Proxy Set In Java

I'm using proxy to crawl some data. So, for now I've this snippet,

public static void IPchange() {
String proxy = 121.11.23.21;
String port = 8080;
Properties systemProperties = System.getProperties();
systemProperties.put("proxySet", "true");
systemProperties.setProperty("http.proxyHost", proxy);
systemProperties.setProperty("http.proxyPort", port);
}

Now, I've a thread say T which is calls this IPchange() method to use proxy. Now, Thread T creates other threads say T1, T2. When I give URL to crawl for this T1 and T2. T1 and T2 will not call IPchange() method. To crawl URL, T1 and T2 now using my Original IP?