Shortest way to reverse Properties

Question

In Java I have a java.util.Properties object and I want to obtain another one with the same pairs but keys converted to values and viceversa.

If there are c

Answer 1

You can consider using a BiMap by google collections which is essentially a reversable Map. It guarantees uniquness of keys as well as values.

Check it out here. This is the API

Answer 2

Something like:

Properties fowards = new Properties();
fowards.load(new FileInputStream("local.properties"));

Properties backwards = new Properties();

for (String propertyName : fowards.stringPropertyNames())
{
  backwards.setProperty(forwards.get(propertyName), propertyName);
}

Answer 3

A Properties object is a Hashtable object, so you should be able to do something like:

Hashtable<String, String> reversedProps = new Hashtable<String, String>();

for (String key : props.keySet()) {
    reversedProps.put(props.get(key), key);
}

Result: 3 lines of code.

This code is untested, but it should give you the idea.