java - 如何解决[线程“main”java.lang.NullPointerException中的异常]的问题

Question

所以我刚开始学习Java，我就面临这个问题。我的主要是试图调用该方法getOperator，但它给了我[Exception in thread "main" java.lang.NullPointerException]错误。我该如何解决？

    //get operator +, - or *
    public static char getOperator() 
    {
        //set operator as random to return different types
        //of operators from cases 0 to 2

        int oper =  rand.nextInt(3);// **error occurs on this line**


        switch (oper)
        {
            case 0: return '+'; //return as + if case is 0
            case 1: return '-'; //return as - if case is 1
            case 2: return '*'; //return as * if case is 2
            default: return '+'; //default will return as +
        }
    }

标签： javanullpointerexception

Answer 1

    int oper =  rand.nextInt(3);// **error occurs on this line**

这几乎肯定意味着rand是null。您需要为rand. 也许是这样的：

private static final Random rand = new SecureRandom();