如何检查符号是否在用户输入上？

Question

I tried searching for an answer, but I don't know how to answer it. I tried making my own, but it show me this error:

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
    The method contains(CharSequence) in the type String is not applicable for the 
arguments (char)

I don't know why it says charsequence when I just used a simple array. The purpose of this part of a code is like a checker for invalid inputs. Here is the code:

                for(int i = 0; i <= 9; i++) {
                    if(GN.contains(Integer.toString(i))){
                        checked = false;
                        if(!checked) {
                            System.out.println("Invalid type, try again.");
                            main.GivenName();
                        } else {
                            String InvalidSym = "`!@#$%^&*()_=+{}[]|\";:\\?";
                            char[] FinalCheck = new char[InvalidSym.length()];
                            for(int j = 0; j <= FinalCheck.length; j++) {
                                  FinalCheck[j] = InvalidSym.charAt(j);
                            }
                            for(int k = 0; k <= FinalCheck.length; k++) {
                                if(GN.contains(FinalCheck[k])) {
                                    checked = false;
                                }
                            }
                        }
                    }
                } //second checker

Answer 1

FinalCheck is a char array which doesn't implemented CharSequence interface

so you can try

if(GN.contains(String.valueOf(FinalCheck[k])))

or you can convert GN into char array once and write a method to check if FinalCheck[k] is in GN array

Answer 2

contains methods is not applicable for char value, the last for loop should contains this if statement:

  for(int k = 0; k <= FinalCheck.length; k++) {
     if(GN.contains(String.valueOf(FinalCheck[k]))) {
         checked = false;
      }
  }

on your code the FinalCheck[k] is a char value as the type of the FinalCheck array is char[]. using the valueOf will convert this char value to String value.