java - 将数据传递给方法

Question

我试图将“personListToPrint”传递给 main.java 并在使用开关 3 时让它出现，但是它不起作用。我不知道如何解决这个问题。有什么想法吗？？

这里是main.java

package hartman;


import java.util.ArrayList;
import java.util.Scanner;

public class Main {

public static void main(String[] args) {
    Printer.printWelcome();

    Scanner keyboard = new Scanner(System.in);
    ArrayList<Person> personList = new ArrayList<>();
    boolean keepRunning = true;
    while (keepRunning) {
        Printer.printMenu();
        Printer.printPrompt("Please enter your operation: ");

        String userSelection = keyboard.nextLine();

        switch (userSelection) {
        case "1":
            Database.addPerson(personList);
            break;
        case "2":
            Database.printDatabase(personList);
            break;
        case "3":
            Printer.printSearchPersonTitle();
            String searchFor = keyboard.nextLine();
            Database.findPerson(searchFor);
            Printer.printPersonList(personListToPrint);
            break;
        case "4":
            keepRunning = false;
            break;
        default:
            break;
        }
    }

    Printer.printGoodBye();
    keyboard.close();
  }

 }

这里是database.java

package hartman;

import java.util.ArrayList;
import java.util.Scanner;

public class Database {
static Scanner keyboard = new Scanner(System.in);
private static ArrayList<Person> personList = new ArrayList<Person>();

public Database() {

}

public static void addPerson(ArrayList<Person> personList) {
    Printer.printAddPersonTitle();
    Printer.printPrompt("  Enter first name: ");
    String addFirstName = keyboard.nextLine();

    Printer.printPrompt("  Enter last Name: ");
    String addLastName = keyboard.nextLine();

    Printer.printPrompt("  Enter social Security Number: ");
    String addSocial = keyboard.nextLine();

    Printer.printPrompt("  Enter year of birth: ");
    int addYearBorn = Integer.parseInt(keyboard.nextLine());

    System.out.printf("\n%s, %s saved!\n", addFirstName, addLastName);
    Person person = new Person();
    person.setFirstName(addFirstName);
    person.setLastName(addLastName);
    person.setSocialSecurityNumber(addSocial);
    person.setYearBorn(addYearBorn);
    personList.add(person);
}

public static void printDatabase(ArrayList<Person> personList) {
    System.out
            .printf("\nLast Name           First Name           Social Security Number  Age\n");
    System.out
            .printf("=================== ===================  ======================  ===\n");
    for (Person p : personList) {

        System.out.printf("%-20s%-21s%-24s%s\n", p.getLastName(),
                p.getLastName(), p.getSocialSecurityNumber(), p.getAge());

    }

}

public static ArrayList<Person> findPerson(String searchFor) {
    ArrayList<Person> matches = new ArrayList<>();
    for (Person p : personList) {
        boolean isAMatch = false;

        if (p.getFirstName().equalsIgnoreCase(searchFor)) {
            isAMatch = true;

        }
        if (p.getLastName().equalsIgnoreCase(searchFor)) {
            isAMatch = true;

        }
        if (p.getSocialSecurityNumber().contains(searchFor)) {
            isAMatch = true;
            ;
        } else if (String.format("%d", p.getAge()).equals(searchFor))
            if (isAMatch) {

            }
        matches.add(p);
        Printer.printPersonList(matches);
    }
    return matches;

}

}

最后，这是printer.java

package hartman;

import java.util.ArrayList;

public class Printer {
public static void printWelcome() {
    System.out.printf("WELCOME TO PERSON DATABASE!\n");
}

public static void printGoodBye() {
    System.out.printf("\nGOOD BYE!!\n");
}

public static void printMenu() {
    System.out.printf("\nMain Menu\n");
    System.out.printf("---------\n\n");
    System.out.printf("  1. Add a new Person to the database.\n");
    System.out.printf("  2. Print the database.\n");
    System.out.printf("  3. Search for a person in the database.\n");
    System.out.printf("  4. Exit the application.\n");
    System.out.printf("\n");
}

public static void printPrintMenu() {
    System.out.printf("Print\n\n");
}

public static void printAddPersonTitle() {
    System.out.printf("\nAdd Person to Database\n\n");

}

public static void printPrompt(String promptForWhat) {
    System.out.printf("%s", promptForWhat);
}

public static void printPersonSaved(Person personSaved) {
    System.out.printf("%s", personSaved);
}

public static void printSearchPersonTitle() {
    System.out.printf("\nSearch for Person in Database\n\n");
    System.out.printf("Enter search value: ");
}

public static void printPersonList(ArrayList<Person> personListToPrint) {

    System.out
            .printf("\nLast Name           First Name           Social Security Number  Age\n");
    System.out
            .printf("=================== ===================  ======================  ===\n");
    for (Person p : personListToPrint) {

        System.out.printf("%-20s%-21s%-24s%s\n", p.getLastName(),
                p.getLastName(), p.getSocialSecurityNumber(), p.getAge());

    }

}
}

Answer 1

您没有定义变量

personListToPrint

将案例 3 替换为下一个

case "3":
    Printer.printSearchPersonTitle();
    String searchFor = keyboard.nextLine();
    ArrayList<Person> personListToPrint = Database.findPerson(searchFor);
    Printer.printPersonList(personListToPrint);
    break;

现在可以编译了