Java SetProperty Not Working

I have a file called config.dedserver and on a JButton click I am editing the values in it using setProperty but it didn't work. It removed everything from the entire file and then added the properties.

This is my code:

String newGems = gem.getText();
String newGold = gold.getText();
String newElixir = elixir.getText();
String newDE = de.getText();
try {
Properties props = new Properties();
props.setProperty("startingGems", newGems);

[Code] ....

And this is what the original file is:

Quote
# Main configuration file for DEDServer

# Starting resource values
startingGold=1000000
startingElixir=1000000
startingDarkElixir=1000000
startingGems=1077

# Saving method. Valid values are:
# -none: database disabled
# -h2: use h2 database (default)
saveMethod=h2

# Save interval (milliseconds)
saveInterval=60000