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Class Names Should Not Shadow Interfaces or Superclasses

Medium
maintainabilityintentionality - clear

What is it?​

This practice addresses the issue of class name shadowing, where a class name is identical to that of its superclass or an interface it implements.

Why apply it?​

Class name shadowing leads to ambiguity, making it unclear which class is being referred to, which can result in potential bugs and reduced code readability.

How to fix it?​

Rename the class to use a more descriptive and unique name that doesn’t conflict with its superclass or implemented interfaces names.

Examples​

Example 1:​

Negative​

The negative example shows a class shadowing the interface it implements, causing ambiguity and potential bugs.

package org.foo.domain;

public interface User {
  void login();
}

package org.foo.presentation;

public class User implements org.foo.domain.User { // Noncompliant
  public void login() {
    System.out.println("Logging in...");
  }
}

Example 2:​

Positive​

The positive example uses unique and descriptive class names that do not conflict with superclasses or implemented interfaces.

package org.foo.domain;

public interface User {
  void login();
}

package org.foo.presentation;

import org.foo.domain.User;

public class UserView implements User { // Compliant
  public void login() {
    System.out.println("Logging in...");
  }
}

Negative​

In this negative example, the class name shadows its superclass, leading to confusion.

package org.foo.domain;

public class BaseEntity {
  private int id;

  public int getId() {
    return id;
  }
}

package org.foo.data;

public class BaseEntity extends org.foo.domain.BaseEntity { // Noncompliant
  private String recordData;

  public String getRecordData() {
    return recordData;
  }
}

Example 3:​

Positive​

This positive example demonstrates a class uniquely named, avoiding conflicts with the superclass.

package org.foo.domain;

public class BaseEntity {
  private int id;

  public int getId() {
    return id;
  }
}

package org.foo.data;

import org.foo.domain.BaseEntity;

public class EntityRecord extends BaseEntity { // Compliant
  private String recordData;

  public String getRecordData() {
    return recordData;
  }
}