How do you go through ArrayList and find what is in the ArrayList using Scanner?

Question

I am making an ArrayList of cars and I am having trouble how to iterate through the ArrayList and print what I ask using a scanner. Example: I am looking for an Audi in the list, I want it to look through the ArrayList and if it is in the ArrayList print "We have a %s."

This is what I have so far: public class Main {

public static void main(String[] args) {
    ArrayList<String> car = new ArrayList<>();
    car.add("Audi");
    car.add("Chevrolet");
    car.add("Dodge");
    car.add("Ford");
    car.add("Honda");
    car.add("Toyota");
    car.add("Volkswagen");

    Scanner sc = new Scanner(System.in);
    String str = sc.nextLine();

    for(String name: car)
    {
        if(name == sc){
            System.out.printf("We have a %s.", sc);
        }
    }
}

}

Does this answer your question? [How do I compare strings in Java?](https://stackoverflow.com/questions/513832/how-do-i-compare-strings-in-java) — Ivar, Nov 29 '19 at 23:20
A string cannot be equal to a scanner. It can be equal to the string that you read with the scanner though. And hint: List has a contains() method. — JB Nizet, Nov 29 '19 at 23:20
`if(name == sc){`, No, you're trying to equate a String with a Scanner object, so that doesn't make logical or coding sense. You use the Scanner to extract Strings from a file or the user and then do things with the String. — Hovercraft Full Of Eels, Nov 29 '19 at 23:21

Stephen C · Accepted Answer · 2019-11-30T01:45:32.313

I think that real problem here¹ is that you don't have a clear understanding of what a Scanner does.

A Scanner reads characters from a stream (for example System.in) and turns them into various kinds of values; e.g. integers, floating point numbers, strings and so on. The basic model is:

call hasNextXXX to test if there is a XXX to read.
call nextXXX to read a XXX.

So you are trying to get a name of a car manufacturer from the Scanner. Assuming that car manufacturer names don't have spaces in them, what you are reading is a white-space delimited token. The method for reading a token is Scanner::next. It returns the token as a String with any leading or trailing whitespace removed.

Aside: String::nextLine would also work, except that it returns the complete line with all white space entered by the user before or after the name². If the user enters (for example) Ford with a space after it, then that won't match the value in your car list. To deal with that, you would need to do something like this:

    String str = sc.nextLine().trim();  // 'trim' removes leading and 
                                        // trailing whitespace; e.g. SP,
                                        // TAB, CR and NL characters.

Once you have the name as a String, you should String::equals to compare it against other strings. Comparing strings using == is incorrect in nearly all circumstances; see How do I compare strings in Java?

For a deeper understanding of Scanner, I recommend that you take the time to read the javadocs.

Your code doesn't do the above. Instead, it reads a line (i.e. str = sc.nextLine()) and doesn't use it. Then it uses == to test if the Scanner is equal to each String in your list. That fails, because a Scanner is not a String.

Aside: in Java, == for a reference type (i.e. for objects) means "is this the same object".

^{1 - The other possibility is that you didn't read the code that you had written carefully enough.}

^{2 - ... apart from the line separator sequence; i.e. CR, NL or CR + NL. This is removed automatically by nextLine: refer to the javadocs for more details.}

How do you go through ArrayList and find what is in the ArrayList using Scanner?

1 Answers1