尝试在JSF页面中显示List <String>时出现java.lang.NullPointerException

Question

当我尝试在JSF页面中显示Java List<String>国家时,我在JSF页面中遇到了非常奇怪的问题.这是代码:

 private List<String> listCountries;

    // Get the list with Countries
    public List<String> getlistCountries() { 
        // Generate List of Countries
        initlistCountries();
        return listCountries;
    }

    public void initlistCountries(){
        listCountries.add("Afghanistan");
        listCountries.add("Albania");
        listCountries.add("Algeria");
        listCountries.add("Andorra");
        listCountries.add("Angola");
        ......
    }

这段代码是否正确？我不能使用,@PostConstruct因为我已经使用它了.

加载JSF页面时出现错误:

java.lang.NullPointerException
    at com.DX_57.AC_57.AddAccount.initlistCountries(AddAccount.java:344)
    at com.DX_57.AC_57.AddAccount.getlistCountries(AddAccount.java:339)

Answer 1

你没有初始化listCountries所以做它

 public void initlistCountries(){
        listCountries = new ArrayList<String>();
        listCountries.add("Afghanistan");
        listCountries.add("Albania");
        listCountries.add("Algeria");
        listCountries.add("Andorra");
        listCountries.add("Angola");
        ......
    }