Before you look at ArrayList Java code example, I would like to warn you that when you use ArrayList and other Java collections classes it is very easy to lose control over the size of used collection... This situation can lead to very random behaved Java performance problems. Your best helpers here are Java profilers and performance monitoring, reporting tools. For example, NetBeans Profiler for analysing Java applications, WebSphere Studio Profiling Tool.
NetBeans Profiler is a project to integrate the JFluid profiling technoglogy, which is being developed by Sun, into the NetBeans IDE. The JFluid technology addresses this issue by providing a mechanism in the JVM(tm), which allows the user to turn profiling on and off at any time, and, equally important, to profile just a small subset of the code, that they are currently interested in. The profiled subset of the code and the type of profiling (CPU, memory, etc.) can be changed at any moment at run time. This is achieved mainly through dynamic bytecode instrumentation. Features include low overhead profiling, attaching to running applications, CPU Performance profiling, memory profiling, memory leak debugging and task-based profiling.
The Heap Analysis Tool (HAT) helps to debug unnecessary object retention (sometimes called "memory leaks") by providing a convenient means to browse the object topology in a heap snapshot, which is generated by the Java VM. HAT reads a hprof file, then sets itself up as a web server--therefore allowing you to run queries against a heap dump contained within the hprof file.
HAT has now been included with Java SE. Starting with Java SE 6, HAT has been replaced with jhat, which is included with the standard Sun distribution. HAT is not being maintained in a stand-alone configuration. Source code for jhat is available with the current release of Java SE.
When you profile, you need the most powerful tool you can get. At the same time, you do not want to spend time learning how to use the tool. JProfiler is just that: simple and powerful at the same time. With JProfiler you can immediately observe profiling data as your application is running. CPU, memory and thread profiling views are updated live and can be inspected without the need to wait for the measurement to complete. Finding a memory leak can be impossible without the right tool. JProfiler's heap walker offers you an intuitive interface to solve both simple and complex memory problems.
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// -----------------------------------------------------------------------------
// ArrayListExample.java
// -----------------------------------------------------------------------------
/*
* =============================================================================
* Copyright (c) 1998-2005 Jeffrey M. Hunter. All rights reserved.
*
* All source code and material located at the Internet address of
* http://www.idevelopment.info is the copyright of Jeffrey M. Hunter, 2005 and
* is protected under copyright laws of the United States. This source code may
* not be hosted on any other site without my express, prior, written
* permission. Application to host any of the material elsewhere can be made by
* contacting me at jhunter@idevelopment.info.
*
* I have made every effort and taken great care in making sure that the source
* code and other content included on my web site is technically accurate, but I
* disclaim any and all responsibility for any loss, damage or destruction of
* data or any other property which may arise from relying on it. I will in no
* case be liable for any monetary damages arising from such loss, damage or
* destruction.
*
* As with any code, ensure to test this code in a development environment
* before attempting to run it in production.
* =============================================================================
*/
import java.util.List;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.ListIterator;
import java.util.Collections;
import java.util.Random;
/**
* -----------------------------------------------------------------------------
* The following class provides an example of storing and retrieving objects
* from an ArrayList.
*
* A List corresponds to an "ordered" group of elements where duplicates are
* allowed.
*
* An ArrayList is a good choice for simple sequences.
* It is an Array based implementation where elements of the List can be
* accessed directly through get() and set() methods.
*
* ArrayList's give great performance on get() and set() methods, but do not
* perform well on add() and remove() methods when compared to a LinkedList.
*
* @version 1.0
* @author Jeffrey M. Hunter (jhunter@idevelopment.info)
* @author http://www.idevelopment.info
* -----------------------------------------------------------------------------
*/
public class ArrayListExample {
/**
* Provides an example of how to work with the ArrayList container.
*/
public void doArrayListExample() {
final int MAX = 10;
int counter = 0;
System.out.println("+---------------------------------------------------------------------+");
System.out.println("| Create/Store objects in an ArrayList container. |");
System.out.println("+---------------------------------------------------------------------+");
System.out.println();
List listA = new ArrayList();
List listB = new ArrayList();
for (int i = 0; i < MAX; i++) {
System.out.println(" - Storing Integer(" + i + ")");
listA.add(new Integer(i));
}
System.out.println(" - Storing String(Alex)");
listA.add("Alex");
System.out.println(" - Storing String(Melody)");
listA.add("Melody");
System.out.println(" - Storing String(Jeff)");
listA.add("Jeff");
System.out.println(" - Storing String(Alex)");
listA.add("Alex");
System.out.println();
System.out.println("+---------------------------------------------------------------------+");
System.out.println("| Retrieve objects in an ArrayList container using an Iterator. |");
System.out.println("+---------------------------------------------------------------------+");
System.out.println();
Iterator i = listA.iterator();
while (i.hasNext()) {
System.out.println(i.next());
}
System.out.println();
System.out.println("+---------------------------------------------------------------------+");
System.out.println("| Retrieve objects in an ArrayList container using a ListIterator. |");
System.out.println("+---------------------------------------------------------------------+");
System.out.println();
counter = 0;
ListIterator li = listA.listIterator();
while (li.hasNext()) {
System.out.println("Element [" + counter + "] = " + li.next());
System.out.println(" - hasPrevious = " + li.hasPrevious());
System.out.println(" - hasNext = " + li.hasNext());
System.out.println(" - previousIndex = " + li.previousIndex());
System.out.println(" - nextIndex = " + li.nextIndex());
System.out.println();
counter++;
}
System.out.println();
System.out.println("+---------------------------------------------------------------------+");
System.out.println("| Retrieve objects in an ArrayList container using index. |");
System.out.println("+---------------------------------------------------------------------+");
System.out.println();
for (int j=0; j < listA.size(); j++) {
System.out.println("[" + j + "] - " + listA.get(j));
}
System.out.println();
System.out.println("+---------------------------------------------------------------------+");
System.out.println("| Search for a particular Object and return its index location. |");
System.out.println("+---------------------------------------------------------------------+");
System.out.println();
int locationIndex = listA.indexOf("Jeff");
System.out.println("Index location of the String \"Jeff\" is: " + locationIndex);
System.out.println();
System.out.println("+---------------------------------------------------------------------+");
System.out.println("| Search for an object and return the first and last (highest) index. |");
System.out.println("+---------------------------------------------------------------------+");
System.out.println();
System.out.println("First occurance search for String \"Alex\". Index = " + listA.indexOf("Alex"));
System.out.println("Last Index search for String \"Alex\". Index = " + listA.lastIndexOf("Alex"));
System.out.println();
System.out.println("+---------------------------------------------------------------------+");
System.out.println("| Extract a sublist from the main list, then print the new List. |");
System.out.println("+---------------------------------------------------------------------+");
System.out.println();
List listSub = listA.subList(10, listA.size());
System.out.println("New Sub-List from index 10 to " + listA.size() + ": " + listSub);
System.out.println();
System.out.println("+---------------------------------------------------------------------+");
System.out.println("| Sort the Sub-List created above. |");
System.out.println("+---------------------------------------------------------------------+");
System.out.println();
System.out.println("Original List : " + listSub);
Collections.sort(listSub);
System.out.println("New Sorted List : " + listSub);
System.out.println();
System.out.println();
System.out.println("+---------------------------------------------------------------------+");
System.out.println("| Reverse the Sub-List created above. |");
System.out.println("+---------------------------------------------------------------------+");
System.out.println();
System.out.println("Original List : " + listSub);
Collections.reverse(listSub);
System.out.println("New Reversed List : " + listSub);
System.out.println();
System.out.println();
System.out.println("+---------------------------------------------------------------------+");
System.out.println("| Check to see if the Lists are empty. |");
System.out.println("+---------------------------------------------------------------------+");
System.out.println();
System.out.println("Is List A empty? " + listA.isEmpty());
System.out.println("Is List B empty? " + listB.isEmpty());
System.out.println("Is Sub-List empty? " + listSub.isEmpty());
System.out.println();
System.out.println("+---------------------------------------------------------------------+");
System.out.println("| Clone the initial List. |");
System.out.println("| NOTE: The contents of the List are object references, so both |");
System.out.println("| of the List's contain the same exact object reference's. |");
System.out.println("+---------------------------------------------------------------------+");
System.out.println();
System.out.println("List A (before) : " + listA);
System.out.println("List B (before) : " + listB);
System.out.println("Sub-List (before) : " + listSub);
System.out.println();
System.out.println("Are List's A and B equal? " + listA.equals(listB));
System.out.println();
listB = new ArrayList(listA);
System.out.println("List A (after) : " + listA);
System.out.println("List B (after) : " + listB);
System.out.println("Sub-List (after) : " + listSub);
System.out.println();
System.out.println("Are List's A and B equal? " + listA.equals(listB));
System.out.println();
System.out.println("+---------------------------------------------------------------------+");
System.out.println("| Shuffle the elements around in some Random order for List A. |");
System.out.println("+---------------------------------------------------------------------+");
System.out.println();
System.out.println("List A (before) : " + listA);
System.out.println("List B (before) : " + listB);
System.out.println("Sub-List (before) : " + listSub);
System.out.println();
System.out.println("Are List's A and B equal? " + listA.equals(listB));
System.out.println();
Collections.shuffle(listA, new Random());
System.out.println("List A (after) : " + listA);
System.out.println("List B (after) : " + listB);
System.out.println("Sub-List (after) : " + listSub);
System.out.println();
System.out.println("Are List's A and B equal? " + listA.equals(listB));
System.out.println();
System.out.println("+---------------------------------------------------------------------+");
System.out.println("| Convert a List to an Array. |");
System.out.println("+---------------------------------------------------------------------+");
System.out.println();
Object[] objArray = listA.toArray();
for (int j=0; j < objArray.length; j++) {
System.out.println("Array Element [" + j + "] = " + objArray[j]);
}
System.out.println();
System.out.println("+---------------------------------------------------------------------+");
System.out.println("| Remove (clear) Elements from List A. |");
System.out.println("+---------------------------------------------------------------------+");
System.out.println();
System.out.println("List A (before) : " + listA);
System.out.println("List B (before) : " + listB);
System.out.println();
listA.clear();
System.out.println("List A (after) : " + listA);
System.out.println("List B (after) : " + listB);
System.out.println();
}
/**
* Sole entry point to the class and application.
* @param args Array of String arguments.
*/
public static void main(String[] args) {
ArrayListExample listExample = new ArrayListExample();
listExample.doArrayListExample();
}
}
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