What is dependency injection?

public SomeClass() {
    myObject = Factory.getObject();
}

public SomeClass (MyClass myObject) {
    this.myObject = myObject;
}

public class PersonService {
  public void addManager( Person employee, Person newManager ) { ... }
  public void removeManager( Person employee, Person oldManager ) { ... }
  public Group getGroupByManager( Person manager ) { ... }
}

public class GroupMembershipService() {
  public void addPersonToGroup( Person person, Group group ) { ... }
  public void removePersonFromGroup( Person person, Group group ) { ... }
}

class Car{
 private Wheel wh= new NepaliRubberWheel();
 private Battery bt= new ExcideBattery();
 //rest
}