compare first n symbols

package ch.fhnw.claudemartin;

import java.util.Arrays;

public class SomeClass {
  public static void main(final String[] args) {
    test("", "", true);
    test("12345", "12345", true);
    test("abcdefg", "abcdefg", true);
    test("abcdeXX", "abcdeYY", true);
    test("xzy", "abc", false);
    test("xzy", "abcde", false);
    test("a", "A", false);
    test("12345", "12345X", true);

    // one symbol in two chars (surrogate pair):
    String clef = "\uD834\uDD1E";
    clef = clef + clef + clef + clef + clef + clef;
    test(clef, clef + clef, true);

    // Combination with diacritical mark (acute):
    // this might have to fail. requirements unclear.
    test("é", "e\u0301", true);
  }

  static void test(final String a, final String b, final boolean expected) {
    final boolean actual = equalFirst5(a, b);
    (actual == expected ? System.out : System.err)
        .format("'%s' / '%s' = %s%n", a, b, actual);
  }

  public static boolean equalFirst5(final String a, final String b) {
    return equalFirstN(a, b, 5);
  }

  public static boolean equalFirstN(final String a, final String b, final int n) {
    if (a == b)
      return true;
    final int[] ia = a.codePoints().limit(n).toArray();
    final int[] ib = b.codePoints().limit(n).toArray();
    return Arrays.equals(ia, ib);
  }
}