;
        }

}

}

如果有人知道我如何将库的内容保存到文本文件中，请告诉我，感谢您的帮助 :) 我对 Java 还很陌生，所以如果我遗漏了所需的代码，请告诉我知道！

Answer 1

尝试一个循环来获取库中的每一个元素。

for(int i=0; i<Library.ManualList.size(); i++)
     pw.println(Library.ManualLis.get(i));
pw.close();