java - 文字列を算術演算に変換する

Question

私は学生に数学のクイズを提示するプログラムを行っています。入力問題の種類を取得し、その文字列を算術演算子に変換する方法を理解するのに苦労しています。コードのその部分のメソッドを次に示します。よろしくお願いします！

public static String getUserChoice(String choice) {
    Scanner in = new Scanner(System.in);

    System.out.println("Please enter the symbol that corresponds to one of the following problems\n"
            + "Addition (+)\n Subtraction (-)\n or Multiplication (*): ");
    choice = in.next();
        if ("+".equals(choice)){
            return +;
        }
        }
    return choice;

更新 私が何をしているのかを理解するのに役立つ場合は、コード全体を次に示します。

    public static void main(String[] args) {
    int digit = 0;
    int random = 0;

    String result1 = getUserChoice("");

    digit = getNumberofDigit1(digit);

    int number1 = getRandomNumber1(digit);
    int number2 = getRandomNumber2(digit);

    System.out.println(number1 + result1 + number2);
    getCorrectAnswer(number1, result1, number2);

}

public static String getUserChoice(String choice) {
    Scanner in = new Scanner(System.in);

    System.out.println("Please enter the symbol that corresponds to one of the following problems\n"
            + "Addition (+)\n Subtraction (-)\n or Multiplication (*): ");
    choice = in.next();


    return choice;
}

public static int getNumberofDigit1(int digit) {
    Scanner in = new Scanner(System.in);

    System.out.println("Enter a 1 for problems with one digit, or a 2 for two-digit problems: ");
    digit = in.nextInt();

    return digit;
}


public static int getRandomNumber1(int numbers) {
        int random = 0;
            if (numbers == 1) {
                random = (int) (1 + Math.random() * 9);
            } else if (numbers == 2) {
                random = (int) (10 + Math.random() * 90);
            }
         return random;   
}

public static int getRandomNumber2(int numbers) {
    int random2 = 0;
            if (numbers == 1) {
                random2 = (int) (1 + Math.random() * 9);
            } else if (numbers == 2) {
                random2 = (int) (10 + Math.random() * 90);
            }
            return random2;
}
public static void getCorrectAnswer(int number1, String result1, int number2) {
}

public static void getUserAnswer() {
    Scanner in = new Scanner(System.in);

}

public static void CheckandDisplayResult() {
}