Empty ArrayList fed by tokens

[Frank Poupard]

Hello, in the following program I'm looking for matches between some key words and some words contained in an array. The matches are expected to feed an ArrayList, which is unfortunately empty at the end. For example, if the input is

"add, whatever, mul"

, I expect to have

"add" and "mul"

as ouptut. It's a bit dummy for the moment but I woud like to make it work before any improvement. Thanks for your help.

public class Token {

	String[] operation = { "add", "sub", "mul", "div" };

	public ArrayList<String> toParse(String[] words) {

		ArrayList<String> expression = new ArrayList<String>();

		for (int i = 0; i < words.length; i++) {

			for (int j = 0; j < operation.length; j++) {

				if (words[i] == operation[j]) {
					expression.add(words[i]);
				}
			}
		}

		System.out.println("here are the matches terms :");
		for (String item : expression) {
			System.out.println(item);
		}

		return expression;

	}

}

public class Main {

	public static void main(String[] args) {

		Token tkn = new Token();
		System.out.println("Enter some input :");
		Scanner input = new Scanner(System.in);
		String toTokenize = input.nextLine();
	        String[] tokenized = toTokenize.split(" ");
		tkn.toParse(tokenized);
		
	}
}

[Stephan van Hulst]

Frank, Strings are objects, and as such the == operator performs identity comparison, not value comparison.

You should get into the habit of avoiding == when not dealing with primitives or enums.

[Frank Poupard]

My bad, thank you very much !