Course Module 3. Java Professional - Lecture: apache-commons-lang library

Complicated equals() method

To easily implement the equals method , you can use the EqualsBuilder class . Here are some examples to show how it works.

Setting specific fields for comparison:

public class User {
   private String name;
   private String email;

   @Override
   public boolean equals(Object o) {
       if (this == o) return true;

       if (!(o instanceof User user)) return false;

       return new EqualsBuilder().append(name, user.name).append(email, user.email).isEquals();
   }
}

Also, this class can compare objects through reflection:

@Override
public boolean equals(Object obj) {
   return EqualsBuilder.reflectionEquals(this, obj);
}

Complicated hashCode() method

To implement the hashCode method , you must use the HashCodeBuilder class .

Field selection:

@Override
public int hashCode() {
   return new HashCodeBuilder(17, 37)
           .append(name)
           .append(email)
           .toHashCode();
}

Using reflection to build hash code:

@Override
public int hashCode() {
   return HashCodeBuilder.reflectionHashCode(this);
}

We use reflection and ignore certain fields:
@Override
public int hashCode() {
   return HashCodeBuilder.reflectionHashCode(this, "name");
}

Complicated toString() method

In a similar way, you can even implement the toString() method . Again, we use the ToStringBuilder class .

The fields are set as in the previous two cases:

@Override
public String toString() {
   return new ToStringBuilder(this)
           .append(name)
           .append(email)
           .toString();
}

Result example:

org.example.User@4b67cf4d[name=John,email=email@email.com]

You can also specify field names explicitly:

@Override
public String toString() {
   return new ToStringBuilder(this)
           .append("nameUser", name)
           .append("emailUser", email)
           .toString();
}

Result example:

org.example.User@4b67cf4d[nameUser=John,emailUser=email@email.com]

You can change the text style using the settings:

@Override
public String toString() {
   return new ToStringBuilder(this, ToStringStyle.SHORT_PREFIX_STYLE)
           .append(name)
           .append(email)
           .toString();
}

Result example:

User[John,emailUser=email@email.com]

There are several styles like JSON, no Classname, short and others.

Using reflection:

@Override
public String toString() {
   return ToStringBuilder.reflectionToString(this);
}

Using reflection and specifying a specific style:

@Override
public String toString() {
   return ToStringBuilder.reflectionToString(this, ToStringStyle.SHORT_PREFIX_STYLE);
}