在Java中从int数组转换为Integer arraylist

Question

I have a problem in converting from Array to ArrayList

public class one 
{
public static void main(String args[])
{
int y[]={12,25,38,46};
two p=new two();
p.setLocations(y);
}
}


import java.io.*;
import java.util.*;   

public class two 
{
    ArrayList<Integer> data_array=new ArrayList<Integer>();


void setLocations(int locations[])
{
        ArrayList<Integer> locations_arraylist=new ArrayList(Arrays.asList(locations));
        data_array=locations_arraylist;
    for(int i=0;i<data_array.size();i++)
        System.out.println("data_array["+i+"]="+data_array.get(i));
}
}

In the below line

ArrayList<Integer> locations_arraylist=new  ArrayList(Arrays.asList(locations));
//Copying from array to ArrayList-Its converting,Please suggest

Answer 1

An int[] is quite different from a List<Integer> . For example, an Integer has an identity as well as a value. There is no very simple way to do the conversion.

The following way works with Java 8.

int[] array = {1, 2, 3, 4, 5};
List<Integer> list = IntStream.of(array).boxed().collect(Collectors.toCollection(ArrayList::new));

The following way works in earlier versions.

int[] array = {1, 2, 3, 4, 5};
List<Integer> list = new ArrayList<Integer>();
for (int a : array)
    list.add(a);

If you pass an int[] to Arrays.asList you get a List<int[]> , not a List<Integer> .

Answer 2

It is recommended to use the interface List for members/variables and use the ArrayList constructor. Also ArrayList without the brackets indicates the raw type instead of instead of the generic.

If you would like to avoid a for loop that will copy the values from array to List , there are 2 solutions :

1. Guava (put on top import com.google.common.primitives.Ints; )

    List<Integer> locations_arraylist = Ints.asList(locations); 

2. pass the values to Arrays.asList() directly

    List<Integer> locations_arraylist = Arrays.asList(12, 25, 38, 46); 

Answer 3

You can try this:

replace int y[]={12,25,38,46}; to Integer y[] = {12, 25, 38, 46};
No need of this line as well
ArrayList<Integer> data_array = new ArrayList<Integer>();
You can use for-each loop for print the array :

int i=0;
        for (Integer locations_arraylist1 : locations_arraylist) {
             System.out.println("data_array[" + i + "]=" + locations_arraylist1);
             i++;
        }

Answer 4

Try this:

int[] arrayInt = new int[]{1, 2, 3};
List<Integer> list = Arrays.asList(ArrayUtils.toObject(arrayInt));