Initials.java

import java.util.*;

public class Initials {

  private String foo = null;
  private int i = 0;
  private Map<String, Integer> map = null;

}

javap -c -classpath . Initials

Compiled from "Initials.java"
public class Initials {
  public Initials();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: aload_0
       5: aconst_null
       6: putfield      #2                  // Field foo:Ljava/lang/String;
       9: aload_0
      10: iconst_0
      11: putfield      #3                  // Field i:I
      14: aload_0
      15: aconst_null
      16: putfield      #4                  // Field map:Ljava/util/Map;
      19: return
}

javap -c -classpath . NotInitials

Compiled from "NotInitials.java"
public class NotInitials {
  public NotInitials();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return
}

NotInitials.java

import java.util.*;

public class NotInitials {
  private String foo;
  private int i;
  private Map<String, Integer> map;
}

Setting the fields to null (or their default) causes the fields to be initialized twice. This isn't the end of the world and is unlikely to break your application (and might even be optimized away when the app starts?) but, still.