Array of primitives in an ArrayList
I have noted that I can add an array of primitive types to an ArrayList
int[] x = {1,2,4,1,6,7,1,1,3,1,5,0,1};
ArrayList tx = new ArrayList();
tx.add(x);
My question is how do I get the array back out of the ArrayList. The get method returns an Object but now can I cast this back into something that I can use to set another int array. The return Object is of class type "[I" but this did not help any.
I know I could re-wtite the code to use Integer objects in the original array but I'm sure there must be a quick way of getting the right values back from the ArrayList using the primtive array. Can anyone help?
I think you might get sth. wrong here. Your int array is put into the Arrylist's first element, the size of the arrylist is one, but the length of your array is 12. Look at this:int[] x = {1,2,4,1,6,7,1,1,3,1,5,0,1};
ArrayList tx = new ArrayList();
tx.add(x);
int [] y = (int [])tx.get(0);
for (int i = 0; i < y.length; i++){
System.out.println("y["+i+"] = " + y);
Similar Messages
-
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. -
How can I truncate an array of (primitive) double?
Is it like the following, or some more obviously legitimate way?
double[] dArr=new double[12345678];
dArr = Arrays.copyOf(dArr,7234567); I don't want to have both sizes allocated at the same time.
Also, (not as important to me) can I extend this array?
And this reminds me of another related question:
Why can't java allocate heap space by itself without my
having to use, e.g., -Xmx999m manually and guessingly?
Or can it?
Or am I missing some procedure?hillmi wrote:
How can I truncate an array of (primitive) double?
Is it like the following, or some more obviously legitimate way?
double[] dArr=new double[12345678];
dArr = Arrays.copyOf(dArr,7234567); I don't want to have both sizes allocated at the same time.
Also, (not as important to me) can I extend this array? Extend NO.
Make a new one YES, but both would be in memory at the same time.
You could use an ArrayList with Double, then you could extend it.
And this reminds me of another related question:
Why can't java allocate heap space by itself without my
having to use, e.g., -Xmx999m manually and guessingly? I do not believe it can. -
Array Of Primitive Type (kodo3.4)
Hello,
I want to map an array of primitive type (double[] or double[][] or...) to
a blob, so I specified the mapping this way:
<extension vendor-name="kodo" key="jdbc-field-map-name" value="blob">
<extension vendor-name="kodo" key="column" value="DATA"/>
</extension>
As I use MySQL and not to have an exception, I have added:
kodo.jdbc.DBDictionary: DriverDeserializesBlobs=false
But when I tried to refresh using kodo.jdbc.meta.MappingTool, I get:
[refresh] Exception in thread "main" kodo.util.FatalInternalException:
Cannot map "fr.ifp.reservoir.model.business.geostat.Lithotype.facies".
Check the class and make sure you are using only supported types.
[refresh] at
kodo.jdbc.meta.DynamicMappingProvider.createFieldMapping(DynamicMappingProvider.java:336)
[refresh] at
kodo.jdbc.meta.DynamicMappingProvider.getFieldMapping(DynamicMappingProvider.java:118)
[refresh] at
kodo.jdbc.meta.MappingRepository.getFieldMapping(MappingRepository.java:470)
[refresh] at
kodo.jdbc.meta.AbstractClassMapping.getFieldMapping(AbstractClassMapping.java:993)
[refresh] at
kodo.jdbc.meta.AbstractClassMapping.getFieldMapping(AbstractClassMapping.java:973)
[refresh] at
kodo.jdbc.meta.AbstractClassMapping.getMappings(AbstractClassMapping.java:939)
[refresh] at
kodo.jdbc.meta.AbstractClassMapping.getDeclaredFieldMappings(AbstractClassMapping.java:659)
[refresh] at
kodo.jdbc.meta.AbstractClassMapping.resolve(AbstractClassMapping.java:801)
[refresh] at
kodo.jdbc.meta.BaseClassMapping.resolve(BaseClassMapping.java:341)
[refresh] at
kodo.jdbc.meta.MappingRepository.resolve(MappingRepository.java:431)
[refresh] at
kodo.jdbc.meta.MappingRepository.getMapping(MappingRepository.java:349)
[refresh] at
kodo.jdbc.meta.MappingRepository.getMapping(MappingRepository.java:177)
[refresh] at kodo.jdbc.meta.MappingTool.refresh(MappingTool.java:591)
[refresh] at kodo.jdbc.meta.MappingTool.run(MappingTool.java:941)
[refresh] at kodo.jdbc.meta.MappingTool.run(MappingTool.java:879)
[refresh] at kodo.jdbc.meta.MappingTool.main(MappingTool.java:802)
Thanks for your help.
nicolasHi,
No more succes with persistence-modifier="persistent"...
My class:
public class ArrayWrapper {
private String name;
private double[] array;
public ArrayWrapper(String name, double[] array) {
this.name = name;
this.array = array;
public double[] getValues() {
return array;
public String getName() {
return name;
My metadata file:
<jdo>
<package name="model">
<class name="ArrayWrapper">
<field name="array" persistence-modifier="persistent">
<extension vendor-name="kodo" key="jdbc-field-map-name" value="blob">
<extension vendor-name="kodo" key="column" value="DATA"/>
</extension>
</field>
</class>
</package>
</jdo>
My StackTrace:
refresh-mapping:
[java] Exception in thread "main" kodo.util.FatalInternalException:
Cannot map "model.ArrayWrapper.array". Check the class and make sure you
are using only supported types.
[java] at
kodo.jdbc.meta.DynamicMappingProvider.createFieldMapping(DynamicMappingProvider.java:336)
[java] at
kodo.jdbc.meta.DynamicMappingProvider.getFieldMapping(DynamicMappingProvider.java:118)
[java] at
kodo.jdbc.meta.MappingRepository.getFieldMapping(MappingRepository.java:470)
[java] at
kodo.jdbc.meta.AbstractClassMapping.getFieldMapping(AbstractClassMapping.java:993)
[java] at
kodo.jdbc.meta.AbstractClassMapping.getFieldMapping(AbstractClassMapping.java:973)
[java] at
kodo.jdbc.meta.AbstractClassMapping.getMappings(AbstractClassMapping.java:939)
[java] at
kodo.jdbc.meta.AbstractClassMapping.getDeclaredFieldMappings(AbstractClassMapping.java:659)
[java] at
kodo.jdbc.meta.AbstractClassMapping.resolve(AbstractClassMapping.java:801)
[java] at
kodo.jdbc.meta.BaseClassMapping.resolve(BaseClassMapping.java:341)
[java] at
kodo.jdbc.meta.MappingRepository.resolve(MappingRepository.java:431)
[java] at
kodo.jdbc.meta.MappingRepository.getMapping(MappingRepository.java:349)
[java] at
kodo.jdbc.meta.MappingRepository.getMapping(MappingRepository.java:177)
[java] at kodo.jdbc.meta.MappingTool.refresh(MappingTool.java:591)
[java] at kodo.jdbc.meta.MappingTool.run(MappingTool.java:941)
[java] at kodo.jdbc.meta.MappingTool.run(MappingTool.java:879)
[java] at kodo.jdbc.meta.MappingTool.main(MappingTool.java:802) -
Does TopLink support arrays of primitive types?
Does TopLink support arrays of primitive types?
You must use a collection.
If you really wanted to you could store the data as an array and use get/set methods to convert between the array and collection, or customize your own ContainerPolicy, however arrays a very inefficent to add/remove from so TopLink only provides support for collections. -
Typecasting arrays of primitives
This code has a syntax error:char[] dog = tocStr.toCharArray();
byte[] cat = (byte[]) dog;Syntax Error:
inconvertible types
found: char[]
required: byte[]
So, I cannot use typecasting with arrays of primitive data types? Do I have to use a for loop instead, casting each primitive one-by-one?You pretty much have to do them one by one, yeah.
Edit: You have a string in the beginning. Just use
byte[] cat = tocString.getBytes();Message was edited by:
jGardner -
Sorting a String Array in alpha order (Using ArrayList)
Hello all!
I am pretty new to Java and am trying to do a, seemingly, simple task; but cannot get the syntax right. I am trying to sort an ArrayList in aplha order based off of the variable String Product. Any help would be awesome!
First Class:
//This program stores all of the variables for use in Inventory.java
public class Vars {
// defining all variables
private String product;
private String prodCode;
private double price;
private double invCount;
// Begin listing getters for class
public Vars(String product) {
this.product = product;
public String getProdCode() {
return prodCode;
public String getProduct() {
return product;
public double getPrice() {
return price;
public double getInvCount() {
return invCount;
// Declaring the total variable
public double total() {
return invCount * price;
// Begin listing setters for variables
public void setProduct(String product) {
this.product = product;
public void setProdCode(String prodCode) {
this.prodCode = prodCode;
public void setInvCount(double invCount) {
this.invCount = invCount;
public void setPrice(double price) {
this.price = price;
Second Class:
//This program will use the variables stored in Vars.java
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class Inventory {
public static void main(String args[]) {
Scanner input = new Scanner(System.in);
//defining and declaring local variables
String exit;
int counter;
double gtotal;
exit = "exit";
counter = 0;
gtotal = 0;
//beginning message and beginning of the loop
System.out.print("Welcome to the Inventory Contol System\nPlease enter the Product name: ");
System.out.println();
System.out.println("When finished entering in the data, please enter EXIT in place of Product name.");
String name = input.next();
List<Vars> var = new ArrayList<Vars>(); //creating arraylist object
//loop while exit is not entered, exit loop once exit is typed into product variable
while (name.compareToIgnoreCase(exit) != 0) {
Vars vars = new Vars(name); //calling Vars methods
counter = counter ++;
System.out.println("Please enter the Product Code: ");
vars.setProdCode(input.next());
System.out.println("Inventory Count: ");
vars.setInvCount(input.nextDouble());
//Making sure that the value entered is a positive one
if(vars.getInvCount() < 0){
System.out.println("Please enter a positive number: ");
vars.setInvCount(input.nextDouble());
System.out.println("Price per product:");
vars.setPrice(input.nextDouble());
//Making sure that the value entered is a positive one
if(vars.getPrice() < 0) {
System.out.println("Please enter a positive number: ");
vars.setPrice(input.nextDouble());
System.out.println("Please enter the next Product name, or enter EXIT: ");
name = input.next();
gtotal += vars.total(); //calculation for Grand Total of all products entered
var.add(vars);
static void slectionSort(int[] product) {
for (int lastPlace = product.length-1; lastPlace > 0; lastPlace--) {
int maxLoc = 0;
for (int j = 1; j <= lastPlace; j++) {
if (product[j] > product[maxLoc]) {
maxLoc = j;
int temp = product[maxLoc];
product[maxLoc] = product[lastPlace];
product[lastPlace] = temp;
//Sorting loop function will go here, before the information is displayed
//Exit message and array list headers
System.out.print("Thank you for using the Inventory program.\nHave a wonderful day.\n");
System.out.printf("Code\tProduct\tCount\tPrice\tTotal\n");
System.out.println();
//For loop to display all entries via an ArrayList
for (Vars vars : var) {
System.out.printf("%5s\t%5s\t%.01f\t$%.02f\t$%.02f\n\n", vars.getProdCode(),
vars.getProduct(), vars.getInvCount(), vars.getPrice(),vars.total());
//Displays the amount of entries made and Grand Total of all products entered
System.out.println();
System.out.printf("The number of products entered is %d\n", var.size());
System.out.printf("The Grand Total cost for the products entered is $ %s\n", gtotal);
System.out.println();
}go through below links, you can easily understand how to sort lists.
http://www.onjava.com/lpt/a/3286
http://java.sun.com/docs/books/tutorial/collections/interfaces/order.html
http://www.javaworld.com/javaworld/jw-12-2002/jw-1227-sort.html -
Configure array of primitive type for POF
My impression is that Coherence's POF implementation can handle Java primitive and String by default thus we don't need to provide a customized POF configuration file if the object been put into the cache is Java primitive type.
How about arrary of primitive type? For example, byte[]. Can Coherence's POF implementation handle byte[] as well?Just asking since we plan to move from using Externalizable to POF and not sure if we need special handling for byte[] type.
Thanks for the reply.
Regards,
Chen -
<< This message (by a_silent_lamb) yanked from another thread which had gotten hopelessly off-topic. >>
Auto-unboxing:
According to
http://java.sun.com/features/2003/05/bloch_qa.html
JSR-201 has not yet decided how to auto-unbox null.
Any opinion?
My opinion is to throw NullPointerException as perhaps
it is much more consistent to how Java is currently
doing.I think this is an important question. I tend to agree that it should throw an exception, for two reasons:
(1) As the OP said, it's what experienced Java developers will expect to happen.
(2) As Bloch said, automatically converting null objects to default primitive values would permit subtle runtime errors to creep in.
It seems to me that, if you expect the value to be something that can be auto-unboxed, it's your responsibility to ensure that it never becomes null in the first place. Using null to represent a default value is sloppy programming anyway.
But maybe that's just a conservative reflex on my part. After all, JSR-201 and JSR-14 are all about relieving the developer of the burden of writing the same boilerplate code over and over. What's the use of eliminating type checking and casting, only to force developers to check for nulls before auto-unboxing?
I've also been wondering what the default values would be for the various primitive wrapper classes. For the integral types, the obvious answer is zero, and for Booleans, false. But would null Floats and Doubles convert to 0.0, or NaN? And what about Characters?Imagine if you switched some of your
code from using an array of primitives to an
ArrayList. If autounboxing null results in a
NullPointerException, you'll have to go through all
your code and insert null checks to avoid exceptions.
With the default value instead, you won't have to
rewrite that code.If you switched your primitive array to an ArrayList without auto-(un)boxing, you'd still have to check for null. Using auto-unboxing to ignore nulls that you'd have to handle anyway is lazy programming.
Your OOP solution in this case is not to ignore nulls, but to extend ArrayList to not allow null entries, something like:public class NulllessArrayList extends Arraylist
public void add (Object obj)
if (obj == null)
throw new NullPointerException();
else
super.add(obj);
//etc for any other methods that add to the list
}Then the list would never contain null, and you wouldn't have to worry about it, you'd only have to check for nulls when adding items, and if you use auto-boxing you wouldn't have to even then. -
Implementing an ArrayList as a Primitive Array. Plzzz Help a Newbie!!!
Hi I am a newbie to Java,
I have the following question, could someone please demonstrate some code to answer it?...
Q)
The Java class ArrayList uses a primitve array as its internal data structure and provides methods to access the array elements.
Write a implentation of a basic version of ArrayList providing methods to get, set, insert and delete elements. It should be possible to insert and delete at any position within the ArrayList. The methods should throw exceptions as necessary. Include one or more appropriate constructors.
Thanks in advance
CarlHi I am a newbie to Java,
I have the following question, could someone please
demonstrate some code to answer it?...
Q)
The Java class ArrayList uses a primitve array as its
internal data structure and provides methods to
access the array elements.
Write a implentation of a basic version of ArrayList
providing methods to get, set, insert and delete
elements. It should be possible to insert and delete
at any position within the ArrayList. The methods
should throw exceptions as necessary. Include one or
more appropriate constructors.
Thanks in advance
CarlNo it doesn't. It uses an object array. The question itself demonstrates that the author was either sleepy or not very knowledgeable to begin with as they either consider an array of objects a "primitive array" or they think all arrays are primitives.
Regardless, what I suspect they want from you is more or less a Collection backed by an array. For an example of one look at ArrayList's source code to begin with. -
Sort an an arrayList by the first element of an array
Hi,
I am really struggling trying to sort an arratList of arrays. I have an arrayList
ArrayList<String[]> myArrayList = new ArrayList<String []>(100);
Within this array I have may arrays with 2 elements
String[] myArray1 = {"Peter", "London"};
String[] myArray2 = {"John", "London"};
String[] myArray3 = {"Tony", "Birmingham"};
I add all these arrays to the arrayList and want to sort by the first element of the array. Basically I expect the final arrayList to be in the order of:
"John", "London"
"Peter", "London"
"Tony", "London"
Thanks
PeterHi,
I am really struggling trying to sort an arratList of
arrays. I have an arrayList
ArrayList<String[]> myArrayList = new
ArrayList<String []>(100);
Within this array I have may arrays with 2 elements
String[] myArray1 = {"Peter", "London"};
String[] myArray2 = {"John", "London"};
String[] myArray3 = {"Tony", "Birmingham"};
I add all these arrays to the arrayList and want to
sort by the first element of the array. Basically I
expect the final arrayList to be in the order of:
"John", "London"
"Peter", "London"
"Tony", "London"
Thanks
PeterThis can be done by using
Collections.sort(myArrayList, new Comparator<String[]>() {
public int compare(String[] s1, String[] s2) {
if (s1.length() <1) {
return -1;
if (s2.length() <1) {
return 1;
return s1[0].compareTo(s2[0]);
}); -
Using a vector / array/ arraylist. . something! . . . to return an image
I'm trying to create a class with a method that randomly returns one of five images. I can't figure out how to do it. Everything I try goes wrong because I can't figure out what kind of object to create in the method. My latest attempt (below) was with ArrayList, but the compiler keeps telling me:
smallPix2.java:32: array required, but java.util.ArrayList found
return icons[num];
Here's the code. Any feedback appreciated:
import javax.swing.*;
import javax.swing.border.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
//import java.util.ArrayList;
//import java.util.Arrays;
//import java.util.Random;
public class smallPix2 extends JFrame {
ImageIcon img1 = new ImageIcon("Art//boutet.jpg");
ImageIcon img2 = new ImageIcon("Art//curlu.jpg");
ImageIcon img3 = new ImageIcon("Art//helleu.jpg");
ImageIcon img4 = new ImageIcon("Art//ranson.jpg");
ImageIcon img5 = new ImageIcon("Art//zamora.jpg");
ImageIcon picks() {
ArrayList icons = new ArrayList();
icons.add(img1);
icons.add(img2);
icons.add(img3);
icons.add(img4);
icons.add(img5);
Random rando = new Random();
int num = rando.nextInt(5);
return icons[num];
}you have defined icons to be an ArrayList. So to reterieve data from it you should use its get() method.
icons.get(num);if you look at the ArrayList API, this will return a type Object. You obviosly want to return an ImageIcon, and seeings you know that they are ImageIcons in there you can cast the object to ImageIcon:
return (ImageIcon)icons.get(num); -
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. -
Is it possible to persist and store arrays of primitive types using the Java Persistence API? If so, is there any special annotation that the array requires?
Don't use ASSOC Arrays. Use SETs.
Also increase the JTA timeout in Weblogic to like say 600 seconds. -
I've been trying to create an array of ArrayLists, and have been unsuccessful.
class program {
static ArrayList<String>[] var;
void method () {
var = new ArrayList<String>()[5];
}The error message I get is "array required, but java.util.ArrayList<java.lang.String> found"
Am I doing something wrong, or is there a better way to accomplish what I'm trying to?import java.util.ArrayList;
import java.util.List;
class W
public static void main(String[] args)
List<String> list1 = new ArrayList<String>();
list1.add("a");
list1.add("b");
List<String> list2 = new ArrayList<String>();
list2.add("c");
list2.add("d");
List[] anArray = {list1, list2};
System.out.println(anArray[0].get(1)); // "b", from 1st array element, 2nd list1 element
}
Maybe you are looking for
-
Having difficulty using iPod mini to move music to new computer
I followed the article titled "How to use your iPod to move your music to a new computer" and I am really stuck. I deleted all the music from my iPod (it's all still on iTunes on my old computer" but the music will not transfer to my iPod so that I c
-
OS X disk has no more space for available application memory. How do I erase to make space?
I can not get the pop up force quit to stop coming up.
-
Hi I am using OBIEE11g installation in linux box.When we install configuration tool "Creating ASinstance" failed.Could you please provide me any solution My NAT IP=10.112.182.83 IP Addres= 10.112.184.83 I added etc/host entry like(login root enter be
-
Data loading....reporting requiment
Hi ,Experts ... we have critical requirement here.. we have two data that is Actual data and SP(spring plan-sales forecast) Data with us.. The requirement for the particular report will look like this. 1)For Actuals , May'09 - Aug'09 data to be loade
-
Attribute 'content' is always requires
Hi for all, I have a view that returns some information. I tried removing the attribute 'Content' from view, but the SES requires that this column on the result. I wish that my return had a specific attribute, such as: fruits and vegetables. Today th