JPoint 2018を使用したOdnoklassnikiのタスクの代替ルック

1.音楽トラックの分割と分割

/** * @return partition between 0 inclusive * and partitions exclusive */ int partition(Track track, int partitions) { assert track != null; assert partitions > 0; return track.hashCode() % partitions; } 

サーバー上のTrackオブジェクトをパーティション分割するアルゴリズムの何が問題になっていますか？

hashCode（）

同じオブジェクトで複数回呼び出されたとき
Javaアプリケーションの実行、 hashCodeメソッド
情報がない場合は、常に同じ整数を返す必要があります
オブジェクトの等equals比較で使用されるオブジェクトが変更されます。
この整数は、1回の実行で一貫性を保つ必要はありません。
同じアプリケーションの別の実行へのアプリケーション。

 public class Address { private final String street; private final Integer house; } 

  @Override public int hashCode() { int result = street != null ? street.hashCode() : 0; result = 31 * result + (house != null ? house.hashCode() : 0); return result; } 

 public final class String { /** * Returns a hash code for this string. The hash code for a * {@code String} object is computed as * <blockquote><pre> * s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1] * </pre></blockquote> * using {@code int} arithmetic, where {@code s[i]} is the * <i>i</i>th character of the string, {@code n} is the length of * the string, and {@code ^} indicates exponentiation. * (The hash value of the empty string is zero.) * * @return a hash code value for this object. */ @Override public int hashCode() { int h = hash; if (h == 0 && value.length > 0) { char val[] = value; for (int i = 0; i < value.length; i++) { h = 31 * h + val[i]; } hash = h; } return h; } } public final class Integer { /** * Returns a hash code for this {@code Integer}. * * @return a hash code value for this object, equal to the * primitive {@code int} value represented by this * {@code Integer} object. */ @Override public int hashCode() { return Integer.hashCode(value); } /** * Returns a hash code for a {@code int} value; compatible with * {@code Integer.hashCode()}. * * @param value the value to hash * @since 1.8 * * @return a hash code value for a {@code int} value. */ public static int hashCode(int value) { return value; } } 

  switch(s) { case "s": System.out.println("S"); break; case "b": System.out.println("B"); break; } 

  int var_ = -1; switch(s.hashCode()) { case 98: if(s.equals("b")) { var_ = 1; } break; case 115: if(s.equals("s")) { var_ = 0; } } switch(var_) { case 0: System.out.println("S"); break; case 1: System.out.println("B"); } 

断言する

 public class Main { public static void main(String[] args) { assert args.length != 0; assert args.length == 0; System.out.println("OMG! Is it possible?"); } } 

assertを使用しない理由

 /** * An {@code Error} is a subclass of {@code Throwable} * that indicates serious problems that a reasonable application * should not try to catch. Most such errors are abnormal conditions. * The {@code ThreadDeath} error, though a "normal" condition, * is also a subclass of {@code Error} because most applications * should not try to catch it. * <p> * A method is not required to declare in its {@code throws} * clause any subclasses of {@code Error} that might be thrown * during the execution of the method but not caught, since these * errors are abnormal conditions that should never occur. * * That is, {@code Error} and its subclasses are regarded as unchecked * exceptions for the purposes of compile-time checking of exceptions. * * @author Frank Yellin * @see java.lang.ThreadDeath * @jls 11.2 Compile-Time Checking of Exceptions * @since JDK1.0 */ public class Error extends Throwable { /* code omitted */ } 

Errorは、合理的なアプリケーションがキャッチしようとしてはならない重大な問題を示します。 そのようなエラーのほとんどは異常な状態です。

おわりに