Sorting keyset of java.util.property

Question

for some reason, I'm in a situation where I need to use a property file like:

1=1
2=2
3=3
4=4
5=5
6=6
7=7
12=12
13=13
14=14
15=15
16=16
17=17
23=23
24=24
25=25
26=26
27=27
34=34
35=35
36=36
37=37
45=45
46=46
47=47
56=56
57=57
67=67
123=123
124=124
125=125
126=126
.................
24567=24567
34567=34567
123456=123456
123457=123457
123467=123467
123567=123567
124567=124567
134567=134567
234567=234567
1234567=1234567

And I have utility handler class to sort the keys

public class PropertyHandler {

    private static PropertyHandler instance;
    private Properties properties;

    private PropertyHandler() {
        InputStream fos = null;
        try {
            fos = PropertyHandler.class.getClassLoader().getResourceAsStream("dow-pattern.properties");
            properties = new Properties() {
                @Override
                public Set<Object> keySet() {
                    return Collections.unmodifiableSet(new TreeSet<Object>(super.keySet()));
                }

                @Override
                public synchronized Enumeration<Object> keys() {
                    return Collections.enumeration(new TreeSet<Object>(super.keySet()));
                }
            };
            properties.load(fos);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                fos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    private static PropertyHandler getInstance() {
        if (instance == null) {
            instance = new PropertyHandler();
        }
        return instance;
    }

    private Properties getProperties() {
        return properties;
    }

    public static String getStringProperty(String propertyName) {
        return PropertyHandler.getInstance().getProperties().getProperty(propertyName);
    }

    public static int getIntProperty(String propertyName) {
        return Integer.parseInt(PropertyHandler.getInstance().getProperties().getProperty(propertyName));
    }

    public static Set<Object> getAllKeys() {
        return PropertyHandler.getInstance().getProperties().keySet();
}
}

But when I print the keys, by calling "getAllKeys()" the order of keys as not expected. It is printed in a random fashion.

1
12
123
1234
12345
123456
1234567
123457
12346
123467
12347
1235
12356
123567
12357
1236
........

Any pointers to solve this issue would be helpful.

Answer 1

That's not random, that's sorted alphabetically. You need to sort the values numerically. The easiest way would be converting the Strings to Integers before adding them to the TreeSet.