Array Operations

This example is a good start to have a basic discussion on data structures and algorithm design.  Understanding array operations and its limitations must be established first in order to understand other concepts in data structures.

public class ArrayOperations{

private static final int SIZE=10,ROW=2,COLUMN=3;
private static String array1[][]={{"00 ","01 ","02 "},{"10 ","11 ","12 "}};
private static String array2[]=new String[SIZE];
private static int next=0;

public static void main(String[] args){
    //fill();
    //insert("First");
    //insert("Second");
    //insert("Third");
    //delete("Student10");
    //System.out.println(fetch("Student3"));
    //update('d',"Student3");
    majorOrder('c');
    majorOrder('r');
    System.out.println();
}

private static void fill(){
    for(int i=0;i<SIZE;i++){
        array2[i]=new String("Student"+(i+1));
        next++;
    }
}

private static void delete(String key){   //slow O(n) due to sequential search
   if(next!=0){
    int i=0;
    while(array2[i].equals(key)){
        i++;
    }
   
    for(int j=i;j<next-1;j++){
        array2[j]=array2[j+1];
    }
    next--;
    array2[next]=null; 
   }
}

private static void majorOrder(char order){       //slow O(n^2) due to sequential search
    int total=0;
    if(order=='c'){
        for(int i=0;i<ROW;i++){
            for(int j=0;j<COLUMN;j++){
               total++;
               if(array1[i][j].equals("02 ")) 
                    System.out.println("It took "+total+" operations to find it");
            }
        }
    }
    else if(order=='r'){
        for(int j=0;j<COLUMN;j++){
            for(int i=0;i<ROW;i++){
               total++;
               if(array1[i][j].equals("02 ")) 
                    System.out.println("It took "+total+" operations to find it");
            }
        }
    }
    else
        System.out.println("Wrong major order type, only \'r\' or \'c\' are allowed");
}

private static void insert(String str){
    array2[next++]=new String(str);
}

private static String fetch(String key){  //slow O(n) due to sequential search
    int i=0;
    while(!array2[i].equals(key)){
        i++;
    }
    return new String(array2[i]); //return deepcopy object
}

private static void update(char oper, String str){
    if(oper=='i'){
        insert(str);
    }
    else if(oper=='d'){
        delete(str);
    }
    else
        System.out.println("Wrong operation was specified, use \'i\' or \'d\' for insert or delete operation");
}
}

Java LinkedList

There is two different ways to get the elements of a LinkedList.  Use the ListIterator method if you just need to process the elements in a sequential order.  If you need to address a specific element, it is much better to address the specific element in the list instead of getting an element and testing its field to see if you have reached the proper item.  Performance wise it will be O(n) vs. O(1) and we all know that O(1) would be a much more desirable performance goal. 

import java.util.LinkedList;

import java.util.ListIterator;

public class DebugLinkedListIterator {

public static void main(String[] args) {

        LinkedList<String> linkedList = new LinkedList<String>();

        linkedList.add("First");

        linkedList.add("Second");

        linkedList.add("Third");

        linkedList.add("Fourth");

        System.out.println("ListIterator Way: ");

        ListIterator<String> listIterator = linkedList.listIterator();

        while (listIterator.hasNext()) {

            System.out.println(listIterator.next());

        }

        System.out.println("Loop Way: ");

        for (int i = 0; i < linkedList.size(); i++) {

            System.out.println(linkedList.get(i));

        }

}

}
 

For someone dealing with concept for the first time, the best way to learn is to look at a single node in the debugger and trace the value changes.  This example should help with the process.

import java.util.LinkedList;
import java.util.ListIterator;

public class DebugLinkedListIterator {
public static void main(String[] args) {

        LinkedList<String> linkedList = new LinkedList<String>();
        linkedList.add("First");

        System.out.println("ListIterator Way: ");
        ListIterator<String> listIterator = linkedList.listIterator();
        System.out.println(listIterator.next());
        System.out.println(listIterator.previous());
        System.out.println(listIterator.next());
        System.out.println(listIterator.previous());
        System.out.println(listIterator.next());

        System.out.println("Loop Way: ");
        System.out.println(linkedList.get(0));
        System.out.println(linkedList.get(0));
        System.out.println(linkedList.get(0));
        System.out.println(linkedList.get(0));
}
}

 This screen shot is a direct copy of the running debugger, so you can see where the numbers came from in the image above.