Java包含方法

Question

I have a problem with a contains (...) method from List <...> class. I'm trying to check if a expression (that is loaded from user input) already exist in a List, but if I entered same name as twice, it said there's nothing same in the List. Please help, there's source code:

boolean checker;

checker = expressions.contains(line[1]);

if (checker == true) {
    System.err.println("This expression has already been declared!");
    return index;
}

PS: line[1] is a second index in array from main function that stores user-entered line split by whitespaces. (First index of line need to be always 'var', and second is any word that cannot be twice in the List)

Answer 1

Your list may not have exact same string as provided in the input which may be due to white spaces. Try trimming the input and then call contains

 checker = expressions.contains(line[1].trim());