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johnchaser

Posts: 21

Posted: Sun, 27th Nov 2005 13:50 Post subject: Need a little hep with my java coding!	Quick Quote Quote

All right I'm supposed to make a class called Stock and have an arry the size of 100. I also need to create constructors accessors and mutators. Well I've already done this part. Now the problem is I have implement Add, Search, Delete and Update functions. Here's my partial code: Link

sabalasa

Posts: 369
Location: EST

Posted: Thu, 1st Dec 2005 12:59 Post subject:

right.

Checked your code and here are my 2 cents.

First of all make you array dynamic. Instead of having an rigid array which size is immutable use a Collection...like a Set, List or Vector. These babys have dynamic size meaning that you can add and remove elements on the fly. With arrays when adding an element you have to first make a new array with the size of the old array + 1 and copy all elements from your old array to the new one and then add the new element. The same goes for deleting an element - make a new array with the size of the old array - 1 and copy the elments from the old array.

An example

Code:

import java.util.Vector;

class Element {
private String name;

public Element(String name) {
this.name=name;
}
public void setName (String name) {
this.name=name;
}

public String getName () {
return name;
}
}

class Main {
public static void main (String[] args) {
Vector v = new Vector();
for (int i = 0; i<100; i++) {
v.add(new Element("Foo"))
}
.
.
.
}
}

Removing is as easy as this

Code:

v.removeElementAt(i);

where i is the index of the element.

Updating goes like this

Code:

Element e = (Element) v.elementAt(i);
e.setName("bar");

Inserting an element

Quote:

Element e = new Element("Baz");
v.insertElementAt(i, e);

And if you still want an array representation of your collection

Quote:

Element[] arr = (Element[]) v.toArray(new Element[v.size()]);

BTW: the code tag is buggy Razz

Had to use quote tags after using code tag for 3 times Very Happy

rgds
Sabalasa

johnchaser

Posts: 21

Posted: Thu, 1st Dec 2005 16:16 Post subject:	Quick Quote Quote

Thanks Saba, however, I'm prefer to use array and if you don't mind can you please show it with array instead? Thank you.

sabalasa

Posts: 369
Location: EST

Posted: Fri, 2nd Dec 2005 18:40 Post subject:

Ok. you want it the hard way, don't you Very Happy

I've written an example app which does exactly the same things you need.
Here is the code for the array element:

Code:

public class Element {
private String name;

public Element(String name) {
   this.name=name;
}
public void setName (String name) {
   this.name=name;
}
public String getName () {
   return name;
}
/**
* This method is invoked by JRE when there
* is a need for a String representation of
* the object (System.out.println() for example).
* You can specify here which parameters represent your object.
* The only parameter here is name.
*
* @see java.lang.Object#toString()
*/
public String toString() {
   return name;
}
}

and the main app

Code:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
/** Initialize the array with 10 spaces (change it for your needs) */
private static Element[] elements = new Element[10];

/** reusable method for showing the menu (I added 2 options - Show and Quit) **/
private static void showMenu() {
   System.out.println("PLEASE MAKE YOUR SELECTION(A, S, D, H or Q):" );
   System.out.println("\n[A]dd new Record");
   System.out.println("[S]earch Record");
   System.out.println("[D]elete Record");
   System.out.println("[U]pdate Record");
   System.out.println("S[H]ow Records");
   System.out.println("[Q]uit");
   System.out.print("\n\nEnter Selection: ");
}

/** executes the program **/
private static void execute() {
   try {
      boolean breakOut = false;
      InputStreamReader reader = new InputStreamReader(System.in);
      BufferedReader input = new BufferedReader(reader);
      while (!breakOut) { //loop until breakOut is true then exit
         showMenu(); // after each loop we need to show the menu again
         String inp = (input.readLine()).toUpperCase();
         if (inp.equals("")) {
            continue; //if the user entered an empty string then keep on asking
         }
         System.out.println("\nYou selected: " + inp);
         switch(inp.charAt(0)) { //determine what the user has entered
            case 'A': addRecord(); break;
            case 'S': searchRecord(); break;
            case 'D': deleteRecord(); break;
            case 'U': updateRecord(); break;
            case 'H': showRecords(); break;
            case 'Q': breakOut = true; //raise the breakOut flag
            default: continue; //in all other cases continue to loop
         }
      }
   } catch (IOException e) { // if some input/output exception occured
      e.printStackTrace(); //print it out and exit
   }
}
/** adds a record **/
private static void addRecord () throws IOException {
   String name = getUserInput ("Enter the name for the new element: ");
   Element[] newArray = new Element[elements.length + 1]; //initialize a new array (old array length + 1)
   for (int i = 0; i < elements.length; i++) { //add all elements from the old array
      newArray[i] = elements[i];
   }
   newArray[newArray.length-1] = new Element(name); //add the new element to the end of the array
                                       //array indexes start from 0 and end with length - 1
                                       //fe. Arr[10] indexes are [0..9] not [1..10].
   elements = newArray; //assign new array
}

/** searches for a record **/
private static void searchRecord () throws IOException {
   String name = getUserInput ("Enter the name of the element: ");
   for (int i = 0; i < elements.length; i++) {
      if (elements[i].getName().equals(name)) { //if the element has the same name as entered..
         System.out.println(elements[i] + " is at position " + (i+1)); //print it out (i starts from 0 therefore + 1)
         return; //and exit the method
      }
   }
   System.out.println("Could not find an element with the name " + name); //tough shit :P
}
/** deletes a record **/
private static void deleteRecord () throws IOException {
   int idx;
   while (true) { //ask for the index
      idx = validateInput(getUserInput("Enter the index of the element: "));
      if (idx > 0)
         break;
   }
   Element[] newArray = new Element [elements.length - 1]; //create a new array (old size - 1)
   int newIdx = 0; //initialize an index for the new array.
               //Note that this one will not be increased when we hit the element with the index the user entered
   for (int i = 0; i < elements.length; i++) { //copy all other elements
      if (i != idx - 1) { //if its not the index the user entered.
                     //array indexes start with 0 and therefore we need to substract 1 from the number the user entered.
         newArray[newIdx] = elements[i]; //just copy the element
         newIdx++; //and increase the new index
      }
   }
   elements = newArray; //assign new array
}
/** updates a record **/
private static void updateRecord () throws IOException {
   int idx;
   String newName;
   while (true) { // get the index
      idx = validateInput(getUserInput("Enter the index of the element you want to update: "));
      if (idx > 0) { //and the name
         newName = getUserInput("Enter new name for the element: ");
         break;
      }
   }
   Element e = elements[idx-1]; //get the element from the array (-1 again from the user input)
   e.setName(newName); // update the name
}
/** prints out the records **/
private static void showRecords() {
   for (int i = 0; i < elements.length; i++) {
      System.out.println((i+1) + "-" + elements[i]); //i+1 because i starts from 0. Uses the toString method from the Element class
   }
}
/** reusable method for validating user input and convert it to int**/
private static int validateInput(String input) {
   int ret = -1; // -1 represents invalid input
   if (!input.equals("")) {
      try {
         ret = Integer.parseInt(input); //try to parse the input into int
         if ((ret - 1) < 0 || (ret - 1) >= elements.length) { //check if the number is between the array capacity
            System.out.println ("Index must be between 1 and " + elements.length + "!");
            ret = -1;
         }
      } catch (NumberFormatException nfe) { //if parsing failed
         System.out.println ("Not an integer: " + input);
      }
   }
   return ret;
}

/** reusable method for getting user input **/
private static String getUserInput(String displayString) throws IOException {
   String ret = null;
   InputStreamReader reader = new InputStreamReader(System.in);
   BufferedReader input = new BufferedReader(reader);
   while (true) { //infinite loop
      System.out.print (displayString);
      ret = input.readLine();
      if (!ret.equals("")) //if the user enters an empty string then ask again
         break; //break out the infinite loop
   }
   return ret;
}

public static void main(String args[]) {
   for (int i = 0; i < elements.length; i++)
      elements[i] = new Element("Foo" +( i + 1));
   execute();
}
}

It took me about half an hour and I also included comments because I do not know your current skill with Java.

have fun, and copy/paste this code and you should be just fine Very Happy

rgds
Sabalasa

[sYn]
[Moderator] Elitist

Posts: 8374

Posted: Fri, 2nd Dec 2005 20:26 Post subject:	Quick Quote Quote

Good man for helping !

sabalasa

Posts: 369
Location: EST

Posted: Fri, 2nd Dec 2005 21:06 Post subject:	Quick Quote Quote

NP! I'm a Java senior programmer and a mentor for beginners anyway rgds Sabalasa

sabalasa

Posts: 369
Location: EST

Posted: Fri, 2nd Dec 2005 21:11 Post subject:	Quick Quote Quote

Oh, by the way johnchaser... Just analyse the code, try to decompose it and try understand what some piece of code does and then...if you really want to be a Java guru ... expand this logic. For example create methods for sorting the array and for swapping element positions etc. Then you're ready to go for harder problems rgds Sabalasa

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