String contains - ignore case

You can use

org.apache.commons.lang3.StringUtils.containsIgnoreCase(CharSequence str,
                                     CharSequence searchStr);

Checks if CharSequence contains a search CharSequence irrespective of case, handling null. Case-insensitivity is defined as by String.equalsIgnoreCase(String).

A null CharSequence will return false.

This one will be better than regex as regex is always expensive in terms of performance.

For official doc, refer to : StringUtils.containsIgnoreCase

Update :

If you are among the ones who

• don't want to use Apache commons library
• don't want to go with the expensive regex/Pattern based solutions,
• don't want to create additional string object by using toLowerCase,

you can implement your own custom containsIgnoreCase using java.lang.String.regionMatches

public boolean regionMatches(boolean ignoreCase,
                             int toffset,
                             String other,
                             int ooffset,
                             int len)

ignoreCase : if true, ignores case when comparing characters.

public static boolean containsIgnoreCase(String str, String searchStr)     {
    if(str == null || searchStr == null) return false;

    final int length = searchStr.length();
    if (length == 0)
        return true;

    for (int i = str.length() - length; i >= 0; i--) {
        if (str.regionMatches(true, i, searchStr, 0, length))
            return true;
    }
    return false;
}

If you won't go with regex:

"ABCDEFGHIJKLMNOP".toLowerCase().contains("gHi".toLowerCase())

You can use java.util.regex.Pattern with the CASE_INSENSITIVE flag for case insensitive matching:

Pattern.compile(Pattern.quote(strptrn), Pattern.CASE_INSENSITIVE).matcher(str1).find();

Try this

public static void main(String[] args)
{

    String original = "ABCDEFGHIJKLMNOPQ";
    String tobeChecked = "GHi";

    System.out.println(containsString(original, tobeChecked, true));        
    System.out.println(containsString(original, tobeChecked, false));

}

public static boolean containsString(String original, String tobeChecked, boolean caseSensitive)
{
    if (caseSensitive)
    {
        return original.contains(tobeChecked);

    }
    else
    {
        return original.toLowerCase().contains(tobeChecked.toLowerCase());
    }

}