ArrayList vs LinkedList
Can anyone explain with a real time example where these will be used , & whats the difference between them....
1 ) ArrayList (vs) LinkedList (vs) Collection
2 ) Abstract Class (vs) Interface
Some more to add to that .,
Abstract class vs Interfaces
Extending threads vs Implementing runnable interface
HashTable vs HashMap
Iterator vs Enumeration
string vs StringBuffer
Reflections vs Introspection
Array vs Vector
ArrayList vs LinkedList
Throw vs Throws
can anyone help me in this regard?Most or all of these should be addressed in one of the following or in a google search of the exact terms. Do some research on your own, and then come back with more specific questions. These forums are not a particularly effective substitute for attending class or reading a textbook.
Sun's basic Java tutorial
Sun's New To Java Center. Includes an overview of what Java is, instructions for setting up Java, an intro to programming (that includes links to the above tutorial or to parts of it), quizzes, a list of resources, and info on certification and courses.
http://javaalmanac.com. A couple dozen code examples that supplement The Java Developers Almanac.
jGuru. A general Java resource site. Includes FAQs, forums, courses, more.
JavaRanch. To quote the tagline on their homepage: "a friendly place for Java greenhorns." FAQs, forums (moderated, I believe), sample code, all kinds of goodies for newbies. From what I've heard, they live up to the "friendly" claim.
Bruce Eckel's Thinking in Java (Available online.)
Joshua Bloch's Effective Java
Bert Bates and Kathy Sierra's Head First Java.
Similar Messages
-
Which is better? ArrayList or LinkedList
Do you know which one is better between ArrayList and LinkdedList in terms of performance, speed and capacity?
Which one do you suggest to use ?
ThanksIt depends upon how the list is going to be used. ArrayLists and LinkedLists work differently -- you need to think about how they each store their data.
ArrayLists store their list items in, well, arrays. This makes them very fast at addressing those items by index #. So any implementation that needs a lot of random access to the list, such as sorting, is going to be relatively fast.
The downside of storing the list in an array presents itself when it comes time to add more items to the list. When it runs out of space in the array, it must create a new larger array and copy the items over to it. Also, if you need to insert or remove an item anywhere other than the end of the list, ArrayList must shift the subsequent items in the list by doing an array copy.
This can be a real drag if you're implementing a queue. This is where LinkedList shines. Each item in the list points to the next and previous ones in the list. Inserting, appending or removing list items involves a couple simple assignment statements. No reallocations or large memory copies are involved. Access is easy as long as it is sequential.
Random access in a linked list is problematic however. In order to get to the Nth item in the list, LinkedList must start with the first item in the list and step through the list N-1 times. An order of magnitude slower than using an ArrayList. -
Both of the advantages of ArrayList and LinkedList are needed.
Hi there,
I wonder how if I want performance on random access an ArrayList and also remove elements in any position of the List? As far as I know that a LinkedList is the best choice if I want to remove elements in any position of the List, but it's slow on traversing the List. Sometimes it's hard to choose between ArrayList and LinkedList, is there a way that I could have both advantages of ArrayList and LinkedList?
Any suggestion?
Thanks,
JaxI think you might be interested in the data structure
called a deque. It is built for fast insertions
at both ends and is usually implemented as a linked
list of arrays. The standard collections API does not
offer this data structure (I wish it did). So you have
to find a 3rd party implementation. Try searching
Google: http://www.google.com/search?q=java+deque
Thanks nasch and pervel for the information. What do you think if I do something like this?
List a = new ArrayList();
// perform some tasks that is fast with ArrayList
List b = new LinkedList(a);
// perform some tasks..
Although a new object is created, but that perform better than one ArrayList or one LinkedList solely. -
When to choose ArrayList and LinkedList ?
Please let me know which list type to use and when ? Pros Cons .. Advantages Disadvantages
ArrayList vs LinkedList ?Here is a good place to start [http://www.google.co.uk/search?q=arraylist+vs+linkedlist] 154,000 hits. I think most of the arguments are covered here. ;]
-
Design choice between ArrayList and LinkedList
Can someone clarify me which is better suited (efficient) for use?
It appears to me that both can be used very much interchangeably at least from functionality point of view. :(Using the following code (and I'm sure someone will come nitpicking about it) I get the (expected, at least by me from prior experience) result that iteration over a LinkedList is about twice as fast as iteration over an ArrayList, but lookup operations on an ArrayList are substantially faster:
package jtw.test;
import java.util.*;
public class SpeedTest {
public static void main(String... args) throws Exception {
List<Integer> linked = new LinkedList<Integer>();
List<Integer> arr = new ArrayList<Integer>();
for (int i = 0; i < 1e3; i++) {
linked.add(i);
arr.add(i);
long r = 0;
Date startLinked = new Date();
for (int i = 0; i < 1e3; i++) {
for (Integer q: linked) {
r += q;
Date stopLinked = new Date();
System.out.println("Total: " + r);
r = 0;
Date startArr = new Date();
for (int i = 0; i < 1e3; i++) {
for (Integer q: arr) {
r += q;
Date stopArr = new Date();
System.out.println("Total: " + r);
System.out.println("LinkedList iteration: " + startLinked + " to " + stopLinked + " took " + (stopLinked.getTime() - startLinked.getTime()));
System.out.println(" ArrayList iteration: " + startArr + " to " + stopArr + " took " + (stopArr.getTime() - startArr.getTime()));
r = 0;
startLinked = new Date();
for (int i = 0; i < 1e3; i++) {
for (int j = 999; j >= 0; j--) {
r += linked.get(j);
stopLinked = new Date();
System.out.println("Total: " + r);
r = 0;
startArr = new Date();
for (int i = 0; i < 1e3; i++) {
for (int j = 999; j >= 0; j--) {
r += arr.get(j);
stopArr = new Date();
System.out.println("Total: " + r);
System.out.println("LinkedList lookup: " + startLinked + " to " + stopLinked + " took " + (stopLinked.getTime() - startLinked.getTime()));
System.out.println(" ArrayList lookup: " + startArr + " to " + stopArr + " took " + (stopArr.getTime() - startArr.getTime()));
}Gets the result:
D:\jdk1.6.0_05\bin\java -Didea.launcher.port=7540 "-Didea.launcher.bin.path=C:\Program Files\JetBrains\IntelliJ IDEA 8.0.1\bin" -Dfile.encoding=windows-1252 -classpath "D:\jdk1.6.0_05\jre\lib\charsets.jar;D:\jdk1.6.0_05\jre\lib\deploy.jar;D:\jdk1.6.0_05\jre\lib\javaws.jar;D:\jdk1.6.0_05\jre\lib\jce.jar;D:\jdk1.6.0_05\jre\lib\jsse.jar;D:\jdk1.6.0_05\jre\lib\management-agent.jar;D:\jdk1.6.0_05\jre\lib\plugin.jar;D:\jdk1.6.0_05\jre\lib\resources.jar;D:\jdk1.6.0_05\jre\lib\rt.jar;D:\jdk1.6.0_05\jre\lib\ext\dnsns.jar;D:\jdk1.6.0_05\jre\lib\ext\localedata.jar;D:\jdk1.6.0_05\jre\lib\ext\sunjce_provider.jar;D:\jdk1.6.0_05\jre\lib\ext\sunmscapi.jar;D:\jdk1.6.0_05\jre\lib\ext\sunpkcs11.jar;F:\dev\Euler\out\production\Euler;C:\Program Files\JetBrains\IntelliJ IDEA 8.0.1\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMain jtw.test.SpeedTest
Total: 499500000
Total: 499500000
LinkedList iteration: Wed Jan 21 07:32:41 CET 2009 to Wed Jan 21 07:32:41 CET 2009 took 30
ArrayList iteration: Wed Jan 21 07:32:41 CET 2009 to Wed Jan 21 07:32:41 CET 2009 took 53
Total: 499500000
Total: 499500000
LinkedList lookup: Wed Jan 21 07:32:41 CET 2009 to Wed Jan 21 07:32:42 CET 2009 took 424
ArrayList lookup: Wed Jan 21 07:32:42 CET 2009 to Wed Jan 21 07:32:42 CET 2009 took 22
Process finished with exit code 0Given the internal representation of the datatypes, this is to be expected. -
Differece between ArrayList and LinkedList
Differece between ArrayList and LinkedList
An array list is implemented as an array. A LinkedList is implemented as a series of separate nodes linked by references.
Although they both support the same methods, that has performance implications. Linked lists are better at inserting and deleting arbitary elements, but are slow to reference an element by index. -
A suggestion : use "loop array list" instead of ArrayList / LinkedList
ArrayList is good at:
get / set by index : O(1)
appending : O(log(n))
remove last : O(1)
and very bad at:
add middle : O(n)
remove from middle : O(n)
LinkedList is good at:
fast remove from middle, if your iteraror already goes there : O(1)
convenient methods : addFirst, addLast, removeFirst, removeLast : O(1)
and very bad at :
get / set by index : O(n)
here I want to make a suggestion : use "loop array list" instead of the ArrayList and LinkedList.
a "loop array list" is based on array, just like ArrayList. But it has 2 member-variables : the start position, and the real size. the start position can be anywhere within array.length. an element of index "i" is stored in array[ start + i ], and when (start + i > array.length), loop to the beginning of the array; when (start + i < 0), loop to the end of the array.
this "loop array list" has all the good sides:
get / set by index : O(1)
add first / last : O(log(n))
remove first / last : O(log(n))
add / remove from middle : O(n)
(note : because we shrink the backup-array when the real size is too small, add / remove operation take O(log(n)) now.)
the only problem is : add / remove from middle. let's take a look at it.
1. the LinkedList does NOT really add/remove from middle in O(1), you has to locate the element, which is O(n).
2. O(n) is acceptable, O(n^2) is not acceptable. try this : keep removing first element from an very big ArrayList ( size>10^6 ) until it's empty.
the fact is, any list can perform batch-remove / batch-add operation in O(n) instead of O(n^2). it's easy : allocate a new list, iterate the original list, copy the element into the new list if condition is satisfied.
so, instead of "remove from middle", what we need is a new methods : removeAllByCondition( Condition condition ), and now the batch-remove operation can be done in O(n)
here is an implementation of mine. I've tested it on my computer( 512mem + 2G cpu, win2k + jdk1.5 ), it's amazing, just a little slower then ArrayList when add last, and a liitle slower then LinkedList when batch-remove. in all other cases, it's far more better then those 2 kinds of List.
// source code : List2
import java.util.AbstractList;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Set;
public final class List2<T> extends AbstractList<T> {
private static int initialArrayLength = 4;
private T[] array;
private int start;
private int size;
private void init( T[] newArray, int start_a, int size_a ) {
array = newArray;
start = start_a;
size = size_a;
@SuppressWarnings("unchecked")
private void init() {
init( (T[]) new Object[ initialArrayLength ], 0, 0 );
public List2() {
init();
@SuppressWarnings("unchecked")
public List2( Collection<? extends T> collection ) {
init(
collection.toArray( (T[]) new Object[ collection.size() * 11 / 10 + 1 ] ),
0,
collection.size()
private List2( T[] array_a, int start_a, int size_a ) {
init( array_a, start_a, size_a );
@SuppressWarnings("unchecked")
public static <TT> List2<TT> createV( TT... elements ) {
TT[] array = (TT[]) new Object[ elements.length * 11 / 10 + 1 ];
System.arraycopy( elements, 0, array, 0, elements.length );
return new List2<TT>( array, 0, elements.length );
public static List2<Double> create( double... elements ) {
Double[] array = new Double[ elements.length * 11 / 10 + 1 ];
for( int i=0; i < elements.length; i++ )
array[i] = elements;
return new List2<Double>( array, 0, elements.length );
public static List2<Integer> create( int... elements ) {
Integer[] array2 = new Integer[ elements.length * 11 / 10 + 1 ];
for( int i=0; i < elements.length; i++ )
array2[i] = elements[i];
return new List2<Integer>( array2, 0, elements.length );
public static List2<Character> create( char... elements ) {
Character[] array2 = new Character[ elements.length * 11 / 10 + 1 ];
for( int i=0; i < elements.length; i++ )
array2[i] = elements[i];
return new List2<Character>( array2, 0, elements.length );
public static List2<Character> create( String s ) {
return create( s.toCharArray() );
public List2<T> clone() {
return new List2<T>( this );
// basic
public int size() {
return size;
private int index( int index ) {
int i = start + index;
if( i >= array.length )
i -= array.length;
return i;
public T get( int d ) {
if( d < 0 || d >= size )
throw new IndexOutOfBoundsException();
if( size == 0 )
throw new NoSuchElementException();
return array[ index( d ) ];
public T set( int index, T element ) {
if( index < 0 || index >= size )
throw new IndexOutOfBoundsException();
int i = index( index );
T oldElement = array[i];
array[i] = element;
return oldElement;
@SuppressWarnings("unchecked")
private void copyAndSetToNewArray( int newArrayLength ) {
T[] newArray = (T[]) new Object[ newArrayLength ];
for( int i=0; i<size; i++ )
newArray[i] = array[ index( i ) ];
init( newArray, 0, size );
public void addFirst( T element ) {
if( size == array.length )
copyAndSetToNewArray( size * 3 / 2 + 1 );
int i = index( array.length - 1 );
array[ i ] = element;
start = i;
size++;
public void addLast( T element ) {
if( size == array.length )
copyAndSetToNewArray( size * 3 / 2 + 1 );
array[ index( size ) ] = element;
size++;
public T removeFirst() {
if( size == 0 )
throw new NoSuchElementException();
T oldElement = array[ start ];
array[ start ] = null;
start = index( 1 );
size--;
if( array.length > size * 2 + 1 )
copyAndSetToNewArray( size * 11 / 10 + 1 );
return oldElement;
public T removeLast() {
if( size == 0 )
throw new NoSuchElementException();
int i = index( size - 1 );
T oldElement = array[i];
array[i] = null;
size--;
if( array.length > size * 2 + 1 )
copyAndSetToNewArray( size * 11 / 10 + 1 );
return oldElement;
@SuppressWarnings("unchecked")
public int removeAll( ListCondition<T> condition ) {
T[] newArray = (T[]) new Object[ array.length ];
int iNew = 0;
for( int i=0; i < size; i++ ) {
T element = get( i );
if( ! condition.isConditionSatisfied( this, i, element ) )
newArray[ iNew++ ] = element;
int oldSize = size;
init( newArray, 0, iNew );
if( array.length > size * 2 + 1 )
copyAndSetToNewArray( size * 11 / 10 + 1 );
return size - oldSize;
// aux
public boolean equals(Object obj) {
if( obj == this )
return true;
if( obj instanceof List2 ) {
List2 that = (List2) obj;
if( this.size != that.size )
return false;
for( int i=0; i < size; i++ )
if( ! Tools.equals( this.array[ this.index(i) ], that.array[ that.index(i) ] ) )
return false;
return true;
if( obj instanceof List ) {
List that = (List) obj;
if( this.size != that.size() )
return false;
Iterator thatIter = that.iterator();
for( int i=0; i < size; i++ )
if( ! Tools.equals( this.array[ this.index(i) ], thatIter.next() ) )
return false;
return true;
return true;
public int hashCode() {
int hashCode = 1;
for( int i=0; i < size; i++ ) {
T element = array[ index( i ) ];
hashCode = 31*hashCode + ( element==null ? 0 : element.hashCode() );
return hashCode;
public boolean isEmpty() {
return size == 0;
public T getFirst() {
return get( 0 );
public T getLast() {
return get( size() - 1 );
public T getRandom() {
return get( (int) (Math.random() * size) );
public int indexOf( Object element ) {
for( int i=0; i < size; i++ )
if( Tools.equals( array[ index( i ) ], element ) )
return i;
return -1;
public int lastIndexOf( Object element ) {
for( int i=size-1; i >= 0; i-- )
if( Tools.equals( array[ index( i ) ], element ) )
return i;
return -1;
public boolean contains( Object element ) {
return indexOf( element ) != -1;
public boolean add( T element ) {
addLast( element );
return true;
@Deprecated
public void add( int index, T element ) {
throw new UnsupportedOperationException();
public T remove() {
return removeFirst();
@Deprecated
public boolean remove( Object element ) {
throw new UnsupportedOperationException( "use removeAll( Condition ) instead" );
@Deprecated
public T remove( int index ) {
throw new UnsupportedOperationException( "use removeAll( Condition ) instead" );
public void clear() {
init();
public Object[] toArray() {
Object[] result = new Object[ size ];
for( int i=0; i < size; i++ )
result[i] = array[ index( i ) ];
return result;
@SuppressWarnings("unchecked")
public <TT> TT[] toArray( TT[] a ) {
if( a.length < size )
a = (TT[]) java.lang.reflect.Array.newInstance( a.getClass().getComponentType(), size );
for( int i=0; i < size; i++ )
a[i] = (TT) array[ index( i ) ];
if( a.length > size )
a[size] = null;
return a;
@SuppressWarnings("unchecked")
public void sort() {
Object[] a = toArray();
Arrays.sort( a );
for( int i=0; i < size; i++ )
array[ i ] = (T) a[ i ];
start = 0;
@SuppressWarnings("unchecked")
public void sortDesc() {
Object[] a = toArray();
Arrays.sort( a );
for( int i=0, j=size-1; i < size; i++, j-- )
array[ i ] = (T) a[ j ];
start = 0;
@SuppressWarnings("unchecked")
public void sort( Comparator<T> comparator ) {
T[] a = (T[]) toArray();
Arrays.sort( a, comparator );
for( int i=0; i < size; i++ )
array[ i ] = a[ i ];
start = 0;
@SuppressWarnings("unchecked")
public void sortDesc( Comparator<T> comparator ) {
T[] a = (T[]) toArray();
Arrays.sort( a, comparator );
for( int i=0, j=size-1; i < size; i++, j-- )
array[ i ] = a[ j ];
start = 0;
public String toString( String delimiter ) {
return toString( "", delimiter, "", size() );
public String toString( String prefix, String delimiter, String suffix, int max ) {
StringBuffer stringBuffer = new StringBuffer( prefix );
int dest = Math.min( max, size );
for( int i=0; i < dest; i++ ) {
stringBuffer.append( get(i) );
if( i < dest - 1 )
stringBuffer.append( delimiter );
if( size > max )
stringBuffer.append( "...(" ).append( size() - max ).append( " more)" );
stringBuffer.append( suffix );
return stringBuffer.toString();
// batch operation
public boolean containsAll( Collection<?> that ) {
Set<Object> thisSet = new HashSet<Object>( this );
for( Object element : that )
if( ! thisSet.contains( element ) )
return false;
return true;
@SuppressWarnings("unchecked")
public List2<T> subList( int fromIndex, int toIndex ) {
if( fromIndex < 0 || toIndex > size || toIndex < fromIndex )
throw new IndexOutOfBoundsException();
int newSize = toIndex - fromIndex;
T[] newArray = (T[]) new Object[ newSize * 11 / 10 + 1 ];
for( int i=fromIndex, iNew=0; i < toIndex; i++, iNew++ )
newArray[ iNew ] = array[ index( i ) ];
return new List2<T>( newArray, 0, newSize );
public void addV( T... that ) {
for( T element : that )
addLast( element );
public boolean addAll( Collection<? extends T> that ) {
for( T element : that )
addLast( element );
return ! that.isEmpty();
@Deprecated
public boolean addAll( int index, Collection<? extends T> c ) {
throw new UnsupportedOperationException();
public void removeRest( T element ) {
int position = lastIndexOf( element );
if( position == -1 )
return;
while( ! Tools.equals( element, removeLast() ) );
public void removeAllEquals( final T element ) {
removeAll( new ListCondition<T>() { public boolean isConditionSatisfied(List2 list, int index, T currentElement) {
return currentElement.equals( element );
public void removeAllBetween( final T from, final T to ) {
removeAll( new ListCondition<T>() {
@SuppressWarnings("unchecked")
public boolean isConditionSatisfied(List2 list, int index, T element) {
if( from != null && ((Comparable) from).compareTo( element ) > 0 )
return false;
if( to != null && ((Comparable) to).compareTo( element ) <= 0 )
return false;
return true;
public boolean retainAll( Collection<?> that ) {
final Set<Object> thatSet = new HashSet<Object>( that );
int removeCount = removeAll( new ListCondition<T>() { public boolean isConditionSatisfied(List2 list, int index, T element) {
return ! thatSet.contains( element );
return removeCount > 0;
public boolean removeAll( Collection<?> that ) {
final Set<Object> thatSet = new HashSet<Object>( that );
int removeCount = removeAll( new ListCondition<T>() { public boolean isConditionSatisfied(List2 list, int index, T element) {
return thatSet.contains( element );
return removeCount > 0;
// unit test
private static int maxTestCount = 1000 * 1000;
public static void unitTest() throws Exception {
// thest thoese methods for one time
Tools.ensureEquals( new List2(), new ArrayList() );
Tools.ensureNotEquals( List2.create( "abcde" ), new ArrayList() );
Tools.ensureNotEquals( List2.create( "abcde" ), List2.create( "abcdef" ) );
final List<Double> list1 = new ArrayList<Double>();
final List2<Double> list2 = new List2<Double>();
Runnable[] tasks = new Runnable[] {
// test those methods that do NOT change the list
new Runnable() { public void run() {
Tools.ensureEquals( new List2<Double>( list1 ), list1 );
Tools.ensureEquals( List2.createV( list1.toArray() ), list1 );
Tools.ensureEquals( List2.createV( list1.toArray( new Double[0] ) ), list1 );
double[] doubles = new double[ list1.size() ];
int i = 0;
for( double d : list1 )
doubles[i++] = d;
Tools.ensureEquals( List2.create( doubles ), list1 );
Tools.ensure( list1.isEmpty() == list2.isEmpty() );
Arrays.equals( list1.toArray(), list2.toArray() );
Tools.ensureEquals( list1, list2.clone() );
Double notExistElement = -2.0;
Tools.ensure( list1.indexOf( notExistElement ) == -1 );
Tools.ensure( list1.lastIndexOf( notExistElement ) == -1 );
Tools.ensure( list1.contains( notExistElement ) == false );
Tools.ensureEquals( list1.toString(), list2.toString() );
Tools.ensureEquals( list1.toString(), list2.toString() );
Tools.ensureEquals( list1.hashCode(), list2.hashCode() );
if( list1.isEmpty() )
return;
Tools.ensure( list1.get(0).equals( list2.getFirst() ) );
Tools.ensure( list1.get(list1.size()-1).equals( list2.getLast() ) );
Double existRandomElement = list2.getRandom();
Tools.ensure( list1.contains( existRandomElement ) );
Tools.ensure( list2.contains( existRandomElement ) );
Tools.ensure( list1.indexOf( existRandomElement ) == list2.indexOf( existRandomElement ) );
Tools.ensure( list1.indexOf( existRandomElement ) == list2.indexOf( existRandomElement ) );
int from = (int) (Math.random() * list1.size());
int to = (int) (Math.random() * (list1.size()+1));
if( from > to ) {
int t = from;
from = to;
to = t;
Tools.ensureEquals( list1.subList( from, to ), list2.subList( from, to ) );
// test those methods that change the list
new Runnable() { public void run() {
if( list1.isEmpty() )
return;
int i = (int) (Math.random() * list1.size());
double d = Math.random();
list1.set( i, d );
list2.set( i, d );
new Runnable() { public void run() {
if( list1.isEmpty() )
return;
int i = (int) (Math.random() * list1.size());
Tools.ensure( list1.get( i ).equals( list2.get( i ) ) );
new Runnable() { public void run() {
double d = Math.random();
list1.add( 0, d );
list2.addFirst( d );
new Runnable() { public void run() {
double d = Math.random();
list1.add( d );
list2.addLast( d );
new Runnable() { public void run() {
double d = Math.random();
list1.add( d );
list2.addLast( d );
new Runnable() { public void run() {
if( list1.isEmpty() )
return;
Tools.ensure( list1.remove( 0 ).equals( list2.removeFirst() ) );
new Runnable() { public void run() {
if( list1.isEmpty() )
return;
Tools.ensure( list1.remove( list1.size() - 1 ).equals( list2.removeLast() ) );
new Runnable() { public void run() {
if( list1.isEmpty() )
return;
int i = 0;
for( Iterator<Double> iter=list1.iterator(); iter.hasNext(); i++ ) {
iter.next();
if( i % 3 == 0 )
iter.remove();
list2.removeAll( new ListCondition<Double>() { public boolean isConditionSatisfied(List2 list, int index, Double element) {
return index % 3 == 0;
new Runnable() { public void run() {
double d = Math.random();
list1.add( d );
list2.add( d );
new Runnable() { public void run() {
if( list1.isEmpty() )
return;
Tools.ensure( list1.remove(0).equals( list2.remove() ) );
new Runnable() { public void run() {
if( list1.isEmpty() )
return;
int r = (int) (Math.random() * list1.size());
Double element = list1.get( r );
int index = list1.lastIndexOf( element );
for( int i=list1.size()-1; i>=index; i-- )
list1.remove( i );
list2.removeRest( element );
new Runnable() { public void run() {
list2.removeRest( Math.random() - 2 );
new Runnable() { public void run() {
list1.clear();
list2.clear();
new Runnable() { public void run() {
Collections.sort( list1 );
list2.sort();
new Runnable() { public void run() {
Collections.sort( list1 );
Collections.reverse( list1 );
list2.sortDesc();
new Runnable() { public void run() {
Comparator<Double> comparator = new Comparator<Double>() { public int compare(Double o1, Double o2) {
return o1.toString().substring(2).compareTo( o2.toString().substring(2) );
Collections.sort( list1, comparator );
list2.sort( comparator );
new Runnable() { public void run() {
Comparator<Double> comparator = new Comparator<Double>() { public int compare(Double o1, Double o2) {
return o1.toString().substring(2).compareTo( o2.toString().substring(2) );
Collections.sort( list1, comparator );
Collections.reverse( list1 );
list2.sortDesc( comparator );
new Runnable() { public void run() {
Double notExistElement = -2.0;
list2.removeAllEquals( notExistElement );
Tools.ensureEquals( list1, list2 );
list2.removeAllBetween( 0.5, 0.6 );
for( Iterator<Double> iter=list1.iterator(); iter.hasNext(); ) {
double d = iter.next();
if( d >= 0.5 && d < 0.6 )
iter.remove();
Tools.ensureEquals( list1, list2 );
System.out.print( "test List2 " );
for( int i=0; i < maxTestCount; i++ ) {
tasks[ (int) (Math.random() * tasks.length) ].run();
Tools.ensureEquals( list1, list2 );
if( i % (maxTestCount/10) == 0 )
System.out.print( "." );
System.out.println( " ok" );
// source code : ListCondition
public interface ListCondition<T> {
boolean isConditionSatisfied( List2 list, int index, T element );Hi,
I have the following statement:
private List list = new ArrayList();
why not use private ArrayList list = new
ArrayList()?
I know ArrayList implements List, so list has a wide
scope, right? What's the benefit?
Thanks,
JieBy using the interface you are not tied to a specific implementation.
Later, you may determine that using a LinkedList is more efficient to your specific code and then all you need to do is change the statement to:
private List list = new LinkedList();As long as you are not casting the list reference to ArrayList (or something along those lines) you would not need to change anything else. -
Understanding method implementation for LinkedList class
Hello
I'm new to java and just trying to get my head around data structures, particularly ArrayList and LinkedList implementations. I've looked at the Sun API for both classes, but would like to see how the methods are implmented so I can venture into writing my own versions of these classes..
Does anyone know if there is a resource showing the full method implementation so I can view how they work?
thanks,a really strange licence: look but don't touch, and it's still under copyrightThis license seems to make sense: you can look at it and learn from it but you are not supposed to make an own, incomptabile version.
-
I wrote an ArrayList that contained some LinkedLists. I wrote that ArrayList to a txt file. It looks like this in the text file:
[[CLAY, CLAY, CLAY, CLAY, CLAY, CLAY, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, SAND, SAND, SAND, SAND, SAND, SAND], [***], [SILT, SILT, SILT, SILT, SILT, SILT, SILT, SILT, SILT, SILT, SILT, SILT], [***], [***], [LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM], [***], [***], [***], [***]]
Now I'm having a hard time figuring out exactly how to get it back. I've started by creating a buffered reader but now I'm not sure if that was right. I guess the main thing throwing me off is the [ ]'s. How can I split this and get an ArrayList like:
[CLAY, CLAY, CLAY, CLAY, CLAY, CLAY, LOAM, LOAM, LOAM, LOAM, LOAM, LOAM, SAND, SAND, SAND, SAND, SAND, SAND]
[SILT, SILT, SILT, SILT, SILT, SILT, SILT, SILT, SILT, SILT, SILT, SILT]
BufferedReader br;
ArrayList loadSoil = new ArrayList();
try {
br = new BufferedReader( new FileReader(System.getProperties().getProperty("user.home")+ "/CMIM/CEValues.CED"));
String fileLine = br.readLine();
while(fileLine != null) {}Sorry, I'm pretty new to the whole I/O thing in Java. I tried looking up some other answers but didn't find one for an ArrayList containing LinkedLists.Sch104 wrote:
Well I changed my write method to:[snip]
It is now telling me I can't write an ArrayList<LinkedList>.You need to call the writeObject method, not the write method. The following code:
import java.io.*;
import java.util.*;
public class WriteObjectTest {
public static void main(String[] args) throws Exception {
ArrayList<LinkedList<String>> CETotalCover = new ArrayList<LinkedList<String>>();
LinkedList<String> stuff = new LinkedList<String>();
stuff.add("Stuff");
stuff.add("More Stuff");
CETotalCover.add(stuff);
File CEValues = new File(System.getProperties().getProperty("user.home"),
"/CMIM/CEValues.CED");
try {
ObjectOutputStream os = new ObjectOutputStream( new BufferedOutputStream
( new FileOutputStream (CEValues)));
os.writeObject(CETotalCover);
os.close();
} catch (FileNotFoundException e2) {
// TODO Auto-generated catch block
e2.printStackTrace();
} catch (IOException e2) {
// TODO Auto-generated catch block
e2.printStackTrace();
ArrayList list = null;
FileInputStream fis = new FileInputStream(CEValues);
ObjectInputStream ois = new ObjectInputStream(fis);
list = (ArrayList<LinkedList<String>>) ois.readObject();
ois.close();
System.out.println(list);
}Produced the following output:
$java WriteObjectTest
[[Stuff, More Stuff]]
Note: Try to use standard java naming conventions and camel-case your variable names, starting with a lower-case letter.
Good Luck
Lee -
If I wanna sort my arraylist, can I make it???How?
Thanx!Do you know how to use interfaces? Do you understand OOP and Java? Once nice thing about using generic types like an interface, is that you can easily switch out different algorithms. For example, if you are doing something like this:
ArrayList myList = new ArrayList();
and throughout your code you have methods like:
public void doSomething(ArrayList list)
you limit youself to using nothing but ArrayLists. What happens if your code suddenly is used by more than one concurrent person? You will no doubt run into mult-threading issues using an ArrayList. However, Vector, which is identical to an ArrayList but is thread-safe, can be swapped for an ArrayList with no changes to your code. You MUST use the methods defined in the interface however, when working on the ArrayList or Vector. As an example, there are times when you may want to "speed up" your code. When using a Vector, you lose a lot of speed because a Vector has a lot of syncronized overhead in it. This is to ensure that multiple threads do not lock or cause any problems while accessing the same Vector in memory. At times, you may find out that a certain Vector is NEVER accessed by more than one thread. Therefore, its a perfect candidate for turning into an ArrayList, as the ArrayList has no synchronized overhead and is thus much faster. But, if you are not using the List interface methods, you may find you need to change a lot more code for this to work.
List is an interface (java.util.List) that defines methods like add, remove, get, and so on. As the other replier said, you can use the Collection framework to sort a list, and do other things with it. If you use a Vector ad usee addElement(), removeElement, etc, they wont work with ArrayList or LinkedList. The List interface is implemented by ArrayList, Vector and LinkedList. Each has their benefits. For example, if you write a program using a Vector, and it does a LOT of moving items back and forth (such as sorting), a LinkedList will be faster because the way they work, they just move a pointer to move the entire contents of the list. A Vector and ArrayList have to copy the data. However, searching is done much faster on Vectors and ArrayLists. So if you need to do a lot of searching, then one of those two would be better. If you need to do all three (or more), then you need to experiment. The nice thing is, as long as you use the List interface everywhere (except when instantiating the objects), you can simply do a find/replace in your code to replace ArrayList with Vector or LinkedList and you are all set.
Hope that helps. -
A getName method allways returns null, why?
I have an
ArrayList<Animals> array_list = new ArrayList<Animals>();
LinkedList<Animals> linked_list = new LinkedList<Animals>();
I want the getName() method in class NewListener to be accessed from the class NextListener which extends NewListener, and therefor should get access to the method. But when I run the program, it allways returns null. Why?
class NewListener implements ActionListener
public String name;
public void actionPerformed(ActionEvent e)
String str_name = showInputDialog(this,"Animal name: ",null);
if(str_name == null)
return;
for(int i=0; i<array_list.size(); i++)
if(array_list.get(i).getName().equalsIgnoreCase(str_name))
setName(str_name); // set the name with the setName() method
linked_list.add(array_list.get(i));
public void setName(String name)
this.name=name;
public String getName()
return name; // this line returns "null"
// return "Hello"; // this line works and returns "Hello"
class NextListener extends NewListener implements ActionListener
public void actionPerformed(ActionEvent e)
try
linked_list .removeFirst();
}catch(NoSuchElementException er)
System.out.println("Numerical value");
String info = getName()+" is in line"; // Why does the getName() method in the NewListener allways return a null?
showMessageDialog(this, info, "Notice", INFORMATION_MESSAGE);
}{code}Roxxor wrote:
Ok, I changed the name to private and I also tried with
public void setName(String name)
System.out.println("setting name on " + this + " to " + name); // <--- ADD THIS LINE
this.name=name;
}and it works. So this.name SHOULD get the value of name, but it doesn�t.
So the question is: why does getName() return null?Your code is doing exactly what you're telling it to do. One or more of your assumptions is wrong. Keep digging. Add more print statements.
Above all, you must drop the attitude that "it should work." There's a bug in your code. You have to find it. Repeating the mantra "It should work" is simply going to put blinders on and make it almost impossible to find your error. Instead, you have to think, "What did I do wrong?" and "If getName is returning null, then setName was never called or was called with null." -
Hey,
My program collects 5 pieces of information per object from user. Some of the input data is in String format, rest are Integers. I create an object from this data and put in into a table. My table contains max 10 pieces of information.
I have editing options for this data, which are erase one or all pieces, or modify a piece. I erase data by simply setting the index to null. Erasing one piece is incomplete atm, here's why:
Say I have 5 pieces in table, and I erase the one with index of 0. I can't print my information because the table starts with a null value:
int index = 0;
if (table[index] != null) { System.out.println(data);} ..
My guess is that I can solve this problem by decreasing the index of pieces greater than the modified one by 1. I can imagine that I'll be using for loop here. This is where I run out of ideas: is it possible to just modify the index, or do I have to rewrite the data again?
Any help is appreciated,
br,
nomiI think using for loop would be the easiest way (?).
I'm filling the table as simply as:
items[index] = new table (value, quality..);Using LinkedList seems a bit far fetched for me. But
again, if I am to use for loop, I think I would have
to rewrite the data to appropriate index?Why is a List far fetched? Type of List you pick depends on how you use the list (whether you want RandomAccess, etc.).
List items = new ArrayList(); // or LinkedList
items.remove(index); // Remove the item at index.To use an array:
Table [] items = new Table[20]; // whatever size
items[index] = new Table(value, quality, ...);
// To remove:
System.arraycopy(items, index, items, index+1, items.length-(index+1));
items[items.length-1] = null; -
Need suggestion for variable size array of primitive type.
Hi all,
I am working on a problem in which I need to keep an array of primitive (type int) sorted. Also I insert new elements while keeping it sorted, and at times I merge two similar arrays with unique elements.
I would welcome suggestions on the implementation aspects as to which type/class to use. My primary consideration is performance. Here are my observations:
1. type int
Efficient operation, but arrays are fixed size so it makes clumsy code and overhead when the array is expanded or merged with another.
Methods in class Arrays can be used, incl. binary search and sort.
2. Vector, ArrayList, List, LinkedList
Accept objects only. I can use Integer instead of int, but it will involve overhead, and I'll need to write my own sort and search routines (already done).
For now, I choose option 2 using Vectors. Is there a better choice, or are there other options, given the conditions and consideration enumerated at the beginning?
Appreciate any input or comments.mathmate wrote:
I have not had the occasion to use them in parallel to recognize the difference. It pays to talk to people!A small benchmark is easily constructed:
import bak.pcj.list.IntArrayList;
import java.util.Random;
import java.util.ArrayList;
public class CollectionTest {
static void testObjectsList(ArrayList<Integer> list, int n, long seed) {
long start = System.currentTimeMillis();
Random rand = new Random(seed);
for(int i = 0; i < n; i++)
list.add(new Integer(rand.nextInt()));
for(int i = 0; i < n/2; i++)
list.remove(rand.nextInt(list.size()));
long end = System.currentTimeMillis();
System.out.println("objectsList -> "+(end-start)+" ms.");
static void testPrimitiveList(IntArrayList list, int n, long seed) {
long start = System.currentTimeMillis();
Random rand = new Random(seed);
for(int i = 0; i < n; i++)
list.add(rand.nextInt());
for(int i = 0; i < n/2; i++)
list.remove(rand.nextInt(list.size()));
long end = System.currentTimeMillis();
System.out.println("primitiveList -> "+(end-start)+" ms.");
public static void main(String[] args) {
long seed = System.currentTimeMillis();
int numTests = 100000;
testObjectsList(new ArrayList<Integer>(), numTests, seed);
testPrimitiveList(new IntArrayList(), numTests, seed);
}In the test above, Java's ArrayList is about 5 times faster. But when commenting out the remove(...) methods, the primitive 3rd party IntArrayList is about 4 to 5 times faster.
Give it a spin.
Again: just try to do it with the standard classes: if performance lacks, look at something else. -
A List on the pageFlow in a portlet (8.1)
When I put a java.util.List on the pageFlow, workshop complains that it's
not Serializable.
The annoying this is that the log also reports this warning.
Is it possible to make weblogic ignore this and only this warning?
My business tier's session bean returns a java.util.List.
Should I put the list on the request otherwise?
Thank you for any and all help,
GeoffreyI delibratly want to use the List interface, this way I stay implementation
independ.
My bean now returns an ArrayList but if at some point I want to use a
LinkedList, it will be a very small adjustment.
This is the entire point of the Collections API.
You can't be sure that an ArrayList doesn't contain no Serializable items
anyway.
So option 1 and 3 are out.
I found a much faster way than option 2: Just put it in the request and pick
it up in the jsp (this works fine as long as you don't need forms).
In any case: the entire PageFlow framework doesn't feel good, for various
reasons, it seems to limit your abilities.
Please take a look at my next post: "netui:form and ..."
Thank you for any and all help,
Geoffrey
"Gregory Smith" <[email protected]> schreef in bericht
news:[email protected]...
That's because the java.util.List interface doesn't extend Serializable.
However, the 2 normally used implementations, ArrayList and LinkedList,
do implement Serializable. And, the java pageflow compiler only knows
that it's a List and that FlowControllers are supposed to be
Serializable and have only Serializable non-transient variables.
I'm not sure if there's a way to make it ignore this warning, but youcould:
1. Have the session bean return a LinkedList or ArrayList and declare
that as the pageflow variable type, or
2. Create a subinterface of java.util.List called SerializableList that
also extends Serializable. Make a subclasses of LinkedList and/or
ArrayList that just implements SerializableList or make the List class
your EJB returns implement SerializableList, and use SerializableList on
the session bean interface and the pageflow variable, or
3. Declare the pageflow variable as a ArrayList, and convert the List
from the session bean an ArrayList, e.g.:
if (listFromEJB instanceof ArrayList)
this.pfList = (ArrayList)listFromEJB;
else
this.pfList = new ArrayList(listFromEJB);
Not perfect, but some ideas.
Greg
Geoffrey wrote:
When I put a java.util.List on the pageFlow, workshop complains that
it's
not Serializable.
The annoying this is that the log also reports this warning.
Is it possible to make weblogic ignore this and only this warning?
My business tier's session bean returns a java.util.List.
Should I put the list on the request otherwise? -
How to read a text delimited file using 2 dimentional array in java ??
hi,
I am new to java programming.. I have to do a task where in i have to read a text delimeted file in an array.. For example.. If the file is as follows
Name place Value
adi goa 20
shri mumbai 30
riya bangalr 45
I want it to be read in java so as to get an array[row][columns]
This is something i am currently upto, but cant get any further.
import java.io.BufferedReader;
import java.io.FileReader;
public class generateGML{
public static void main(String[] argv)
throws Exception{
BufferedReader fh = new BufferedReader(new FileReader("filename.txt"));
String s;
while ((s=fh.readLine())!=null){
String[] columns = s.split("\t");
String name = columns[0];
String place = columns[1];
String value = columns[2];
It reads columns,But I want it two dimentionally,as in something like matrix[row_num][column_num].
Can anyone please suggest me..You could do the following:
String[][] array = new String[rows][];
int row_num = 0;
while ((s=fh.readLine())!=null) {
array[row_num++] = s.split("\t");
}However, you need to know ahead of time how many rows to allocate. If you allocate more than needed, you'll need to copy to a new array, or you'll need to keep track of how much is actually populated. If you allocate less than needed, you'll get an ArrayIndexOutOfBoundsException.
Another (likely better) approach is:
Do you really need it as a 2-dimensional array? Can you make a List of objects that have a name, place, and value? Then you don't need to know how big of a list to allocate ahead of time, assuming you use a list that grows itself (like ArrayList or LinkedList). Your code would be much easier to read if you could say:
String name = list.get(10).getName();instead of
String name = array[10][0];
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