Noah Thomas Gary Noah Thomas Gary - 3 months ago 29
Java Question

Java ArrayList Contains() method not working

I have no doubt that the contains() method is working correctly but apparently I am doing something wrong. I am working on an android app and I am detecting WiFi and listing the WiFi in a listView. I am attempting to filter out duplicate occurrences of the same Access Point so I am creating an array to keep track of duplicates. Here is my code:

public void getWifi(){

ListView wifiList = (ListView)findViewById(R.id.listView);

WifiManager wifiManager = (WifiManager) getSystemService(Context.WIFI_SERVICE);
List<ScanResult> apList = wifiManager.getScanResults();
wifiManager.startScan();

List<String> wifees = new ArrayList<>();

//split info into arrays
for(int i=0; i < apList.size(); i++){

String[] daList = String.valueOf(apList.get(i)).split(",");

String info = "";
List<String> SSIDs = new ArrayList<>();

for (String listItem : daList) {
String topic = String.valueOf(listItem.split(":")[0]);
String val = listItem.split(":")[1];
Log.d(TAG, topic);
if (Objects.equals(topic, "SSID")) {
if(SSIDs.contains(val)){
Log.d(TAG, "CONTAINS");
break;
} else {
SSIDs.add(val);
info = val;
}
} else if (Objects.equals(topic, " level")){
String strength = "";
if (Integer.parseInt(val.substring(1)) >= -35) {
strength = "100%";
} else if (Integer.parseInt(val.substring(1)) <= -35 && Integer.parseInt(val.substring(1)) >= -65) {
strength = "50%";
} else {
strength = "1%";
}
info += " " + strength;
}
}
wifees.add(info);
}

assert wifiList != null;
ArrayAdapter apter = new ArrayAdapter(this, android.R.layout.simple_list_item_1, wifees);
wifiList.setAdapter(apter);
}


This is the contents of an apList item or what I get when I call apList.get(i):

SSID: SCHOOL-GUEST, BSSID: 04:04:04:04:04:04, capabilities: [ESS], level: -91, frequency: 2412, timestamp: 72500687089, distance: ?(cm), distanceSd: ?(cm), passpoint: no, ChannelBandwidth: 0, centerFreq0: 0, centerFreq1: 0, 80211mcResponder: is not supported


Here is the output of that code(roughly because it is on a phone and I would rather not include the AP names for security reasons):

SCHOOL-WIRELESS 100%
SCHOOL-SECURE 50%
SCHOOL-GUEST 50%
SCHOOL WIRELESS 1%
SCHOOL_WIRELESS 1%
SCHOOL-SECURE 1%
SCHOOL-GUEST 1%
bxz1872 50%
...
...
...
(so on and so forth)


If I could just get a second opinion that would be great. I feel like I am missing something obvious. Thanks!

Answer

.contains doesnt work, because you call List<String> SSIDs = new ArrayList<>(); within for(int i=0; i < apList.size(); i++){. You basically create new empty List for every loop-iteration. You should call it once befor the outer for-loop:

List<String> SSIDs = new ArrayList<>();
for(int i=0; i < apList.size(); i++){
    ...
}