Check ArrayList contains("") method with equalsIgnoreCase

Question

I have an ArrayList();

List<String> list = new ArrayList<>();
list.add("aaa");
list.add("BBB");
list.add("cCc");
System.out.println(list.contains("aAa"));

Here i want to check contains() method with equalsIgnoreCase method in same line. How can i do it?

`List list = new ArrayList();`, not possible it should be `List list = new ArrayList();` — Prasad Kharkar, Jul 08 '13 at 12:24
@PrasadKharkar I believe `new ArrayList<>()` is also acceptable nowadays. — nanofarad, Jul 08 '13 at 12:25
@Aquillo, Ohh... need to study jdk7 now. Can you please provide some good links for these differences? — Prasad Kharkar, Jul 08 '13 at 12:26
@hexafraction, yeah couldn't know about the jdk7 changes. thanks for that — Prasad Kharkar, Jul 08 '13 at 12:27
@PrasadKharkar http://docs.oracle.com/javase/7/docs/technotes/guides/language/enhancements.html#javase7 — johnchen902, Jul 08 '13 at 12:28
In JDK7, it is `new ArrayList<>();` (this is typed, and avoids redundancy by assuming same type as variable declaration `List list = `) but it is **NOT** `new ArrayList();` (this is still untyped, it compiles with a warning) — ADTC, Jul 08 '13 at 12:30

score 11 · Accepted Answer · answered Jul 08 '13 at 12:25

11

boolean containsEqualsIgnoreCase(Collection<String> c, String s) {
   for (String str : c) {
      if (s.equalsIgnoreCase(str)) {
          return true;
      }
   }
   return false;
}

answered Jul 08 '13 at 12:25

jlordo

37,490
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score 5 · Answer 2 · answered Jul 08 '13 at 12:24

5

You can't. The contract of contains is that it defers to equals. That's a fundamental part of the Collection interface. You have to write a custom method that iterates through the list and checks each value.

answered Jul 08 '13 at 12:24

Thorn G

12,620
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Alexandre Dupriez · Answer 3 · 2013-07-08T13:00:21.290

This is an interesting question from an OO perspective.

One possibility is to transfer the responsibility of the contract you want to enforce (equality without case) to the collected elements themselves, not to the list, with respect to a proper separation of concern.

You would then add a new class for your String objects (without inheritance, String class is final) where you would implement your own hashCode/equals contract.

// Strictly speaking, this is not a String without case, since only
// hashCode/equals methods discard it. For instance, we would have 
// a toString() method which returns the underlying String with the 
// proper case.
public final class StringWithoutCase {
  private final String underlying;

  public StringWithoutCase(String underlying) {
    if (null == underlying)
      throw new IllegalArgumentException("Must provide a non null String");
    this.underlying = underlying;
  }

  // implement here either delegation of responsibility from StringWithoutCase
  // to String, or something like "getString()" otherwise.

  public int hashCode() {
    return underlying.toLowerCase().hashCode();
  }

  public boolean equals(Object other) {
    if (! (other instanceof StringWithoutCase))
      return false;

    return underlying.equalsIgnoreCase(other.underlying);
  }
}

The objects populating the collection would be instances of StringWithoutCase :

Collection<StringWithoutCase> someCollection = ...
someCollection.add(new StringWithoutCase("aaa"));
someCollection.add(new StringWithoutCase("BBB"));
someCollection.add(new StringWithoutCase("cCc"));

Check ArrayList contains("") method with equalsIgnoreCase

3 Answers3