CODEWITHSUNDEEP
javaandroid
user3240944
user3240944

Reputation: 331

Set cannot contain duplicates. But it does

the documentation states Set cannot contain duplicates

however this code works fine:

Set<String> vmv = new TreeSet<String>();
vmv.add("a");
vmv.add("a");
System.out.println(vmv.toString());

I just added a duplicate. Can someone explain this.

Upvotes: 2

Views: 120

Answers (2)

&#211;scar L&#243;pez
&#211;scar L&#243;pez

Reputation: 236004

Calling add() twice with the same value won't add it a second time, check the returned boolean and you'll see that the second time it was false, or check the set's size to verify that it didn't change after the second time:

Set<String> vmv = new TreeSet<String>();

System.out.println(vmv.add("a")); // prints true
System.out.println(vmv.size());   // prints 1

System.out.println(vmv.add("a")); // prints false
System.out.println(vmv.size());   // prints 1

Upvotes: 5

Louis Wasserman
Louis Wasserman

Reputation: 198103

From the same page, further down:

The add method adds the specified element to the Set if it's not already present and returns a boolean indicating whether the element was added.

...which is exactly what it's doing. When you print the final set, you should only see one copy of the "duplicate" element.

Upvotes: 2

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