normalize() unconditionally called decomposeHangul() and composeHangul() — both O(n) passes — even for strings with no Hangul content (0xAC00–0xD7A3). This penalizes all non-ASCII normalization (Greek, Arabic, CJK, etc.).

Changes

• Single-pass Hangul detection: the existing scan loop now also checks for Hangul syllables. Sets hasHangul = true and breaks early on first match; otherwise continues scanning so a Hangul character appearing later in the string isn't missed.
• Conditional Hangul processing: decomposeHangul() and composeHangul() are now gated on hasHangul.

// Before
if (needsNormalizing) {
    s = decomposeHangul(s);           // always called
    UnicodeString ustring = new UnicodeString(s);
    String result = ustring.decompose().compose().toString();
    result = composeHangul(result);   // always called
    return result;
}

// After
if (needsNormalizing) {
    if (hasHangul) s = decomposeHangul(s);
    UnicodeString ustring = new UnicodeString(s);
    String result = ustring.decompose().compose().toString();
    if (hasHangul) result = composeHangul(result);
    return result;
}