// list是有重复元素的ArrayList
  HashSet hSet =  new HashSet(list);
  list.clear();
  list.addAll(hSet);

NetWork nw1 = new NetWork();
nw1.id = 1;
nw1.destip = "192.168.1.3";

NetWork nw2 = new NetWork();
nw2.id = 2;
nw2.destip = "192.168.1.5";

NetWork nw3 = new NetWork();
nw3.id = 3;
nw3.destip = "192.168.1.3";

NetWork nw4 = new NetWork();
nw4.id = 4;
nw4.destip = "192.168.1.4";

NetWork nw5 = new NetWork();
nw5.id = 5;
nw5.destip = "192.168.1.3";

mList.add(nw1);
mList.add(nw2);
mList.add(nw3);
mList.add(nw4);
mList.add(nw5);

for (int i = 0; i < mList.size()-1; i++) {
for (int j = mList.size()-1; j > i; j--) {
 if (mList.get(j).destip.equals(mList.get(i).destip)) {
mList.remove(j);
 }
  }
 }