Java Switch菜单错误以及如何从另一个类调用方法

Question

Hi Im currently learning Java and Im doing an assignment where I need to *create a Menu that calls several methods. I have 3 classes (Contacto,Agenda and Principal). My assignment is trying to evaluate Constructors and Arrays and some other basic theory.

My menu error is: Principal.java:34: error: cannot find symbol while(opcion!=4).* 

I already check and my variable "opcion" is declared.

public class Principal{

private static void imprimeMenu(){
    Scanner input = new Scanner(System.in);

    String mainMenu = ("Choose an option from the menu: \n"
                        + "1. Add contact\n"
                        + "2. Find contact\n"
                        + "3. Search contact\n"
                        + "4. Exit");

    do{
    System.out.println(mainMenu);
    int opcion = input.nextInt();

    switch(opcion){
        case 1:
            break;
        case 2:
            System.out.println("Search");
            break;
        case 3:
            System.out.println("Erase");
            break;
        default:
            System.out.println("Command not recognize");
            break;
        }
    }
    while(opcion!=4);
}

public static void main(String[] args){
    imprimeMenu();      
}
}

And inside the my cases I need to call 3 methods (Add, Search and Erase contacts) that are inside a class called Agenda. The 3 methods are void and receive a parameter. I tried but I get an error where it says I need some parameters:

case 1:
    Agenda.addContacto(); and also tried Agenda.addContacto(contacto);

My Agenda class looks like this

public class Agenda{
private Contacto [] contactos;
private int numContactos;


public Agenda(){
    this.contactos = new Contacto[10];
    this.numContactos = 0;
}

public Agenda(int x){
    this.contactos = new Contacto[x];
    this.numContactos = 0;
}

public void addContact(Contacto contact){
    if(numContactos<contactos.length){
        this.contactos [numContactos] = contact; 
        numContactos+=1;
    } 
          }

Answer 1

Your problem is that opcion is defined inside the loop, so it's scope ends before the closing while .

Move the definition outside the loop to fix the problem:

int opcion = 0;
do{
    System.out.println(mainMenu);
    opcion = input.nextInt();

    switch(opcion){
        case 1:
            break;
        case 2:
            System.out.println("Search");
            break;
        case 3:
            System.out.println("Erase");
            break;
        default:
            System.out.println("Command not recognize");
            break;
        }
} while(opcion!=4);

The correct call of Agenda.addContacto method is indeed Agenda.addContacto(contacto) . You need to make sure that contacto is set to an instance of Contacto object before making the call.

Answer 2

You have 2 issues with these programme

1.You need to declare option variable before the while loop.

2.If you want to call Agenda.anyMethod() you need to create an instance/object of the class otherwise you can declare the class Agenda as static.then you can directly call the method as Agenda.addContacto();