Sorting keyset of java.util.property

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.

Any pointers to solve this issue would be helpful.

Solution

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.