Java – collection removeAll ignore case?

OK, that's my problem I have to use HashSet. I use the removeAll method to delete existing values from another collection

Before calling this method, I explicitly add values to the collection Before adding, I call on each string Touppercase(), because the values in the two lists are different There is no rhythm or reason

Once I call removeAll, I need to return the original case to the value left in set Is there a valid method without running the original list and using comparetoignorecase?

Example:

List 1:

"BOB"
"Joe"
"john"
"MARK"
"dave"
"Bill"

Listing 2:

"JOE"
"MARK"
"DAVE"

Then, use touppercase () on strings to create a separate HashSet for each list Then call removeAll..

Set1.removeAll(set2);

Set1:
    "BOB"
    "JOHN"
    "BILL"

I need to re list this list:

"BOB"
"john"
"Bill"

Any ideas would be appreciated I know it's bad. There should be a standard original list, but it's not my decision

Solution

In my original answer, I inadvertently suggested using the comparator, but this will cause TreeSet to violate the equals contract and is an error waiting to occur:

// Don't do this:
Set<String> setA = new TreeSet<String>(String.CASE_INSENSITIVE_ORDER);
setA.add("hello");
setA.add("Hello");
System.out.println(setA);

Set<String> setB = new HashSet<String>();
setB.add("HELLO");
// Bad code; violates symmetry requirement
System.out.println(setB.equals(setA) == setA.equals(setB));

It is best to use a dedicated type:

public final class CaselessString {
  private final String string;
  private final String normalized;

  private CaselessString(String string,Locale locale) {
    this.string = string;
    normalized = string.toUpperCase(locale);
  }

  @Override public String toString() { return string; }

  @Override public int hashCode() { return normalized.hashCode(); }

  @Override public boolean equals(Object obj) {
    if (obj instanceof CaselessString) {
      return ((CaselessString) obj).normalized.equals(normalized);
    }
    return false;
  }

  public static CaselessString as(String s,Locale locale) {
    return new CaselessString(s,locale);
  }

  public static CaselessString as(String s) {
    return as(s,Locale.ENGLISH);
  }

  // TODO: probably best to implement CharSequence for convenience
}

This code is unlikely to cause an error:

Set<CaselessString> set1 = new HashSet<CaselessString>();
set1.add(CaselessString.as("Hello"));
set1.add(CaselessString.as("HELLO"));

Set<CaselessString> set2 = new HashSet<CaselessString>();
set2.add(CaselessString.as("hello"));

System.out.println("1: " + set1);
System.out.println("2: " + set2);
System.out.println("equals: " + set1.equals(set2));

Unfortunately, this is more lengthy