ArrayList问题并没有出现值

Question

我有一个arrayList的问题.这是我的arrayList代码

我知道我的arrayList方法有一些问题,但我无法发现它.

arrayList的方法

public ArrayList<Tour> countryList(String country)
    {
        ArrayList<Tour> newList = null;
        switch (country)
        {
        case "Indonesia":
            country = "IN";
            break;
        case "Thailand":
            country = "TH";
            break;
        case "Singapore":
            country = "SI";
            break;
        case "Brunei":
            country = "BR";
            break;
        case "Philipines":
            country = "PH";
            break;
        case "Vietnam":
            country = "VI";
            break;
        case "Laos":
            country = "LA";
            break;
        case "Myammmar":
            country = "MY";
            break;
        case "Malaysia":
            country = "MS";
            break;
        }
        if(TList.indexOf(country)!= 1)
        {
            return newList;
        }

        return newList;

    }

在主要班级

private static void displayAllToursCountry()
    {
        System.out.print("Please enter the name of the country: ");
        String country = sc.next();

        while (country == "")
        {
            System.out.print("Please enter a valid country name: ");
            country = sc.next();
        }
        System.out.println("Country:" + country);
        System.out.println(ta1.countryList(country));
    }

为什么没有价值出来？我做错了什么地方？谢谢

Answer 1

你没有把任何东西放到ArrayList中.

你刚刚做的

ArrayList<Tour> newList = null;

然后 return newList;

它甚至没有初始化.

你应该初始化它:ArrayList<Tour> newList = new ArrayList<>() 然后把一些元素放入:newList.add(myTour);