java只能使用getter方法一次

Question

我正在从事一个Java项目，在该项目中，我在TextAnalyzer类中使用了下面的getter方法：

public Hashtable<String, Double> getTotalFeatureOccurances() {
    return(feat_occur_total);
}//getTotalFeatureOccurances

我还有private class变量：

private Hashtable<String, Double> feat_occur_total;

我使用getter，向散列添加更多术语，然后想再次获取散列，但它总是返回空。更糟糕的是，如果我不从哈希中添加或删除任何内容，但执行两次get，我仍然会收到并在第二次清空哈希

以下是我的主要代码：

TextAnalyzer ta = new TextAnalyzer();
        feat_occur_cat = ta.wordOccurancesCount(text, features);
        feat_occur_total = ta.getTotalFeatureOccurances();

        Enumeration<Double> e = feat_occur_total.elements();
        while(e.hasMoreElements()) {
            System.out.println(e.nextElement());
        }//while

        feat_occur_total.clear();
        feat_occur_total  = ta.getTotalFeatureOccurances();

        e = feat_occur_total.elements();
        System.out.println("\n\nSECOND GET\n\n");
        while(e.hasMoreElements()) {
            System.out.println(e.nextElement());
        }//while

我得到了输出：

2.0
1.0
5.0
1.0
1.0
3.0
2.0
3.0


SECOND GET

下面是全班同学：

public class TextAnalyzer {

    TextAnalyzer() {
        this.feat_occur_total = new Hashtable<String, Double>();
    }

    public String[][] wordOccurancesCount(String text, Vector<String> features) {
        String[][] occur = new String[features.size()][features.size()];

        for(int ndx=0; ndx<features.size(); ndx++) {
            int count=0;

            Pattern p = Pattern.compile("(?:^|\\s+|\\()\\s*(" + features.elementAt(ndx).trim() + ")\\w*(?:,|\\.|\\)|\\s|$)", Pattern.CASE_INSENSITIVE | Pattern.MULTILINE | Pattern.CANON_EQ);
            Matcher m = p.matcher(text);
            m.usePattern(p);

            while(m.find())
                count++;

            occur[ndx][0] = features.elementAt(ndx);
            occur[ndx][1] = String.valueOf(count);

            if(this.feat_occur_total.containsKey(features.elementAt(ndx))) {
                double temp = this.feat_occur_total.get(features.elementAt(ndx));
                temp += count;
                this.feat_occur_total.put(features.elementAt(ndx), temp);
            }//if
            else {
                this.feat_occur_total.put(features.elementAt(ndx), Double.valueOf(count));
            }//else
        }//for

        return(occur);
    }//word

    public Hashtable<String, Double> getTotalFeatureOccurances() {
        return(feat_occur_total);
    }//getTotalFeatureOccurances

    private Hashtable<String, Double> feat_occur_total;

}//TextAnalyzer