Thread: how to convert a input array of type Strings to a class type

thanks for replying..
@Kevin

while giving input it is either a type of String or int or char.And it gives a error (cannot convert from String to passenger). So i think i need to give the input in passenger type but i dont know how do i achieve that. If u can plz give an example it would really help.[COLOR="Silver"]

--- Update ---

Originally Posted by Junky

You might want to give the Passenger array variable a name as well!

I tried but it still gives the same error (cannot convert from String to passenger).If u have any idea how to correct it....if possible an example would suffice.

Post your updated code correctly using code or highlight tags which are explained near the top of this link.

Originally Posted by GregBrannon

Post your updated code correctly using code or highlight tags which are explained near the top of this link.

QUESTION
Define a class Passenger having the fields name (String), age (int), gender (char : M/F), weight (int). Define 2 constructors for this class, one with parameters and one which has no parameters.

Also define a class Train in which there are the following functions. Note that there are no fields in the class Train.

- int getTotalWeight(Passenger[] passengers) - returns the total weight of all the passengers in the input

DOUBT
if i take input it is in (String or char or integer )....but we have to use this input to find total weight of all passengers.......and the method is
getTotalWeight(Passenger [] passengers)

which gives the error(cannot convert from String to Passenger).So how i take this input and use it to find the total weight of the passengers.

WHAT I EXPECT
i want you to tell what input i should take(if my input is wrong) or how can i use this input to in class train to find total weight.

MY INPUT(if this type of input is correct...plz check)
("A,21,M,62","B,45,M,78","C,22,F,56","D,10,F,30"," E,8,F,29")

MY CODE

  class Passenger{ String name; int age; char gender; int weight;   public Passenger(){ } public Passenger(String name,int age,char gender,int weight){ this.name=name; this.age=age; this.gender=gender; this.weight=weight; }   }   class Train { public int getTotalWeight(Passenger[] passengers) { int total=0;   //(here will be the code)   return total;   } } public class TestTrain { //main class   public static void main(String[] args) { //main method // TODO Auto-generated method stub Train test =new Train(); //i initialize my input String [] passengers = {"A,21,M,62","B,45,M,78","C,22,F,56","D,10,F,30","E,8,F,29"}: tets.getTheWeight(passengers); // here i get error

Nice post! Very helpful. Thanks for taking the time to be thorough, clear, and posting the code correctly.

First, let's eliminate the syntax errors from the code you posted, since we don't know if those are included in your environment or copy/paste errors, etc.

1. The line

Passenger [] passengers = {"A,21,M,62","B,45,M,78","C,22,F,56","D,10,F,30"," E,8,F,29"}:

appears to end in a colon rather than a semicolon. Fix that.

2. The code you posted is missing two close braces, '}', at the end. Please add those.

3. Then, in the line "// here i get error", there is a typo. If you were to mouse over the red line (if that's what you're seeing), you will get an explanation that you can mouse into and even select and copy. In my IDE, I get the error:

tets cannot be resolved

tets? What is that? The compiler doesn't know, but it appears to be a typo. Fix that.

4. Once that error is corrected, a new error appears in the same line:

The method getTheWeight(String[]) is undefined for the type TestTrain

Similar to #3, what is "getTheWeight()"? The compiler doesn't know what that is, and it's more than a typo this time. It's the name of a method that either doesn't exist or there's a name mixup. Fix that.

Once those errors are fixed, return with your updated code and the questions you still have.

We can't get to your original question of "So how i take this input and use it to find the total weight of the passengers?" until you fix the above errors and define your design a bit more. For example,

Passenger [] passengers = {"A,21,M,62","B,45,M,78","C,22,F,56","D,10,F,30"," E,8,F,29"}; // with semicolon

doesn't make sense. You might instead, define a string of Passenger attributes:

String [] passengerData = {"A,21,M,62","B,45,M,78","C,22,F,56","D,10,F,30"," E,8,F,29"};

and then send each element of that String object to a Passenger() constructor in a loop to create Passenger objects

Passenger passenger[i] = new Passenger( passengerData[i] );

That approach will require modifying the existing Passenger() constructor or adding a new one - not a big deal.

Come back with updated code when you're ready to move on. If you're stuck and don't get what I've suggested, then ask more questions about that.

MY INITIAL QUESTION

Define a class Passenger having the fields name (String), age (int), gender (char : M/F), weight (int). Define 2 constructors for this class, one with parameters and one which has no parameters.

Also define a class Train in which there are the following functions. Note that there are no fields in the class Train.

- int getTotalWeight(Passenger[] passengers) - returns the total weight of all the passengers in the input

THE ERROR I AM STILL GETTING

The method getTotalWeight(Passenger[]) in the type Train is not applicable for the arguments (String[]).

EXPLANATION ABOUT THE QUESTION

we need to use the input to find the total weight of all passengers in class TRAIN.

MY MAIN DOUBT
how to remove the error i am getting???

CODE

  package module4a;     class Passenger{ String name; int age; char gender; int weight;   public Passenger(){ } public Passenger(String name,int age,char gender,int weight){ this.name=name; this.age=age; this.gender=gender; this.weight=weight; }   }   class Train { public int getTotalWeight(Passenger[] passengers) { int total =0;   // here we have to write code     return total;   } } public class TestTrain {   public static void main(String[] args) { // TODO Auto-generated method stub Train test =new Train(); String[] passengers ={"A,21,M,62","B,45,M,78","C,22,F,56","D,10,F,30","E,8,F,29"}; test. getTotalWeight( passengers); }   }

Beautiful! Nice corrections so far.

The signature of the getTotalWeight() method was specified by the assignment, so you can't mess with that. Since that's the reason for the error. you'll have to prepare the parameter in the statement,

test. getTotalWeight( passengers);

to agree with the getTotalWeight() method's signature, i.e. pass it an array of Passenger objects rather than an array of String objects. The question is then, how to create an array of Passenger objects from what you have? As I suggested before, the passenger data contained in the String array you have now can be used to create Passenger objects. The Passenger() constructor is not specified by the assignment, so you could have a constructor with the signature:

public Passenger( String passengerData ) { }

and a call to create Passenger objects:

passengers[i] = new Passenger( passengerData[i] );

The above statement would be in a for() loop in your current main() method, using the String array passengers which I renamed for clarity, passengerData, to get you started, main() would look something like:

public static void main(String[] args) { Train test =new Train(); String[] passengerData ={"A,21,M,62","B,45,M,78","C,22,F,56","D,10,F,30","E,8,F,29"}; Passenger[] passengers = new Passenger[passengerData.length];   // a loop to make Passenger objects out of passengerData and store them // in a Passenger array for ( int i= 0 ; i < passengerData.length ; i++ ) { // create a Passenger object and store in passengers array (the statement I showed you above) }   test. getTotalWeight( passengers); }

You'll have to modify the Passenger() constructor to accept the String argument and then parse the String argument into the parts and types needed for the Passenger fields. I recommend you look at the String.split() method to do part of that and then convert the parsed elements into the types needed.

Make some progress and come back when you need more help. I can't do much more without doing the whole thing for you.

Hints: You will need at least one other method in Passenger to complete the needed code in the Train method.

made some progress...but still a lot to do...

giving my code here...

package module4a;   class Passenger{ String name; int age; char gender; int weight;   public Passenger(){ }   public Passenger(String passengerData){   String[] data = passengerData.split(",");	Passenger pass = new Passenger();	pass.name = data[0];	pass.age = Integer.parseInt(data[1]);	pass.gender = data[2].charAt(0);	pass.weight = Integer.parseInt(data[3]); } }   class Train { public int getTotalWeight(Passenger[] passengers) { int total=0; for(int i =0;i<passengers.length;i++){	Passenger pass = new Passenger();	total =total+pass.weight; } System.out.println(total); return total;   } } public class TestTrain {   public static void main(String[] args) { // TODO Auto-generated method stub Train test =new Train(); String[] passengerData ={"A,21,M,62","B,45,M,78","C,22,F,56","D,10,F,30","E,8,F,29"}; Passenger[] passengers = new Passenger[passengerData.length]; for ( int i= 0 ; i < passengerData.length ; i++ ){ passengers[i]= new Passenger(passengerData[i]); } test. getTotalWeight( passengers);   }   }

Pretty good. You've essentially answered your initial question, but you demonstrated that you're missing some basic concepts.

You've misunderstood the use of a constructor as shown by the changes you made to the Passenger() constructor. If you write a constructor that creates an instance of the class using a 'new' statement, you're probably doing something wrong or very special, like writing a copy constructor. In this case, the Passenger object being created by the Passenger() constructor happens when you call the constructor using the 'new' statement in the main() method.

How to fix: Eliminate the 'pass' object entirely.

There's no reason for the Train class to be creating passengers. It might be helpful if you wrote a comment at the beginning of each of the classes that describes what they do. Get rid of the 'pass' object and use the weight of each of passengers[] elements to find the total weight.

Keep chuggin'.

I have coded the Passenger construct but i dont understand how to add the total weight of all the passengers ...if you could give some hint...

  package module4a;   class Passenger{ String name; int age; char gender; int weight;   public Passenger(){ }   public Passenger(String passengerData){ String data[] = passengerData.split(","); this.name = data[0]; this.age = Integer.parseInt(data[1]); this.gender= data[2].charAt(0); this.weight = Integer.parseInt(data[3]); }   class Train { public int getTotalWeight(Passenger[] passengers) { int total=0; for(int i =0;i<passengers.length;i++){  	total =total+passengers[i].weight; }   return total;   } } public class TestTrain {   public void main(String[] args) { // TODO Auto-generated method stub Train test =new Train(); String[] passengerData ={"A,21,M,62","B,45,M,78","C,22,F,56","D,10,F,30","E,8,F,29"}; Passenger[] passengers = new Passenger[passengerData.length]; for ( int i= 0 ; i < passengerData.length ; i++ ){ passengers[i]= new Passenger(passengerData[i]);   } test. getTotalWeight( passengers);   } } }

Much better on the constructor. Note that the keyword 'this' is not required, because there is no confusion with local variables of the same name. Leaving the 'this' is also okay, it's just not required.

Are you running, or trying to compile and run, the program just as you've posted it? If so, you're surely getting errors. Resolve those, post them if you need help resolving them. Reason: A top-level public class with a static main() method is required as the program's entry point, and that doesn't exist in what you've posted. Your indentation is off, so while the class TestTrain may appear to be at the top level because it begins in column 0, it is indented improperly and should not start in column 0. And someone removed the modifier 'static' from the main() method signature.

As for your total weight question, you have all of the the code needed, except you need to output the results of the last line in your main() method - print it.

A more appropriate way to access each passenger's weight attribute stored in the Passenger field, weight, while preserving encapsulation is to is to add an accessor (or getter) method to the Passenger class. In this case, the method would have the signature:

public int getWeight()

Surely, you've heard of this. An alternative to what you have would be to add the method getWeight() to Passenger and then in the Train.getTotalWeight() method, obtain the weight of each passenger object in the loop using the getWeight() method, storing the sum of the weights in total, just as you're doing now.

when i write static in the code it gives following error.....and i am having difficulty in correcting that...

error

The method main cannot be declared static; static methods can only be declared in a static or top level type.

  package module4a;   class Passenger{ String name; int age; char gender; int weight;   public Passenger(){ }   public Passenger(String passengerData){ String data[] = passengerData.split(","); this.name = data[0]; this.age = Integer.parseInt(data[1]); this.gender= data[2].charAt(0); this.weight = Integer.parseInt(data[3]); }   class Train { public int getTotalWeight(Passenger[] passengers) { int total=0; for(int i =0;i<passengers.length;i++){  	total =total+passengers[i].weight; }   return total;   } } public class TestTrain {   public static void main(String[] args) { // TODO Auto-generated method stub Train test =new Train(); String[] passengerData ={"A,21,M,62","B,45,M,78","C,22,F,56","D,10,F,30","E,8,F,29"}; Passenger[] passengers = new Passenger[passengerData.length]; for ( int i= 0 ; i < passengerData.length ; i++ ){ passengers[i]= new Passenger(passengerData[i]);   } test. getTotalWeight( passengers);   } } }

Notice the words "top level" in the error message? Sound familiar? I explained the significance of the top-level public class and why it appears you have one but don't in Post #13. Indent your code properly and then rearrange your code so that you have a top-level public class with a main() method for the program's entry point.

i have tried this question in a different way....is it correct??...but there are some mistakes due to which i am not getting the output.....it would be great if you could point out to me...

  package module4a;   class Passenger{ String name; int age; char gender; int weight;   public Passenger(){ }   public Passenger(String name,int age,char gender,int weight){ this.name = name; this.weight = weight; Passenger passengers3 = new Passenger("A",23,'F',45); Passenger passengers1 = new Passenger("B",13,'M',55); Passenger passengers2 = new Passenger("C",33,'M',65); Passenger[] passengers = {passengers3,passengers1,passengers2}; } }   class Train { public int total(Passenger[] passengers) { Passenger object = new Passenger(); int total =0; for(int i=0;i<passengers.length;i++){ total = total+object.weight; } System.out.println(total); return total;   }   }   public class TestTrain {   public static void main(String[] args) { // TODO Auto-generated method stub Train test = new Train(); System.out.println();     } }