prasadtalasila/BITS-Darshini

If a private field is declared but not used in the program, it can be considered dead code and should therefore be removed. This will improve maintainability because developers will not wonder what the variable is used for.

Note that this rule does not take reflection into account, which means that issues will be raised on private fields that are only accessed using the reflection API.

Noncompliant Code Example

public class MyClass {
  private int foo = 42;

  public int compute(int a) {
    return a * 42;
  }

}

Compliant Solution

public class MyClass {
  public int compute(int a) {
    return a * 42;
  }
}

Exceptions

The Java serialization runtime associates with each serializable class a version number, called serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization.

A serializable class can declare its own serialVersionUID explicitly by declaring a field named serialVersionUID that must be static, final, and of type long. By definition those serialVersionUID fields should not be reported by this rule:

public class MyClass implements java.io.Serializable {
  private static final long serialVersionUID = 42L;
}

Moreover, this rule doesn't raise any issue on annotated fields.

If a private field is declared but not used in the program, it can be considered dead code and should therefore be removed. This will improve maintainability because developers will not wonder what the variable is used for.

Note that this rule does not take reflection into account, which means that issues will be raised on private fields that are only accessed using the reflection API.

Noncompliant Code Example

public class MyClass {
  private int foo = 42;

  public int compute(int a) {
    return a * 42;
  }

}

Compliant Solution

public class MyClass {
  public int compute(int a) {
    return a * 42;
  }
}

Exceptions

The Java serialization runtime associates with each serializable class a version number, called serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization.

A serializable class can declare its own serialVersionUID explicitly by declaring a field named serialVersionUID that must be static, final, and of type long. By definition those serialVersionUID fields should not be reported by this rule:

public class MyClass implements java.io.Serializable {
  private static final long serialVersionUID = 42L;
}

Moreover, this rule doesn't raise any issue on annotated fields.

Duplicated string literals make the process of refactoring error-prone, since you must be sure to update all occurrences.

On the other hand, constants can be referenced from many places, but only need to be updated in a single place.

Noncompliant Code Example

With the default threshold of 3:

public void run() {
  prepare("action1");                              // Noncompliant - "action1" is duplicated 3 times
  execute("action1");
  release("action1");
}

@SuppressWarning("all")                            // Compliant - annotations are excluded
private void method1() { /* ... */ }
@SuppressWarning("all")
private void method2() { /* ... */ }

public String method3(String a) {
  System.out.println("'" + a + "'");               // Compliant - literal "'" has less than 5 characters and is excluded
  return "";                                       // Compliant - literal "" has less than 5 characters and is excluded
}

Compliant Solution

private static final String ACTION_1 = "action1";  // Compliant

public void run() {
  prepare(ACTION_1);                               // Compliant
  execute(ACTION_1);
  release(ACTION_1);
}

Exceptions

To prevent generating some false-positives, literals having less than 5 characters are excluded.

If a private field is declared but not used in the program, it can be considered dead code and should therefore be removed. This will improve maintainability because developers will not wonder what the variable is used for.

Note that this rule does not take reflection into account, which means that issues will be raised on private fields that are only accessed using the reflection API.

Noncompliant Code Example

public class MyClass {
  private int foo = 42;

  public int compute(int a) {
    return a * 42;
  }

}

Compliant Solution

public class MyClass {
  public int compute(int a) {
    return a * 42;
  }
}

Exceptions

The Java serialization runtime associates with each serializable class a version number, called serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization.

A serializable class can declare its own serialVersionUID explicitly by declaring a field named serialVersionUID that must be static, final, and of type long. By definition those serialVersionUID fields should not be reported by this rule:

public class MyClass implements java.io.Serializable {
  private static final long serialVersionUID = 42L;
}

Moreover, this rule doesn't raise any issue on annotated fields.

Overriding or shadowing a variable declared in an outer scope can strongly impact the readability, and therefore the maintainability, of a piece of code. Further, it could lead maintainers to introduce bugs because they think they're using one variable but are really using another.

Noncompliant Code Example

class Foo {
  public int myField;

  public void doSomething() {
    int myField = 0;
    ...
  }
}

See

• CERT, DCL01-C. - Do not reuse variable names in subscopes
• CERT, DCL51-J. - Do not shadow or obscure identifiers in subscopes

If a private field is declared but not used in the program, it can be considered dead code and should therefore be removed. This will improve maintainability because developers will not wonder what the variable is used for.

Note that this rule does not take reflection into account, which means that issues will be raised on private fields that are only accessed using the reflection API.

Noncompliant Code Example

public class MyClass {
  private int foo = 42;

  public int compute(int a) {
    return a * 42;
  }

}

Compliant Solution

public class MyClass {
  public int compute(int a) {
    return a * 42;
  }
}

Exceptions

The Java serialization runtime associates with each serializable class a version number, called serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization.

A serializable class can declare its own serialVersionUID explicitly by declaring a field named serialVersionUID that must be static, final, and of type long. By definition those serialVersionUID fields should not be reported by this rule:

public class MyClass implements java.io.Serializable {
  private static final long serialVersionUID = 42L;
}

Moreover, this rule doesn't raise any issue on annotated fields.

If a private field is declared but not used in the program, it can be considered dead code and should therefore be removed. This will improve maintainability because developers will not wonder what the variable is used for.

Note that this rule does not take reflection into account, which means that issues will be raised on private fields that are only accessed using the reflection API.

Noncompliant Code Example

public class MyClass {
  private int foo = 42;

  public int compute(int a) {
    return a * 42;
  }

}

Compliant Solution

public class MyClass {
  public int compute(int a) {
    return a * 42;
  }
}

Exceptions

The Java serialization runtime associates with each serializable class a version number, called serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization.

A serializable class can declare its own serialVersionUID explicitly by declaring a field named serialVersionUID that must be static, final, and of type long. By definition those serialVersionUID fields should not be reported by this rule:

public class MyClass implements java.io.Serializable {
  private static final long serialVersionUID = 42L;
}

Moreover, this rule doesn't raise any issue on annotated fields.

If a private field is declared but not used in the program, it can be considered dead code and should therefore be removed. This will improve maintainability because developers will not wonder what the variable is used for.

Note that this rule does not take reflection into account, which means that issues will be raised on private fields that are only accessed using the reflection API.

Noncompliant Code Example

public class MyClass {
  private int foo = 42;

  public int compute(int a) {
    return a * 42;
  }

}

Compliant Solution

public class MyClass {
  public int compute(int a) {
    return a * 42;
  }
}

Exceptions

The Java serialization runtime associates with each serializable class a version number, called serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization.

A serializable class can declare its own serialVersionUID explicitly by declaring a field named serialVersionUID that must be static, final, and of type long. By definition those serialVersionUID fields should not be reported by this rule:

public class MyClass implements java.io.Serializable {
  private static final long serialVersionUID = 42L;
}

Moreover, this rule doesn't raise any issue on annotated fields.

If a private field is declared but not used in the program, it can be considered dead code and should therefore be removed. This will improve maintainability because developers will not wonder what the variable is used for.

Note that this rule does not take reflection into account, which means that issues will be raised on private fields that are only accessed using the reflection API.

Noncompliant Code Example

public class MyClass {
  private int foo = 42;

  public int compute(int a) {
    return a * 42;
  }

}

Compliant Solution

public class MyClass {
  public int compute(int a) {
    return a * 42;
  }
}

Exceptions

The Java serialization runtime associates with each serializable class a version number, called serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization.

A serializable class can declare its own serialVersionUID explicitly by declaring a field named serialVersionUID that must be static, final, and of type long. By definition those serialVersionUID fields should not be reported by this rule:

public class MyClass implements java.io.Serializable {
  private static final long serialVersionUID = 42L;
}

Moreover, this rule doesn't raise any issue on annotated fields.

If a private field is declared but not used in the program, it can be considered dead code and should therefore be removed. This will improve maintainability because developers will not wonder what the variable is used for.

Note that this rule does not take reflection into account, which means that issues will be raised on private fields that are only accessed using the reflection API.

Noncompliant Code Example

public class MyClass {
  private int foo = 42;

  public int compute(int a) {
    return a * 42;
  }

}

Compliant Solution

public class MyClass {
  public int compute(int a) {
    return a * 42;
  }
}

Exceptions

The Java serialization runtime associates with each serializable class a version number, called serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization.

A serializable class can declare its own serialVersionUID explicitly by declaring a field named serialVersionUID that must be static, final, and of type long. By definition those serialVersionUID fields should not be reported by this rule:

public class MyClass implements java.io.Serializable {
  private static final long serialVersionUID = 42L;
}

Moreover, this rule doesn't raise any issue on annotated fields.

Programmers should not comment out code as it bloats programs and reduces readability.

Unused code should be deleted and can be retrieved from source control history if required.

If a private field is declared but not used in the program, it can be considered dead code and should therefore be removed. This will improve maintainability because developers will not wonder what the variable is used for.

Note that this rule does not take reflection into account, which means that issues will be raised on private fields that are only accessed using the reflection API.

Noncompliant Code Example

public class MyClass {
  private int foo = 42;

  public int compute(int a) {
    return a * 42;
  }

}

Compliant Solution

public class MyClass {
  public int compute(int a) {
    return a * 42;
  }
}

Exceptions

The Java serialization runtime associates with each serializable class a version number, called serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization.

A serializable class can declare its own serialVersionUID explicitly by declaring a field named serialVersionUID that must be static, final, and of type long. By definition those serialVersionUID fields should not be reported by this rule:

public class MyClass implements java.io.Serializable {
  private static final long serialVersionUID = 42L;
}

Moreover, this rule doesn't raise any issue on annotated fields.

If a private field is declared but not used in the program, it can be considered dead code and should therefore be removed. This will improve maintainability because developers will not wonder what the variable is used for.

Note that this rule does not take reflection into account, which means that issues will be raised on private fields that are only accessed using the reflection API.

Noncompliant Code Example

public class MyClass {
  private int foo = 42;

  public int compute(int a) {
    return a * 42;
  }

}

Compliant Solution

public class MyClass {
  public int compute(int a) {
    return a * 42;
  }
}

Exceptions

The Java serialization runtime associates with each serializable class a version number, called serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization.

A serializable class can declare its own serialVersionUID explicitly by declaring a field named serialVersionUID that must be static, final, and of type long. By definition those serialVersionUID fields should not be reported by this rule:

public class MyClass implements java.io.Serializable {
  private static final long serialVersionUID = 42L;
}

Moreover, this rule doesn't raise any issue on annotated fields.

Programmers should not comment out code as it bloats programs and reduces readability.

Unused code should be deleted and can be retrieved from source control history if required.

Correctly updating a static field from a non-static method is tricky to get right and could easily lead to bugs if there are multiple class instances and/or multiple threads in play. Ideally, static fields are only updated from synchronized static methods.

This rule raises an issue each time a static field is updated from a non-static method.

Noncompliant Code Example

public class MyClass {

  private static int count = 0;

  public void doSomething() {
    //...
    count++;  // Noncompliant
  }
}

Utility classes, which are collections of static members, are not meant to be instantiated. Even abstract utility classes, which can be extended, should not have public constructors.

Java adds an implicit public constructor to every class which does not define at least one explicitly. Hence, at least one non-public constructor should be defined.

Noncompliant Code Example

class StringUtils { // Noncompliant

  public static String concatenate(String s1, String s2) {
    return s1 + s2;
  }

}

Compliant Solution

class StringUtils { // Compliant

  private StringUtils() {
    throw new IllegalStateException("Utility class");
  }

  public static String concatenate(String s1, String s2) {
    return s1 + s2;
  }

}

Exceptions

When class contains public static void main(String[] args) method it is not considered as utility class and will be ignored by this rule.

If a private field is declared but not used in the program, it can be considered dead code and should therefore be removed. This will improve maintainability because developers will not wonder what the variable is used for.

Note that this rule does not take reflection into account, which means that issues will be raised on private fields that are only accessed using the reflection API.

Noncompliant Code Example

public class MyClass {
  private int foo = 42;

  public int compute(int a) {
    return a * 42;
  }

}

Compliant Solution

public class MyClass {
  public int compute(int a) {
    return a * 42;
  }
}

Exceptions

The Java serialization runtime associates with each serializable class a version number, called serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization.

A serializable class can declare its own serialVersionUID explicitly by declaring a field named serialVersionUID that must be static, final, and of type long. By definition those serialVersionUID fields should not be reported by this rule:

public class MyClass implements java.io.Serializable {
  private static final long serialVersionUID = 42L;
}

Moreover, this rule doesn't raise any issue on annotated fields.

Utility classes, which are collections of static members, are not meant to be instantiated. Even abstract utility classes, which can be extended, should not have public constructors.

Java adds an implicit public constructor to every class which does not define at least one explicitly. Hence, at least one non-public constructor should be defined.

Noncompliant Code Example

class StringUtils { // Noncompliant

  public static String concatenate(String s1, String s2) {
    return s1 + s2;
  }

}

Compliant Solution

class StringUtils { // Compliant

  private StringUtils() {
    throw new IllegalStateException("Utility class");
  }

  public static String concatenate(String s1, String s2) {
    return s1 + s2;
  }

}

Exceptions

When class contains public static void main(String[] args) method it is not considered as utility class and will be ignored by this rule.

If a private field is declared but not used in the program, it can be considered dead code and should therefore be removed. This will improve maintainability because developers will not wonder what the variable is used for.

Note that this rule does not take reflection into account, which means that issues will be raised on private fields that are only accessed using the reflection API.

Noncompliant Code Example

public class MyClass {
  private int foo = 42;

  public int compute(int a) {
    return a * 42;
  }

}

Compliant Solution

public class MyClass {
  public int compute(int a) {
    return a * 42;
  }
}

Exceptions

The Java serialization runtime associates with each serializable class a version number, called serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization.

A serializable class can declare its own serialVersionUID explicitly by declaring a field named serialVersionUID that must be static, final, and of type long. By definition those serialVersionUID fields should not be reported by this rule:

public class MyClass implements java.io.Serializable {
  private static final long serialVersionUID = 42L;
}

Moreover, this rule doesn't raise any issue on annotated fields.

Programmers should not comment out code as it bloats programs and reduces readability.

Unused code should be deleted and can be retrieved from source control history if required.