Java，嵌套类: how to access 'higher' level variable

Question

运行此代码时出现错误!

   private class ValuesClass {

            List<Float> value;

            public void addv(String _value) {
                    Float f = new Float(_value);
                    this.value.add(f);
            }
    }

这是返回的错误

0.83
0.83
Exception in thread "main" java.lang.NullPointerException
    at com.gsware.gsmarketanalyzer.StockQuote$ValuesClass.addv(StockQuote.java:216)

不知道哪里出错了!

Answer 1

您必须实例化该列表，否则value为空:

List<Float> value = new ArrayList<Float>;