LinkedHashSet.contains() returns true when it should return false

Question

public class MyClass extends Activity {
    public static final String DEFAULT_ID = "def";
    public static final LinkedHashSet<String> DEF_IDS = new LinkedHashSet<>(Arrays.asList(DEFAULT_ID));

    private boolean isDefault(String currentId) {
        Log.v(TAG,"isdefault("+currentId+") = " + DEF_IDS.contains(currentId));
        return DEF_IDS.contains(currentId);
    }
}

In log:

isdefault(profile0) = true

WTF? If DEF_IDS doesn't contain "profile0", why does it says that it contains?

This means someone put it here before calling `isDefault()`. The reason is likely that `DEF_IDS` is static and shared among classes. — Alex Salauyou, Aug 20 '15 at 12:40
I just tested your code and [it works as expected](https://ideone.com/zszk17). Something else must be wrong. — Tunaki, Aug 20 '15 at 12:40
@dotvav there's no variable profile 0. I was just to lazy to write "isdefault(\""+currentId+"\") = " — kandi, Aug 20 '15 at 12:41
DEF_IDS aren't used anywhere but in this method. There are no classes extend MyClass — kandi, Aug 20 '15 at 12:43
1) Add printing full contents of DEF_IDS to `isDefault()` method. 2) Try using immutable set to guarantee that noone can change its contents. — Deinlandel, Aug 20 '15 at 12:44
@danpetruk `isDefault()` definetly should be static, because it uses only static properties. — Alex Salauyou, Aug 20 '15 at 12:44
@SashaSalauyou yes, I agree. But that doesn't slove the problem — kandi, Aug 20 '15 at 12:47
@danpetruk Okay, then just try to `Log.v(TAG, DEF_IDS)` before returning — Alex Salauyou, Aug 20 '15 at 12:49

score 0 · Answer 1 · answered Aug 20 '15 at 12:48

The fault is not in the code you posted. The following produces the expected result.

public static final String DEFAULT_ID = "def";
public static final LinkedHashSet<String> DEF_IDS = new LinkedHashSet<>(Arrays.asList(DEFAULT_ID));

private static boolean isDefault(String currentId) {
    return DEF_IDS.contains(currentId);
}

private void test(String def) {
    System.out.println("isDefault(" + def + ") = " + isDefault(def));
}

public void test() {
    test("def");
    test(DEFAULT_ID);
    test("NOT");
}

by printing

isDefault(def) = true
isDefault(def) = true
isDefault(NOT) = false

score 0 · Answer 2 · answered Aug 20 '15 at 12:49

Executed the code below and it gave me the correct result.
Problem seems to be that your using static LinkedHashSet and it will retain previous values untill you'll not explicitly clear it i.e. initialized only once.

Add more details or close your question as it is not at all clear and don't provide the complete context on how exactly you are using this code.

  public static final String DEFAULT_ID = "def";
            public static final LinkedHashSet<String> DEF_IDS = new LinkedHashSet<>(Arrays.asList(DEFAULT_ID));


        public static void main(String[] args){
            isDefault("profile0");
        } 
            private static boolean isDefault(String currentId) {
               System.out.println("isdefault("+currentId+") = " + DEF_IDS.contains(currentId));
                return DEF_IDS.contains(currentId);
            }

Output:- isdefault(profile0) = false

LinkedHashSet.contains() returns true when it should return false

2 Answers2