ArrayList contains case sensitivity

Question

I am currently using the contains method belonging to the ArrayList class for making a search. Is there a way to make this search case insensitive in java? I found that in C

Answer 1

I would make it like so:

public boolean isStringInList(final List<String> myList, final String stringToFind) {
    return myList.stream().anyMatch(s -> s.equalsIgnoreCase(stringToFind));
}  

Answer 2

Looking at the Java API, there is no such method for contains.

But you could do at least two things:

1. Override the equals method in your ArrayList object with your own, or equalsIgnoreCase(str)

2. Write your own contains method, which should iterate through your ArrayList entities, and do a manual check.

   ArrayList<String> list = new ArrayList<String>();
   ...
   containsIgnoreCase("a", list);
   
   public boolean containsIgnoreCase(String str, ArrayList<String> list){
       for(String i : list){
           if(i.equalsIgnoreCase(str))
               return true;
       }
       return false;
   }
   

Answer 3

The contains method is based on what the equals method of the objects stored in your ArrayList returns. So yes it is possible if you use objects where equals uses a case insensitive comparison.

So you could for example use a class like this (code might still contain some typos)

public class CaseInsensitiveString{
  private final String contents;

  public CaseInsensitiveString( String contents){ this.contents = contents; }

  public boolean equals( Object o ){
    return o != null && o.getClass() == getClass() && o.contents.equalsIgnoreCase( contents);
  }

  public int hashCode(){
    return o.toUpperCase().hashCode();
  }
}

Answer 4

For java8

list.stream().anyMatch(s -> s.equalsIgnoreCase(yourString))

For < java8

• as suggested by Aaron J Lang above
• Or if you know case of your list ( all upper /all lower ) then convert the search string to appropriate case before comparing

Answer 5

Don't reinvent the wheel. Use well tested APIs. For your purpose use Apache Commons StringUtils.

From the Javadoc: Compares given string to a CharSequences vararg of searchStrings returning true if the string is equal to any of the searchStrings, ignoring case.

import org.apache.commons.lang3.StringUtils;
...
StringUtils.equalsAnyIgnoreCase(null, (CharSequence[]) null) = false
StringUtils.equalsAnyIgnoreCase(null, null, null)    = true
StringUtils.equalsAnyIgnoreCase(null, "abc", "def")  = false
StringUtils.equalsAnyIgnoreCase("abc", null, "def")  = false
StringUtils.equalsAnyIgnoreCase("abc", "abc", "def") = true
StringUtils.equalsAnyIgnoreCase("abc", "ABC", "DEF") = true

Answer 6

If you're using Java 8, try:

List<String> list = ...;
String searchStr = ...;
boolean containsSearchStr = list.stream().filter(s -> s.equalsIgnoreCase(searchStr)).findFirst().isPresent();