# V6090. Field 'A' is being used before it was initialized.

The analyzer has detected an access inside a class constructor to a field that has not been initialized yet.

In Java, all fields are implicitly initialized with default values of appropriate types. For reference types, this default value is 'null'.

Consider the following example:

    public class Test
    {
      private Object data;
      private DataProvider dataProvider;

      public Test(DataProvider provider)
      {
        this.data = dataProvider.get();
        this.dataProvider = dataProvider;
      }
    }

What is being accessed here is not a constructor parameter but a class field, which results in throwing a 'NullPointerException' every time this constructor is called. Fixed code:

    public class Test
    {
      private Object data;
      private DataProvider dataProvider;

      public Test(DataProvider provider)
      {
        this.data = provider.get();
        this.dataProvider = provider;
      }
    }

Another error related to the use of uninitialized reference fields is to compare them with 'null'. The conditions involved are either always true or always false, which signals an error in the program's logic.

    public class Test
    {
      private DataProvider dataProvider;

      public Test()
      {
        if (dataProvider != null)
        {
          dataProvider = new DataProvider();
        }
      }
    }

The analyzer will not issue this warning if the field is initialized explicitly – even if with the 'null' value.

This diagnostic is classified as:

CWE-665

You can look at examples of errors detected by the V6090 diagnostic.