interview test

[Campbell Ritchie]

I am going to make things really difficult and assert that writing "ConceptA" in the toString method is a bug.
I challenge you to explain why I made that assertion.

I am also going to be awkward about names:
The naming of the classes Concept, Concept1, ConceptA, etc., is at best confusing and at worst a hazardous bug. I also think the names of the packages are misleading.

[sujesh Katri]

I used my own naming convention..i have corrected the errors in the code which was sent by the interviewer.
a)original code which was sent by interviewer:

com/result/exam/a/Concept.java
package com.result.exam.a;

public abstract class Concept
{
  private String id;

  protected Concept( String anId )
  {
    if ( anId == null ) 
    {
      throw new NullPointerException( "id must not be null" );
    }

    id = anId;
  }

  public String getId()
  {
    return id;
  }

  public void setId( final String id )
  {
    id = id;
  }

  public boolean equals( Object other )
  {
    return other != null && other.getClass().equals( getClass() ) && id.equals( ( (Concept) other ).id );
  }

  public String toString()
  {
    return "Concept(" + id + ")";
  }
}
com/result/exam/a/ConceptA.java
package com.result.exam.a;

public class ConceptA extends Concept
{
  private final Concept parent;

  public ConceptA( String anId, Concept aParent )
  {
    super( anId );

    parent = aParent;
  }

  public Concept getParent()
  {
    return parent;
  }

  public String toString()
  {
    return "ConceptA{" + getId() + ", parent=" + parent + '}';
  }
}
com/result/exam/a/ConceptB.java
package com.result.exam.a;

import java.util.Set;
import java.util.HashSet;
import java.util.Iterator;

public class ConceptB extends ConceptA
{
  private final Set children;

  public ConceptB( final String anId, final Concept aParent )
  {
    super( anId, aParent );

    children = new HashSet();
  }

  public int getCount()
  {
    return children.size();
  }

  public void addChild( Concept aChild )
  {
    children.add( aChild );
  }

  public void removeChild( Concept aChild )
  {
    children.remove( aChild );
  }

  public Iterator getChildren()
  {
    return children.iterator();
  }

  public int getFamilySize()
  {
    int count = children.size();

    for ( Iterator iter = getChildren(); iter.hasNext(); )
    {
      count += ( (ConceptB) iter.next() ).getFamilySize();
    }

    return count;
  }

  public int getAncestorCount()
  {
    int count = 0;
    Concept ancestor = getParent();

    while ( ancestor != null )
    {
      count++;
      if ( ancestor instanceof ConceptA )
      {
        ancestor = ( (ConceptA) ancestor ).getParent();
      }
      else
      {
        ancestor = null;
      }
    }

    return count;
  }

  public String toString()
  {
    return "ConceptB{" + getId() + ", parent=" + getParent() + ", children=" + children.size() + "}";
  }
}
com/result/exam/a/ConceptC.java
package com.result.exam.a;

public class ConceptC extends ConceptA
{
  private static int nextSerialNo = 0;

  public static int getNextSerialNo()
  {
    return nextSerialNo++;
  }

  private final int serialNo;

  public ConceptC( String anId )
  {
    super( anId, null );

    serialNo = getNextSerialNo();
  }

  public int getSerialNo()
  {
    return serialNo;
  }

  public String toString()
  {
    return "ConceptC(" + getId() + ", " + serialNo + ")";
  }
}

b)the code i have corrected is as below

package com.result.exam.a;

public abstract class Concept
{
  private String id;

  protected Concept( String anId )
  {
    if ( anId == null ) 
    {
      throw new NullPointerException( "id must not be null" );
    }

    id = anId;
  }

  public String getId()
  {
    return id;
  }

  public void setId( final String id )
  {
    this.id = id;
      if(this.id==null)
      {
          throw new NullPointerException("id must not be null");
      }
  
  }

  public boolean equals( Object other )
  {
    return other != null && other.getClass().equals( getClass() ) && id.equals( ( (Concept) other ).id );
  }

  public String toString()
  {
    return "Concept(" + id + ")";
  }
}

com/result/exam/a/ConceptA.java
package com.result.exam.a;

public class ConceptA extends Concept
{
  private final Concept parent;

  public ConceptA( String anId, Concept aParent )
  {
    super( anId );

    parent = aParent;
  }

  public Concept getParent()
  {
    return parent;
  }

  public String toString()
  {
    return "ConceptA{" + getId() + ", parent=" + parent + '}';
  }
}
com/result/exam/a/ConceptB.java
package com.result.exam.a;

import java.util.Set;
import java.util.HashSet;
import java.util.Iterator;

public class ConceptB extends ConceptA
{
  private final Set children;

  public ConceptB( String anId,Concept aParent )
  {
    super( anId, aParent );

    children = new HashSet();
  }

  public int getCount()
  {
    return children.size();
  }

  public void addChild( Concept aChild )
  {
    children.add( aChild );
  }

  public void removeChild( Concept aChild )
  {
    children.remove( aChild );
  }

  public Iterator getChildren()
  {
    return children.iterator();
  }

  public int getFamilySize()
  {
    int count = children.size();

    for ( Iterator iter = getChildren(); iter.hasNext(); )
    {
      count += ( (ConceptB) iter.next() ).getFamilySize();
    }

    return count;
  }

  public int getAncestorCount()
  {
    int count = 0;
    Concept ancestor = getParent();

    while ( ancestor != null )
    {
      count++;
      if ( ancestor instanceof ConceptA )
      {
        ancestor = ( (ConceptA) ancestor ).getParent();
      }
      else
      {
        ancestor = null;
      }
    }

    return count;
  }

  public String toString()
  {
    return "ConceptB{" + getId() + ", parent=" + getParent() + ", children=" + children.size() + "}";
  }
}
com/result/exam/a/ConceptC.java

public class ConceptC extends ConceptA
{
  private static int nextSerialNo = 0;

  public static int getNextSerialNo()
  {
    return nextSerialNo;
  }

  private final int serialNo;

  public ConceptC( String anId )
  {
    super( anId, null );

    serialNo = getNextSerialNo();
  }

  public int getSerialNo()
  {
    return serialNo;
  }

  public String toString()
  {
    return "ConceptC(" + getId() + ", " + serialNo + ")";
  }
 

can you please have a look at code (b) above and let me know if the code is correct?

[Campbell Ritchie]

sujesh Katri wrote:I used my own naming convention . . .

Very bad idea. An employer will expect you to use their code conventions. Using your own naming conventions means you will write code which other programmers cannot understand.

As Joanne has explained several times lines 24-27 are incorrect.
You should consider the use of getClass() in the equals method. Even I am coming to the belief that it is implicitly incorrect.
As I have already said, the use of those String literals in the toString method is (in my opinon) poor style.
Using a raw type in lines 76/82 is incorrect.
Returning an Iterator is dangerous.
Why are you counting supertypes? That sounds like something from non‑object‑oriented programming. You should have got them to explain that before you went anywhere near your method. And I can think of a better way to run that loop.
The nest serial number method does not return the next serial number.

[sujesh Katri]

In my system only i used my own naming convention...code (b) was the answer code which i sent to the interviewer...i used their given names while sending the answer.

[Campbell Ritchie]

And what about the other points?