When there is no explicit constructor...

Main.java

public static void main() {
  // Java provides a "default" no-argument constructor for us.
  MyCoolShit coolShit = new MyCoolShit();
  // But, NEVER rely on it!

  System.out.println("Bool: " + coolShit.aBool);
  System.out.println("Int: " + coolShit.anInt);
  System.out.println("Double: " + coolShit.aDouble);
  System.out.println("Char: " + coolShit.aChar);
  System.out.println("String: " + coolShit.aString);
  System.out.println("Rectangle: " + coolShit.aRectangle);

  // This, however, will throw an exception:
  MyLessCoolShit otherShit = new MyLessCoolShit();
  // because once we have defined any constructor, the JVM no
  // longer provides the "default" one.
}

MyCoolShit.java

public class MyCoolShit {
   public bool aBool;
   public int anInt;
   public double aDouble;
   public char aChar;
   public String aString;
   public Rectangle aRectangle;
   // Note: Our class has no explicit constructor.
}

MyLessCoolShit.java

public class MyLessCoolShit extends MyCoolShit {

  public MyLessCoolShit(String str) {
    super();
    this.aString = str;
  }

}