java - 比较具有大量属性的类的两个实例

Question

我有一个类有超过 30 个属性。

我想覆盖 equals 方法以便比较我的类的两个实例。

但是我想避免像这样重写我的方法中的所有 30 个属性

@Override
public boolean equals(java.lang.Object o) {
    if (this == o) {
        return true;
    }
    if (o == null || getClass() != o.getClass()) {
        return false;
    }
    Address address = (Address) o;
    return Objects.equals(this.attr1, address.attr1) &&
            Objects.equals(this.attr2, address.attr2) &&
            Objects.equals(this.attr3, address.attr3) &&
            ......
            Objects.equals(this.attr30, address.attr30);

}

你有更简单妥当的方法吗？

Answer 1

好吧，这基本上是必要的样板代码类型。幸运的是，有很多开发人员和您一样讨厌编写这样的代码。出于这样的原因， Lombok 项目成立了。

请see this link.

例如，请参阅从我上面链接的页面中提取的以下两个代码片段:

Lombok

import lombok.EqualsAndHashCode;

@EqualsAndHashCode(exclude={"id", "shape"})
public class EqualsAndHashCodeExample {
  private transient int transientVar = 10;
  private String name;
  private double score;
  private Shape shape = new Square(5, 10);
  private String[] tags;
  private int id;

  public String getName() {
    return this.name;
  }

  @EqualsAndHashCode(callSuper=true)
  public static class Square extends Shape {
    private final int width, height;

    public Square(int width, int height) {
      this.width = width;
      this.height = height;
    }
  }
}

普通 Java

import java.util.Arrays;

public class EqualsAndHashCodeExample {
  private transient int transientVar = 10;
  private String name;
  private double score;
  private Shape shape = new Square(5, 10);
  private String[] tags;
  private int id;

  public String getName() {
    return this.name;
  }

  @Override public boolean equals(Object o) {
    if (o == this) return true;
    if (!(o instanceof EqualsAndHashCodeExample)) return false;
    EqualsAndHashCodeExample other = (EqualsAndHashCodeExample) o;
    if (!other.canEqual((Object)this)) return false;
    if (this.getName() == null ? other.getName() != null : !this.getName().equals(other.getName())) return false;
    if (Double.compare(this.score, other.score) != 0) return false;
    if (!Arrays.deepEquals(this.tags, other.tags)) return false;
    return true;
  }

  @Override public int hashCode() {
    final int PRIME = 59;
    int result = 1;
    final long temp1 = Double.doubleToLongBits(this.score);
    result = (result*PRIME) + (this.name == null ? 43 : this.name.hashCode());
    result = (result*PRIME) + (int)(temp1 ^ (temp1 >>> 32));
    result = (result*PRIME) + Arrays.deepHashCode(this.tags);
    return result;
  }

  protected boolean canEqual(Object other) {
    return other instanceof EqualsAndHashCodeExample;
  }

  public static class Square extends Shape {
    private final int width, height;

    public Square(int width, int height) {
      this.width = width;
      this.height = height;
    }

    @Override public boolean equals(Object o) {
      if (o == this) return true;
      if (!(o instanceof Square)) return false;
      Square other = (Square) o;
      if (!other.canEqual((Object)this)) return false;
      if (!super.equals(o)) return false;
      if (this.width != other.width) return false;
      if (this.height != other.height) return false;
      return true;
    }

    @Override public int hashCode() {
      final int PRIME = 59;
      int result = 1;
      result = (result*PRIME) + super.hashCode();
      result = (result*PRIME) + this.width;
      result = (result*PRIME) + this.height;
      return result;
    }

    protected boolean canEqual(Object other) {
      return other instanceof Square;
    }
  }
}

如果您喜欢这种方法，我建议您完整地查看 Project Lombok。它确实有助于清理您的代码!

<强>!!!当心!!!为了能够实际使用 Lombok 生成的方法，您需要将 Lombok 插件安装到您的 IDE 中!否则，您的 IDE 将不知道自动生成的方法。