Java Method Design query

Question

This is a fairly rudimentary question but one that I am kind of on the fence about. Lets say I have a class A and it has methods method1,method2,method3,method4 and a main method.

method2 is only invoked by method1; method4 is only invoked by method3.

The solution says to invoke the method1 from main and also method2 from main and same with method3 and 4.

So isn't it bad design to have the main method invoke method1, and method2 explicitly? What is the point of having private methods in a class if you invoke them in the main method even though they are only dependent on a single method in the whole class?

Wouldn't it be cleaner to call method2 from method1 and method4 from method3 since in both cases the latter method is only invoked by the former?

I thought this was the whole point of helper methods, so that we are able to abstract away unnecessary details of the implementation.

Again my apologies for the simplicity of the question, I am quite new to java.

Class A{

 public static void main(String[] args){
    int x = method1()
    if ( x = 0){
                  //user wants to create a new account
    method2()
    }


 }

private static int method1(){ 
  //some code to check user login credentials in list of users
  //if login credentials fail,user is asked if they want to create a new account, if yes,
  //method 2 is invoked
  //return value is whether the user wants to create a new account or not.
}
private static void method2(){
   //creates new account for user and is only invoked by method1.
}

}

In the above case wouldn't it just be easier to call method2() from method1() instead of calling it in the main(). I would like to know if there are any advantages or disadvantages of this style of implementation.

I don't think there is enough context here to answer your question. You say "the solution says" - what solution? To what problem? — Greg Hewgill
– Greg Hewgill, Commented Aug 31, 2013 at 21:07
The problem has been updated and basic code is given above for the part of the problem that I am interested in. Basically it has to do with creating or validating user accounts based on the username and password entered by a particular user. — anonuser0428
– anonuser0428, Commented Aug 31, 2013 at 21:15

Greg Hewgill · Accepted Answer · 2013-08-31 21:23:10Z

In general terms, this is an exercise in separation of concerns. First, let's give your methods real names:

checkUserAccount(name, password)
addNewUserAccount(name)

Now, suppose you write checkUserAccount() so that it calls addNewUserAccount() if the user name is not found. In this case, the main program has no way of calling a function to just check the user credentials. The main program has no choice but to check the user account and then a new account will be added if the user isn't found. This is not very flexible if you decide to change things later.

On the other hand, if you separate these actions then the main program can decide what to do itself in the case where a user account is not found. You can then write code that looks something like what you showed:

if (checkUserAccount(name, password)) {
    // great! logged in
} else {
    addNewUserAccount(name);
}

This allows you to easily modify the main program if you choose to add a new feature. For example:

if (checkUserAccount(name, password)) {
    // great! logged in
} else {
    if (newUsersPermitted) {
        addNewUserAccount(name);
    } else {
        System.out.println("Sorry, this system is closed.");
    }
}

Of course, a real login system will have many more details to consider.

Thiago C. S Ventura · Accepted Answer · 2013-08-31 21:56:45Z

It's just a pseudocode, just to give you an idea.

public class User {

    String name;
    String username;
    String password;

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }

}

Here you can leave your queries

public class UserDAO {

    public Boolean checkUsername(User user){


        //here you use the object User
        //ex: user.username, user.password in your query

        String sql = "select bla bla bla";

        if(sql){

            //save something in log(just a example for a private method)
            saveLog();

            return true;
        }else{
            return false;
        }

    }

    private Boolean saveLog(){

        String sql = "insert bla bla bla";

        if(sql){
            return true;
        }else{
            return false;
        }


    }

}

Here is your main class

public class Test {


    public static void main(String[] args) {

        User u = new User();
        u.setUsername("john");
        u.setPassword("6876sdh");

        UserDAO dao = new UserDAO();
        Boolean ret = dao.checkUsername(u);

        if(ret){
            System.out.println("OK");
        }else{
            System.out.println("No Ok");
        }



    }

}

A full simple example: http://www.roseindia.net/tutorial/java/jdbc/dataaccessobjectdesignpattern.html

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