Whats the purpose of System.setProperties();

Question

Can someone give me a reason why we would use System.setProperties(); if it doesnt affect the actual System Properties for other programs.

Answer 1

I've never done it, but you can use it to fool later calls to System.getProperty() into thinking that those properties were given on the command line.
import java.util.*;
public class Test {
    public static void main(String[] args){
          Properties out = new Properties();
          out.setProperty("com.acme.widget", "bip");
          System.setProperties(out);
          Properties in = System.getProperties();
          for(Object key : in.keySet())
            System.out.println(key + "=" + in.get(key));
}