HttpClient中addHeader与setHeader方法有什么不同呢？

addHeader及setHeader方法的功能简介

  
addHeader:
   添加一个新的请求头字段(一个请求头中允许有重名字段)

setHeader:
   设置一个请求头字段
   当出现相同的请求头时,则覆盖以前的值
   否则直接新增头信息 

 
public void testHttpClient(){
	HttpGet httpGet =  new HttpGet();
	httpGet.addHeader("a","java265.com-1");
	httpGet.addHeader("a","java265.com-2");
	httpGet.addHeader("b","java265.com-3");
	httpGet.setHeader("b","java265.com-4");
	httpGet.setHeader("c","java265.com-5");
	Header[] allHeaders = httpGet.getAllHeaders();
	for (Header allHeader : allHeaders) {
		System.out.println(allHeader.getName()+" : "+allHeader.getValue());
	}
	System.out.println("---");
	Header[] as = httpGet.getHeaders("a");
	for (Header a : as) {
		System.out.println(a.getName()+" : " +a.getValue());
	}
	System.out.println("---");
	Header[] bs = httpGet.getHeaders("b");
	for (Header a : bs) {
		System.out.println(a.getName()+" : " +a.getValue());
	}
	System.out.println("---");
	Header a = httpGet.getFirstHeader("a");
	System.out.println(a.getName()+" : " + a.getValue());
	System.out.println("---");
	Header a2 = httpGet.getLastHeader("a");
	System.out.println(a2.getName()+" : " + a2.getValue());
}