@Data 注解

@Data注解，主要做的工作如下
1、添加equals，CanEqual 方法，添加hashCode方法
2、添加toString方法
3、添加Set方法
4、添加Get方法
而上面的四件事，lombok中，有分别的注解去做，分别是 @EqualsAndHashCode、@ToString、@Setter、@Getter
所以，如果单纯为了添加Get、set 方法而使用data，会导致添加了1、2步骤中的冗余代码

这是使用Data注解的类

package com;

import lombok.Data;

@Data
public class Teacher {

  private int id;
}

如果不加Data注解，编译之后的文件长这样

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package com;

public class Teacher {
  private int id;

  public Teacher() {
  }
}

加上Data注解之后，长下面这样

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package com;

public class Teacher {
  private int id;

  public Teacher() {
  }

  public int getId() {
    return this.id;
  }

  public void setId(int id) {
    this.id = id;
  }

  public boolean equals(Object o) {
    if (o == this) {
      return true;
    } else if (!(o instanceof Teacher)) {
      return false;
    } else {
      Teacher other = (Teacher)o;
      if (!other.canEqual(this)) {
        return false;
      } else {
        return this.getId() == other.getId();
      }
    }
  }

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

  public int hashCode() {
    int PRIME = true;
    int result = 1;
    int result = result * 59 + this.getId();
    return result;
  }

  public String toString() {
    return "Teacher(id=" + this.getId() + ")";
  }
}

如果将@Data注解换成@Setter注解，编译之后的代码会变成下面这个样子

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package com;

public class Teacher {
  private int id;

  public Teacher() {
  }

  public void setId(int id) {
    this.id = id;
  }
}