freeacs/freeacs

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.

Even if it is technically possible, Restricted Identifiers should not be used as identifiers. This is only possible for compatibility reasons, using it in Java code is confusing and should be avoided.

Note that this applies to any version of Java, including the one where these identifiers are not yet restricted, to avoid future confusion.

This rule reports an issue when restricted identifiers:

• var
• yield
• record

are used as identifiers.

Noncompliant Code Example

var var = "var"; // Noncompliant: compiles but this code is confusing
var = "what is this?";

int yield(int i) { // Noncompliant
  return switch (i) {
    case 1: yield(0); // This is a yield from switch expression, not a recursive call.
    default: yield(i-1);
  };
}

String record = "record"; // Noncompliant

Compliant Solution

var myVariable = "var";

int minusOne(int i) {
  return switch (i) {
    case 1: yield(0);
    default: yield(i-1);
  };
}

String myRecord = "record";

See

• JLS16, 3.8: Identifiers

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.

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.

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.

Not all classes in the standard Java library were written to be thread-safe. Using them in a multi-threaded manner is highly likely to cause data problems or exceptions at runtime.

This rule raises an issue when an instance of Calendar, DateFormat, javax.xml.xpath.XPath, or javax.xml.validation.SchemaFactory is marked static.

Noncompliant Code Example

public class MyClass {
  private static SimpleDateFormat format = new SimpleDateFormat("HH-mm-ss");  // Noncompliant
  private static Calendar calendar = Calendar.getInstance();  // Noncompliant

Compliant Solution

public class MyClass {
  private SimpleDateFormat format = new SimpleDateFormat("HH-mm-ss");
  private Calendar calendar = Calendar.getInstance();

Cognitive Complexity is a measure of how hard the control flow of a method is to understand. Methods with high Cognitive Complexity will be difficult to maintain.

See

• Cognitive Complexity

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.

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.

Cognitive Complexity is a measure of how hard the control flow of a method is to understand. Methods with high Cognitive Complexity will be difficult to maintain.

See

• Cognitive Complexity

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.