第 40 条：坚持使用Override注解

坚持使用Override注解.jpeg

错误示例

// Can you spot the bug?
public class Bigram { 
  private final char first; 
  private final char second;
  public Bigram(char first, char second) { 
    this.first = first;
    this.second = second;
  }
  public boolean equals(Bigram b) {
    return b.first == first && b.second == second; 
  }
  public int hashCode() { 
    return 31 * first + second;
  }
  public static void main(String[] args) { 
    Set<Bigram> s = new HashSet<>(); 
    for (int i = 0; i < 10; i++)
      for (char ch = 'a'; ch <= 'z'; ch++) 
        s.add(new Bigram(ch, ch));
    System.out.println(s.size()); 
  }
}

正确示例

public class Bigram { 
  private final char first; 
  private final char second;
  public Bigram(char first, char second) { 
    this.first = first;
    this.second = second;
  }

  @Override
  public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;
    Bigram bigram = (Bigram) o;
    return first == bigram.first &&
            second == bigram.second;
  }

  @Override
  public int hashCode() {
    return Objects.hash(first, second);
  }

  public static void main(String[] args) { 
    Set<Bigram> s = new HashSet<>();
    for (int i = 0; i < 10; i++)
      for (char ch = 'a'; ch <= 'z'; ch++) 
        s.add(new Bigram(ch, ch));
    System.out.println(s.size()); 
  }
}