Question

package abc;  class DependencyDataCollection {     private int sNo;     private String sessionID;     private int noOfDependency;     private int noOfRejection;     private int totalValue;      /** Creates a new instance of DependencyDataCollection */     public DependencyDataCollection(int sNo, String sessionID, int noOfDependency, int noOfRejection, int totalValue)     {         this.sNo = sNo;         this.sessionID = sessionID;         this.noOfDependency = noOfDependency;         this.noOfRejection = noOfRejection;         this.totalValue = totalValue;     }      public int getSNo()     {         return sNo;     }      public String getSessionID()     {         return sessionID;     }      public int getNoOfDependency()     {         return noOfDependency;     }      public int getNoOfRejection()     {         return noOfRejection;     }      public int getTotalValue()     {         return totalValue;     } }  public class DependencyStack {      LinkedList lList;      /** Creates a new instance of DependencyStack */     public DependencyStack()     {         lList = new LinkedList();     }      public void add(int sNo, String sessionID, int noOfDependency, int noOfRejection, int totalValue)     {         lList.add(new DependencyDataCollection(sNo,sessionID,noOfDependency,noOfRejection,totalValue));     }      public int size()     {         return lList.size();     }      public void show()     {         for(int i=0;i<lList.size();i++)         {             DependencyDataCollection ddc = (DependencyDataCollection)lList.get(i);             System.out.println(ddc.getSNo()+'   '+ddc.getSessionID()+'   '+ddc.getNoOfDependency()+'     '+ddc.getNoOfRejection()+'      '+ddc.getTotalValue());         }     }      public int returnIndexOfSession(String sessionID)     {         DependencyDataCollection ddc = null;         for(int i=0;i<lList.size();i++)         {             ddc = (DependencyDataCollection)lList.get(i);             if(ddc.getSessionID().equals(sessionID))                 break;         }         return ddc.getSNo();     }      public static void main(String args[])     {         DependencyStack ds = new DependencyStack();         ds.add(1,'a',0,0,0);         ds.add(2,'b',0,0,0);         ds.show();          //System.out.println(ds.returnIndexOfSession('a'));  //        DependencyDataCollection ddc = new DependencyDataCollection(1,'a',0,0,0); //        System.out.println(ds.indexOf(ddc));     } } 

This is a simple Linked List program in java which is using inbuilt linkedlist class from java.util package. The linked list is used to store different amount of data using DependencyDataCollection Class..

Now my question is

1) Please evaluate this program, and temme am i respecting all java concepts like private member access,which i have done, etc..

2) I am facing problem to find the indexOf a particular session.

For e.g. Node 1 contains 1,’a’,0,0,0……………Node 2 contains 2,’b’,0,0,0

Now i wanted to find the indexOf the node which is containing one of the data as ‘b’ or ‘a’. What could be the shortest inbuilt method which can do so, as i have made a function named ‘public int returnIndexOfSession(String sessionID)’ which makes use of for loop, i find this very time consuming.. Is there any other way out..

Please evaluate and guide as i am a newbie in java.

Answer 1

Here are the changes I would make, rationale is in the comments.

import java.io.OutputStream; import java.io.OutputStreamWriter; import java.io.PrintWriter; import java.io.Writer; import java.util.ArrayList; import java.util.List;   class DependencyDataCollection {     // makte them fnal, then you hava an immutible object and your code is much safer.     // in your case you had noset methods so it was safe, but always try to make things final.     private final int sNo;     private final String sessionID;     private final int noOfDependency;     private final int noOfRejection;     private final int totalValue;      public DependencyDataCollection(final int    sNo,                                      final String sessionID,                                      final int    noOfDependency,                                      final int    noOfRejection,                                      final int    totalValue)     {         this.sNo            = sNo;         this.sessionID      = sessionID;         this.noOfDependency = noOfDependency;         this.noOfRejection  = noOfRejection;         this.totalValue     = totalValue;     }      public int getSNo()     {         return sNo;     }      public String getSessionID()     {         return sessionID;     }      public int getNoOfDependency()     {         return noOfDependency;     }      public int getNoOfRejection()     {         return noOfRejection;     }      public int getTotalValue()     {         return totalValue;     } }  class DependencyStack {     // change the type to be as generic as poosible - List interface     // added generics so you get compile time safety and don't use casts later on     // renamed it to something meaningful     private final List<DependencyDataCollection> dependencies;      // use an ArrayList instead of a LinkedList, it'll be faster since you are not inserting/deleting     // into the middle of the list     {         dependencies = new ArrayList<DependencyDataCollection>();     }      // your Stack shouldn't know how to make the collections... (in my opinion)     public void add(final DependencyDataCollection ddc)     {         dependencies.add(ddc);     }      public int size()     {         return dependencies.size();     }      // the next 3 methods are just convenience since you don't know if someione     // will want to write to a file or a writer instead of a stream     public void show()     {         show(System.out);     }      public void show(final OutputStream out)     {         show(new OutputStreamWriter(out));     }      public void show(final Writer writer)     {         show(new PrintWriter(writer));     }      public void show(final PrintWriter writer)     {         // use the new for-each instead of the old style for loop         // this also uses an iterator which is faster than calling get         // (well on an ArrayList it probably is about the same, but a LinkedList it'll be faster)         for(final DependencyDataCollection ddc : dependencies)         {             writer.println(ddc.getSNo()            + '   ' +                            ddc.getSessionID()      + '   ' +                            ddc.getNoOfDependency() + '   ' +                            ddc.getNoOfRejection()  + '   ' +                            ddc.getTotalValue());         }     }      public int returnIndexOfSession(final String sessionID)     {         DependencyDataCollection foundDDC;         final int                retVal;          foundDDC = null;          for(final DependencyDataCollection ddc : dependencies)         {             if(ddc.getSessionID().equals(sessionID))             {                 foundDDC = ddc;                 break;             }         }          // deal with the fact that you might have not found the item and it would be null.         // this assumes -1 is an invalid session id         if(foundDDC == null)         {             retVal = -1;         }         else         {             retVal = foundDDC.getSNo();         }          return (retVal);     }      public static void main(final String[] args)     {         DependencyStack ds = new DependencyStack();         ds.add(new DependencyDataCollection(1,'a',0,0,0));         ds.add(new DependencyDataCollection(1,'a',0,0,0));         ds.show();          //System.out.println(ds.returnIndexOfSession('a'));  //        DependencyDataCollection ddc = new DependencyDataCollection(1,'a',0,0,0); //        System.out.println(ds.indexOf(ddc));     } } 

Edit:

This one will speed up the lookups (and deletes).

class DependencyStack {     // A Map provides quick lookup     private final Map<String, DependencyDataCollection> dependencies;      // a LinkedHashMap allows for quick lookup, but iterates in the order they were added... if that matters for show.     {         dependencies = new LinkedHashMap<String, DependencyDataCollection>();     }      // your Stack shouldn't know how to make the collections... (in my opinion)     public void add(final DependencyDataCollection ddc)     {         if(ddc == null)         {             throw new IllegalArgumentException('ddc cannot be null');         }          dependencies.put(ddc.getSessionID(), ddc);     }      public int size()     {         return dependencies.size();     }      // the next 3 methods are just convenience since you don't know if someione     // will want to write to a file or a writer instead of a stream     public void show()     {         show(System.out);     }      public void show(final OutputStream out)     {         show(new OutputStreamWriter(out));     }      public void show(final Writer writer)     {         show(new PrintWriter(writer));     }      public void show(final PrintWriter writer)     {         // use the new for-each instead of the old style for loop         // this also uses an iterator which is faster than calling get         // (well on an ArrayList it probably is about the same, but a LinkedList it'll be faster)         for(final DependencyDataCollection ddc : dependencies.values())         {             writer.println(ddc.getSNo()            + '   ' +                            ddc.getSessionID()      + '   ' +                            ddc.getNoOfDependency() + '   ' +                            ddc.getNoOfRejection()  + '   ' +                            ddc.getTotalValue());         }     }      public int returnIndexOfSession(final String sessionID)     {         final DependencyDataCollection ddc;         final int                      retVal;          if(sessionID == null)         {             throw new IllegalArgumentException('sessionID cannot be null');         }          // get it if it exists, this is much faster then looping through a list         ddc = dependencies.get(sessionID);          // deal with the fact that you might have not found the item and it would be null.         // this assumes -1 is an invalid session id         if(ddc == null)         {             retVal = -1;         }         else         {             retVal = ddc.getSNo();         }          return (retVal);     }      public static void main(final String[] args)     {         DependencyStack ds = new DependencyStack();         ds.add(new DependencyDataCollection(1,'a',0,0,0));         ds.add(new DependencyDataCollection(1,'a',0,0,0));         ds.show();          //System.out.println(ds.returnIndexOfSession('a'));  //        DependencyDataCollection ddc = new DependencyDataCollection(1,'a',0,0,0); //        System.out.println(ds.indexOf(ddc));     } }