I have an arraylist, say arr. Now this arraylist stores numbers as strings. now i want to convert this arraylist to integer type. So how can i do that???
ArrayList arr = new ArrayList();
String a="Mode set - In Service", b="Mode set - Out of Service";
if(line.contains(a) || line.contains(b)) {
StringTokenizer st = new StringTokenizer(line, ":Mode set - Out of Service In Service");
while(st.hasMoreTokens()) {
arr.add(st.nextToken());
}
}
Since you're using an untyped List arr, you'll need to cast to String before performing parseInt:
List<Integer> arrayOfInts = new ArrayList<Integer>();
for (Object str : arr) {
arrayOfInts.add(Integer.parseInt((String)str));
}
I recommend that you define arr as follows:
List<String> arr = new ArrayList<String>();
That makes the cast in the conversion unnecessary.
run the below code,i hope it meets you requirement.
import java.util.*;
import java.lang.*;
import java.io.*;
class Ideone
{
public static void main (String[] args) throws java.lang.Exception
{
ArrayList<String> strArrayList= new ArrayList<String>();
strArrayList.add("1");
strArrayList.add("11");
strArrayList.add("111");
strArrayList.add("12343");
strArrayList.add("18475");
int[] ArrayRes = new int[strArrayList.size()];
int i = 0;
int x = 0;
for (String s : strArrayList)
{
ArrayRes[i] = Integer.parseInt(s);
System.out.println(ArrayRes[i]);
i++;
}
}
}
Output:
1
11
111
12343
18475
To convert to an integer array, you will input as a string array then go through each one and change it to an int.
public int[] convertStringArraytoIntArray(String[] sarray) throws Exception {
if (sarray != null) {
//new int for each string
int intarray[] = new int[sarray.length];
//for each int blah blah to array length i
for (int i = 0; i < sarray.length; i++) {
intarray[i] = Integer.parseInt(sarray[i]);
}
return intarray;
}
return null;
}
final List<String> strs = new ArrayList();
strs.add("1");
strs.add("2");
Integer[] ints = new Integer[strs.size()];
for (int i = 0; i<strs.size(); i++){
ints[i] = Integer.parseInt(strs.get(i));
}
use the Integer.parseInt() method.
http://www.java2s.com/Code/Java/Language-Basics/Convertstringtoint.htm
If you know that you have an arraylist of string but in your you wil use the same list as list of integer so better while initializing array list specify that the array list must insert only int type of data
instead of writing ArrayList arr = new ArrayList();
you could have written ArrayList<Integer> arr = new ArrayList<Integer>();
Alternate solution
If you want to convert that list into Integer ArrayList then use following code
How to convert String ArrayList into ArrayList of int
ArrayList<String> oldList = new ArrayList<String>();
oldList.add(""+5);
oldList.add(""+5);
ArrayList<Integer> newList = new ArrayList<Integer>(oldList.size());
for (String myInt : oldList) {
newList.add(Integer.parseInt(myInt));
}
Related
How might I convert an ArrayList<String> object to a String[] array in Java?
List<String> list = ..;
String[] array = list.toArray(new String[0]);
For example:
List<String> list = new ArrayList<String>();
//add some stuff
list.add("android");
list.add("apple");
String[] stringArray = list.toArray(new String[0]);
The toArray() method without passing any argument returns Object[]. So you have to pass an array as an argument, which will be filled with the data from the list, and returned. You can pass an empty array as well, but you can also pass an array with the desired size.
Important update: Originally the code above used new String[list.size()]. However, this blogpost reveals that due to JVM optimizations, using new String[0] is better now.
An alternative in Java 8:
String[] strings = list.stream().toArray(String[]::new);
Java 11+:
String[] strings = list.toArray(String[]::new);
Starting from Java-11, one can use the API Collection.toArray(IntFunction<T[]> generator) to achieve the same as:
List<String> list = List.of("x","y","z");
String[] arrayBeforeJDK11 = list.toArray(new String[0]);
String[] arrayAfterJDK11 = list.toArray(String[]::new); // similar to Stream.toArray
You can use the toArray() method for List:
ArrayList<String> list = new ArrayList<String>();
list.add("apple");
list.add("banana");
String[] array = list.toArray(new String[list.size()]);
Or you can manually add the elements to an array:
ArrayList<String> list = new ArrayList<String>();
list.add("apple");
list.add("banana");
String[] array = new String[list.size()];
for (int i = 0; i < list.size(); i++) {
array[i] = list.get(i);
}
Hope this helps!
ArrayList<String> arrayList = new ArrayList<String>();
Object[] objectList = arrayList.toArray();
String[] stringArray = Arrays.copyOf(objectList,objectList.length,String[].class);
Using copyOf, ArrayList to arrays might be done also.
In Java 8:
String[] strings = list.parallelStream().toArray(String[]::new);
In Java 8, it can be done using
String[] arrayFromList = fromlist.stream().toArray(String[]::new);
If your application is already using Apache Commons lib, you can slightly modify the accepted answer to not create a new empty array each time:
List<String> list = ..;
String[] array = list.toArray(ArrayUtils.EMPTY_STRING_ARRAY);
// or if using static import
String[] array = list.toArray(EMPTY_STRING_ARRAY);
There are a few more preallocated empty arrays of different types in ArrayUtils.
Also we can trick JVM to create en empty array for us this way:
String[] array = list.toArray(ArrayUtils.toArray());
// or if using static import
String[] array = list.toArray(toArray());
But there's really no advantage this way, just a matter of taste, IMO.
You can use Iterator<String> to iterate the elements of the ArrayList<String>:
ArrayList<String> list = new ArrayList<>();
String[] array = new String[list.size()];
int i = 0;
for (Iterator<String> iterator = list.iterator(); iterator.hasNext(); i++) {
array[i] = iterator.next();
}
Now you can retrive elements from String[] using any Loop.
Generics solution to covert any List<Type> to String []:
public static <T> String[] listToArray(List<T> list) {
String [] array = new String[list.size()];
for (int i = 0; i < array.length; i++)
array[i] = list.get(i).toString();
return array;
}
Note You must override toString() method.
class Car {
private String name;
public Car(String name) {
this.name = name;
}
public String toString() {
return name;
}
}
final List<Car> carList = new ArrayList<Car>();
carList.add(new Car("BMW"))
carList.add(new Car("Mercedes"))
carList.add(new Car("Skoda"))
final String[] carArray = listToArray(carList);
List<String> list = new ArrayList<>();
list.add("a");
list.add("b");
list.add("c");
String [] strArry= list.stream().toArray(size -> new String[size]);
Per comments, I have added a paragraph to explain how the conversion works.
First, List is converted to a String stream. Then it uses Stream.toArray to convert the elements in the stream to an Array. In the last statement above "size -> new String[size]" is actually an IntFunction function that allocates a String array with the size of the String stream. The statement is identical to
IntFunction<String []> allocateFunc = size -> {
return new String[size];
};
String [] strArry= list.stream().toArray(allocateFunc);
List <String> list = ...
String[] array = new String[list.size()];
int i=0;
for(String s: list){
array[i++] = s;
}
in case some extra manipulation of the data is desired, for which the user wants a function, this approach is not perfect (as it requires passing the class of the element as second parameter), but works:
import java.util.ArrayList;
import java.lang.reflect.Array;
public class Test {
public static void main(String[] args) {
ArrayList<Integer> al = new ArrayList<>();
al.add(1);
al.add(2);
Integer[] arr = convert(al, Integer.class);
for (int i=0; i<arr.length; i++)
System.out.println(arr[i]);
}
public static <T> T[] convert(ArrayList<T> al, Class clazz) {
return (T[]) al.toArray((T[])Array.newInstance(clazz, al.size()));
}
}
In Java 11, we can use the Collection.toArray(generator) method. The following code will create a new array of strings:
List<String> list = List.of("one", "two", "three");
String[] array = list.toArray(String[]::new)
from java.base's java.util.Collection.toArray().
You can convert List to String array by using this method:
Object[] stringlist=list.toArray();
The complete example:
ArrayList<String> list=new ArrayList<>();
list.add("Abc");
list.add("xyz");
Object[] stringlist=list.toArray();
for(int i = 0; i < stringlist.length ; i++)
{
Log.wtf("list data:",(String)stringlist[i]);
}
private String[] prepareDeliveryArray(List<DeliveryServiceModel> deliveryServices) {
String[] delivery = new String[deliveryServices.size()];
for (int i = 0; i < deliveryServices.size(); i++) {
delivery[i] = deliveryServices.get(i).getName();
}
return delivery;
}
An alternate one-liner method for primitive types, such as double, int, etc.:
List<Double> coordList = List.of(3.141, 2.71);
double[] doubleArray = coordList.mapToDouble(Double::doubleValue).toArray();
List<Integer> coordList = List.of(11, 99);
int[] intArray = coordList.mapToInt(Integer::intValue).toArray();
and so on...
Is there any possibility to merge two elements of ArrayList?
This is my array = [u,s,m,a,t,t]
and I want to have something like this = [us,matt]
I've tried to use toString(), and replace('',''), but it merges whole array [usmatt].
Any other options?
I don't know exactly what you mean but what you try to achieve could be done this way:
Pseudo-code:
String[] array1 = [u,s,m,a,t,t]
String a = array[0]+array[1]
String b = array[2]+array[3]+array[4]+array[5]
String[] array2 = [a,b]
Try this: (For any length ArrayList.)
public static void MergeArrayList() {
ArrayList<Character> Array = new ArrayList<Character>() {{ add('u');add('s');
add('m');add('a');add('t');add('t');}};
ArrayList<String> newArray = new ArrayList<>();
int n=2; // Change this to indicate where you need to make the cut.
String str="";
for (int i=0;i<Array.size();i++) {
if (i==n) {
newArray.add(str);
str="";
}
str += Array.get(i);
}
newArray.add(str);
System.out.println(Array);
System.out.println(newArray);
}
I want to store some data in an ArrayList<ArrayList<String>> variable into a csv file.
For this purpose, I zeroed in on Ostermiller Utilities- which include a CSV Writer as well.
The problem is, the csvwrite functionality requires a String, String[] or a String[][] variable.
I wont know beforehand the number of rows/columns in my ArrayList of arraylists-- so how do I use the above (cswrite) functionality? Dont I have to declare a fixed size for a String[]][] variable?
A String[][] is nothing more than an array of arrays. For example, this makes a 'triangular matrix' using a 2d array. It doesn't have to be a square (although CSV probably should be square, it doesn't have to be).
String[][] matrix = new String[][5];
matrix[0] = new String[1];
matrix[1] = new String[2];
matrix[2] = new String[3];
matrix[3] = new String[4];
matrix[4] = new String[5];
So for your purposes
String[][] toMatrix(ArrayList<ArrayList<String>> listOFLists) {
String[][] matrix = new String[][listOfLists.size()];
for(int i = 0; i < matrix.length; i++) {
matrix[i]= listOfLists.get(i).toArray();
}
return matrix;
}
Just keep in mind that in this case, it's in matrix[col][row], not matrix[row][col]. You may need to transpose this result, depending on the needs of your library.
Tested and working:
String[][] arrayOfArraysOfString = new String[arrayListOfArrayListsOfStrings.size()][];
for (int index = 0; index < arrayListOfArrayListsOfStrings.size(); index++) {
ArrayList<String> arrayListOfString = arrayListOfArrayListsOfStrings.get(index);
if (arrayListOfString != null) {
arrayOfArraysOfString[index] = arrayListOfString.toArray(new String[arrayListOfString.size()]);
}
}
Here is an Example of how to convert your multidimesional ArrayList into a multidimensional String Array.
package stuff;
import java.util.ArrayList;
public class ArrayTest {
public static void main(String[] args) throws Exception {
ArrayList<ArrayList<String>> multidimesionalArrayList = createArrayListContent();
String[][] multidimensionalStringArray = new String[multidimesionalArrayList.size()][];
int index = 0;
for (ArrayList<String> strings : multidimesionalArrayList) {
multidimensionalStringArray[index] = strings.toArray(new String[]{});
index++;
}
System.out.println(multidimensionalStringArray);
}
private static ArrayList<ArrayList<String>> createArrayListContent() throws Exception {
ArrayList<ArrayList<String>> result = new ArrayList<ArrayList<String>>();
result.add(createArrayList());
result.add(createArrayList());
result.add(createArrayList());
result.add(createArrayList());
result.add(createArrayList());
return result;
}
private static ArrayList<String> createArrayList() throws Exception {
ArrayList<String> list = new ArrayList<String>();
list.add(String.valueOf(System.currentTimeMillis()));
Thread.sleep(10);
list.add(String.valueOf(System.currentTimeMillis()));
Thread.sleep(10);
list.add(String.valueOf(System.currentTimeMillis()));
Thread.sleep(10);
list.add(String.valueOf(System.currentTimeMillis()));
Thread.sleep(10);
list.add(String.valueOf(System.currentTimeMillis()));
return list;
}
}
You can create an array of arrays (matrix) with one size at first, and then iterate and add the data as you traverse the list of list
String[][] arr = new String[listOfList.size()][];
int i = 0;
for (List<String> row: listOfList) {
arr[i++] = row.toArray(new String[row.size()]);
}
I have an ArrayList with values like "abcd#xyz" and "mnop#qrs". I want to convert it into an Array and then split it with # as delimiter and have abcd,mnop in an array and xyz,qrs in another array. I tried the following code:
String dsf[] = new String[al.size()];
for(int i =0;i<al.size();i++){
dsf[i] = al.get(i);
}
But it failed saying "Ljava.lang.String;#57ba57ba"
You don't need to reinvent the wheel, here's the toArray() method:
String []dsf = new String[al.size()];
al.toArray(dsf);
List<String> list=new ArrayList<String>();
list.add("sravan");
list.add("vasu");
list.add("raki");
String names[]=list.toArray(new String[list.size()])
List<String> list=new ArrayList<String>();
list.add("sravan");
list.add("vasu");
list.add("raki");
String names[]=list.toArray(new String[0]);
if you see the last line (new String[0]), you don't have to give the size, there are time when we don't know the length of the list, so to start with giving it as 0 , the constructed array will resize.
import java.util.*;
public class arrayList {
public static void main(String[] args) {
Scanner sc=new Scanner(System.in);
ArrayList<String > x=new ArrayList<>();
//inserting element
x.add(sc.next());
x.add(sc.next());
x.add(sc.next());
x.add(sc.next());
x.add(sc.next());
//to show element
System.out.println(x);
//converting arraylist to stringarray
String[]a=x.toArray(new String[x.size()]);
for(String s:a)
System.out.print(s+" ");
}
}
String[] values = new String[arrayList.size()];
for (int i = 0; i < arrayList.size(); i++) {
values[i] = arrayList.get(i).type;
}
What you did with the iteration is not wrong from what I can make of it based on the question. It gives you a valid array of String objects. Like mentioned in another answer it is however easier to use the toArray() method available for the ArrayList object => http://docs.oracle.com/javase/1.5.0/docs/api/java/util/ArrayList.html#toArray%28%29
Just a side note. If you would iterate your dsf array properly and print each element on its own you would get valid output. Like this:
for(String str : dsf){
System.out.println(str);
}
What you probably tried to do was print the complete Array object at once since that would give an object memory address like you got in your question. If you see that kind of output you need to provide a toString() method for the object you're printing.
package com.v4common.shared.beans.audittrail;
import java.util.ArrayList;
import java.util.List;
public class test1 {
public static void main(String arg[]){
List<String> list = new ArrayList<String>();
list.add("abcd#xyz");
list.add("mnop#qrs");
Object[] s = list.toArray();
String[] s1= new String[list.size()];
String[] s2= new String[list.size()];
for(int i=0;i<s.length;i++){
if(s[i] instanceof String){
String temp = (String)s[i];
if(temp.contains("#")){
String[] tempString = temp.split("#");
for(int j=0;j<tempString.length;j++) {
s1[i] = tempString[0];
s2[i] = tempString[1];
}
}
}
}
System.out.println(s1.length);
System.out.println(s2.length);
System.out.println(s1[0]);
System.out.println(s1[1]);
}
}
Here is the solution for you given scenario -
List<String>ls = new ArrayList<String>();
ls.add("dfsa#FSDfsd");
ls.add("dfsdaor#ooiui");
String[] firstArray = new String[ls.size()];
firstArray =ls.toArray(firstArray);
String[] secondArray = new String[ls.size()];
for(int i=0;i<ls.size();i++){
secondArray[i]=firstArray[i].split("#")[0];
firstArray[i]=firstArray[i].split("#")[1];
}
This is the right answer you want and this solution i have run my self on netbeans
ArrayList a=new ArrayList();
a.add(1);
a.add(3);
a.add(4);
a.add(5);
a.add(8);
a.add(12);
int b[]= new int [6];
Integer m[] = new Integer[a.size()];//***Very important conversion to array*****
m=(Integer[]) a.toArray(m);
for(int i=0;i<a.size();i++)
{
b[i]=m[i];
System.out.println(b[i]);
}
System.out.println(a.size());
This can be done using stream:
List<String> stringList = Arrays.asList("abc#bcd", "mno#pqr");
List<String[]> objects = stringList.stream()
.map(s -> s.split("#"))
.collect(Collectors.toList());
The return value would be arrays of split string.
This avoids converting the arraylist to an array and performing the operation.
NameOfArray.toArray(new String[0])
This will convert ArrayList to Array in java
// A Java program to convert an ArrayList to arr[]
import java.io.*;
import java.util.List;
import java.util.ArrayList;
class Main {
public static void main(String[] args)
{
List<Integer> al = new ArrayList<Integer>();
al.add(10);
al.add(20);
al.add(30);
al.add(40);
Integer[] arr = new Integer[al.size()];
arr = al.toArray(arr);
for (Integer x : arr)
System.out.print(x + " ");
}
}
How might I convert an ArrayList<String> object to a String[] array in Java?
List<String> list = ..;
String[] array = list.toArray(new String[0]);
For example:
List<String> list = new ArrayList<String>();
//add some stuff
list.add("android");
list.add("apple");
String[] stringArray = list.toArray(new String[0]);
The toArray() method without passing any argument returns Object[]. So you have to pass an array as an argument, which will be filled with the data from the list, and returned. You can pass an empty array as well, but you can also pass an array with the desired size.
Important update: Originally the code above used new String[list.size()]. However, this blogpost reveals that due to JVM optimizations, using new String[0] is better now.
An alternative in Java 8:
String[] strings = list.stream().toArray(String[]::new);
Java 11+:
String[] strings = list.toArray(String[]::new);
Starting from Java-11, one can use the API Collection.toArray(IntFunction<T[]> generator) to achieve the same as:
List<String> list = List.of("x","y","z");
String[] arrayBeforeJDK11 = list.toArray(new String[0]);
String[] arrayAfterJDK11 = list.toArray(String[]::new); // similar to Stream.toArray
You can use the toArray() method for List:
ArrayList<String> list = new ArrayList<String>();
list.add("apple");
list.add("banana");
String[] array = list.toArray(new String[list.size()]);
Or you can manually add the elements to an array:
ArrayList<String> list = new ArrayList<String>();
list.add("apple");
list.add("banana");
String[] array = new String[list.size()];
for (int i = 0; i < list.size(); i++) {
array[i] = list.get(i);
}
Hope this helps!
ArrayList<String> arrayList = new ArrayList<String>();
Object[] objectList = arrayList.toArray();
String[] stringArray = Arrays.copyOf(objectList,objectList.length,String[].class);
Using copyOf, ArrayList to arrays might be done also.
In Java 8:
String[] strings = list.parallelStream().toArray(String[]::new);
In Java 8, it can be done using
String[] arrayFromList = fromlist.stream().toArray(String[]::new);
If your application is already using Apache Commons lib, you can slightly modify the accepted answer to not create a new empty array each time:
List<String> list = ..;
String[] array = list.toArray(ArrayUtils.EMPTY_STRING_ARRAY);
// or if using static import
String[] array = list.toArray(EMPTY_STRING_ARRAY);
There are a few more preallocated empty arrays of different types in ArrayUtils.
Also we can trick JVM to create en empty array for us this way:
String[] array = list.toArray(ArrayUtils.toArray());
// or if using static import
String[] array = list.toArray(toArray());
But there's really no advantage this way, just a matter of taste, IMO.
You can use Iterator<String> to iterate the elements of the ArrayList<String>:
ArrayList<String> list = new ArrayList<>();
String[] array = new String[list.size()];
int i = 0;
for (Iterator<String> iterator = list.iterator(); iterator.hasNext(); i++) {
array[i] = iterator.next();
}
Now you can retrive elements from String[] using any Loop.
Generics solution to covert any List<Type> to String []:
public static <T> String[] listToArray(List<T> list) {
String [] array = new String[list.size()];
for (int i = 0; i < array.length; i++)
array[i] = list.get(i).toString();
return array;
}
Note You must override toString() method.
class Car {
private String name;
public Car(String name) {
this.name = name;
}
public String toString() {
return name;
}
}
final List<Car> carList = new ArrayList<Car>();
carList.add(new Car("BMW"))
carList.add(new Car("Mercedes"))
carList.add(new Car("Skoda"))
final String[] carArray = listToArray(carList);
List<String> list = new ArrayList<>();
list.add("a");
list.add("b");
list.add("c");
String [] strArry= list.stream().toArray(size -> new String[size]);
Per comments, I have added a paragraph to explain how the conversion works.
First, List is converted to a String stream. Then it uses Stream.toArray to convert the elements in the stream to an Array. In the last statement above "size -> new String[size]" is actually an IntFunction function that allocates a String array with the size of the String stream. The statement is identical to
IntFunction<String []> allocateFunc = size -> {
return new String[size];
};
String [] strArry= list.stream().toArray(allocateFunc);
List <String> list = ...
String[] array = new String[list.size()];
int i=0;
for(String s: list){
array[i++] = s;
}
in case some extra manipulation of the data is desired, for which the user wants a function, this approach is not perfect (as it requires passing the class of the element as second parameter), but works:
import java.util.ArrayList;
import java.lang.reflect.Array;
public class Test {
public static void main(String[] args) {
ArrayList<Integer> al = new ArrayList<>();
al.add(1);
al.add(2);
Integer[] arr = convert(al, Integer.class);
for (int i=0; i<arr.length; i++)
System.out.println(arr[i]);
}
public static <T> T[] convert(ArrayList<T> al, Class clazz) {
return (T[]) al.toArray((T[])Array.newInstance(clazz, al.size()));
}
}
In Java 11, we can use the Collection.toArray(generator) method. The following code will create a new array of strings:
List<String> list = List.of("one", "two", "three");
String[] array = list.toArray(String[]::new)
from java.base's java.util.Collection.toArray().
You can convert List to String array by using this method:
Object[] stringlist=list.toArray();
The complete example:
ArrayList<String> list=new ArrayList<>();
list.add("Abc");
list.add("xyz");
Object[] stringlist=list.toArray();
for(int i = 0; i < stringlist.length ; i++)
{
Log.wtf("list data:",(String)stringlist[i]);
}
private String[] prepareDeliveryArray(List<DeliveryServiceModel> deliveryServices) {
String[] delivery = new String[deliveryServices.size()];
for (int i = 0; i < deliveryServices.size(); i++) {
delivery[i] = deliveryServices.get(i).getName();
}
return delivery;
}
An alternate one-liner method for primitive types, such as double, int, etc.:
List<Double> coordList = List.of(3.141, 2.71);
double[] doubleArray = coordList.mapToDouble(Double::doubleValue).toArray();
List<Integer> coordList = List.of(11, 99);
int[] intArray = coordList.mapToInt(Integer::intValue).toArray();
and so on...