In java, how to check if a string contains a substring , ( ignoring the case ) ?

Question

I have two Strings: str1 and str2. How to check if str2 is contained within str1, ignoring case?

Answer 1

You can use the toLowerCase() method:

public boolean contains( String haystack, String needle ) {
  haystack = haystack == null ? "" : haystack;
  needle = needle == null ? "" : needle;

  // Works, but is not the best.
  //return haystack.toLowerCase().indexOf( needle.toLowerCase() ) > -1

  return haystack.toLowerCase().contains( needle.toLowerCase() )
}

Then call it using:

if( contains( str1, str2 ) ) {
  System.out.println( "Found " + str2 + " within " + str1 + "." );
}

Notice that by creating your own method, you can reuse it. Then, when someone points out that you should use contains instead of indexOf, you have only a single line of code to change.

Answer 2

str1.toLowerCase().contains(str2.toLowerCase())

Answer 3

I'd use a combination of the contains method and the toupper method that are part of the String class. An example is below:

String string1 = "AAABBBCCC";
String string2 = "DDDEEEFFF";
String searchForThis = "AABB";

System.out.println("Search1="+string1.toUpperCase().contains(searchForThis.toUpperCase()));

System.out.println("Search2="+string2.toUpperCase().contains(searchForThis.toUpperCase()));

This will return:
Search1=true
Search2=false

Answer 4

Well since this is homework if you really want to impress your Professor, use a regex, just look them up a good book is Mastering Regular Expressions by O'Reilly, but it's heavy towards perl, although many of the concepts can apply to most regular expressions.

Answer 5

You can try with the Class Scanner from java.util package