Parsing a string and printing string literals to screen

I am trying to print any string literals I have in a file I am reading using a scan method. I am limited to follow a guide as to the structure of my programme, by my professor.

Currently, I have this section of code that is printing string literals, or is trying to:

public static void scan (String prog) {
    
            int n = prog.length();
            int index = 0;
            int lineNumber = 1;
            
            
            
            while (index < n) {
                
                char ch = prog.charAt(index);
                
                
                
                boolean whiteSpace = isWhiteSpace(ch);
                boolean newLine = isLineBreak(ch);
                TokenType sym = getSymbol(ch);
                TokenType op = getOp(ch);
                boolean letter = isLetter(ch);
                boolean digit = isDigit(ch);
                
                // start of if statement preceding this point               
            
                else if (ch == '\"') {
                    String str = "";
                    str += ch;
                    
                    index++;
                    
                        while (index < n) {
                            
                            ch = prog.charAt(index);
                            
                                if (ch != '\"') {
                            
                                    str += ch;
                                    index++;
                                    }
                                else break; 
                            }
                        
                        System.out.println(lineNumber + "," + TokenType.STRING + ", " + str);
                        index++;
                        continue;           
                }
                else {
                    System.out.println("Encountered something not expected: " + ch);
                    index++;
                    continue;
                } 
                
        

This outputs the first " and all the characters before the next " but not the last " of the string literal itself. How can I go about changing this code to print the whole string literal?

Current output:

11, STRING, "This just random code

What I need:

11, STRING, "This just random code"