Why is this an issue?
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 rule admits 3 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;
}
The unused field in this class will not be reported by the rule as it is annotated.
public class MyClass {
@SomeAnnotation
private int unused;
}
- Fields from classes with native methods
The unused field in this class will not be reported by the rule as it might be used by native code.
public class MyClass {
private int unused = 42;
private native static void doSomethingNative();
}
