Java – Checkstyle: How to Resolve “Hidden Field” Error

checkstyleeclipsejava

I am getting this checkstyle error:

'serverURL' hides a field

in this

 private static void setServerURL(final String serverURL) {
    Utility.serverURL = serverURL;
 }

What could be the reason, and how to resolve it?

Best Answer

There is already a variable defined serverURL which is available to this method (additional to the formal parameter you are accepting). This is called "shadowing".

I think most Java programmers turn this check off, because it's not really that confusing.

For example, this would trigger the error:

public class Foo {
  private int bar = 0;

  public void someMethod(int bar) {
    // There are two bars!  All references in this method will use the parameter bar,
    // unless they are explicitly prefixed with 'this'.
    this.bar = bar;
  }
}

Related Solutions

Java – How to call one constructor from another in Java

Yes, it is possible:

public class Foo {
    private int x;

    public Foo() {
        this(1);
    }

    public Foo(int x) {
        this.x = x;
    }
}

To chain to a particular superclass constructor instead of one in the same class, use super instead of this. Note that you can only chain to one constructor, and it has to be the first statement in your constructor body.

See also this related question, which is about C# but where the same principles apply.

Java – a serialVersionUID and why should I use it

The docs for java.io.Serializable are probably about as good an explanation as you'll get:

The serialization runtime associates with each serializable class a version number, called a 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. If the receiver has loaded a class for the object that has a different serialVersionUID than that of the corresponding sender's class, then deserialization will result in an InvalidClassException. A serializable class can declare its own serialVersionUID explicitly by declaring a field named serialVersionUID that must be static, final, and of type long:

ANY-ACCESS-MODIFIER static final long serialVersionUID = 42L;

If a serializable class does not explicitly declare a serialVersionUID, then the serialization runtime will calculate a default serialVersionUID value for that class based on various aspects of the class, as described in the Java(TM) Object Serialization Specification. However, it is strongly recommended that all serializable classes explicitly declare serialVersionUID values, since the default serialVersionUID computation is highly sensitive to class details that may vary depending on compiler implementations, and can thus result in unexpected InvalidClassExceptions during deserialization. Therefore, to guarantee a consistent serialVersionUID value across different java compiler implementations, a serializable class must declare an explicit serialVersionUID value. It is also strongly advised that explicit serialVersionUID declarations use the private modifier where possible, since such declarations apply only to the immediately declaring class — serialVersionUID fields are not useful as inherited members.

Best Answer

Related Solutions

Java – How to call one constructor from another in Java

Java – a serialVersionUID and why should I use it

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