CODEWITHSUNDEEP
javaarrayslisttostring
Query9000
Query9000

Reputation: 11

java displaying List element as string

I am following a Stream tutorial but I do not understand what I need to do to have the List elements output the content as the numbers contained within.

Given two lists of numbers, how would you return all pairs of numbers? For example, given a list [1, 2, 3] and a list [3, 4] you should return [(1, 3), (1, 4), (2, 3), (2, 4), (3, 3), (3, 4)]. For simplicity, you can represent a pair as an array with two elements.

I have read a few posts about overriding toString() but I have no object to override. I am clearly missing something about the nature of 'pairs', is it because 'pairs' is a List of int[][]?

package testcode;
import java.util.Arrays;
import java.util.List;
import static java.util.stream.Collectors.toList;

public class TestCode {

public TestCode(){
    testStream();
}

public static void main(String[] args) {
    TestCode tC = new TestCode();
}

public void testStream(){
    List<Integer> numbers1 = Arrays.asList(1,2,3);
    List<Integer> numbers2 = Arrays.asList(3,4);
    List<int[]> pairs = numbers1.stream()
            .flatMap(i -> numbers2.stream()
                    .map(j -> new int[]{i, j})
            )
            .collect(toList());
    pairs.forEach(System.out::println);
//I have also tried 
    //String a = Arrays.toString(pairs); // but no suitable method found.
    String list = pairs.toString();
    System.out.println("list = " + list);
//tried converting pairs element to a List<String> using concatenation to force it be a string.
    List<String> stringsList  = new ArrayList<String>(pairs.size()); 
    for (int i = 0 ; i < pairs.size() ; i++) {
        stringsList.add("" + pairs.get(i));   
    }
    stringsList.forEach(System.out::println);
// or   
    System.out.println(" ** test 2");
    String[] stringsList2  = new String[pairs.size()]; 
    for (int i = 0 ; i < pairs.size() ; i++) {
        stringsList2[i] = "" + pairs.get(i);
        System.out.println(stringsList2[i]);
    }
}

Cheers for reading.

Upvotes: 0

Views: 842

Answers (2)

Malik Brahimi
Malik Brahimi

Reputation: 16711

Just use a nested for loop to cycle through the arrays and concatenate casted strings.

public static String test_method() {
    int[] array1 = {1, 2, 3};
    int[] array2 = {3, 4};

    String string = "";

    for (int i: array1) {
        for (int j: array2) {
            String sub = "(" + String.valueOf(i) + ", " 
                             + String.valueOf(j) + ") ";
            string += sub;
        }
    }

    return string;
}

Upvotes: 1

ankh-morpork
ankh-morpork

Reputation: 1832

Arrays.deepToString(Object[] a) should accomplish what you need.

deepToString will recursively print the elements of a multidimensional array.

Example

Code

import java.util.Arrays;
public class Test{
    public static void main(String[] args){
        int[][] test = {{1,2,3},{4,5,6},{7,8,9}};
        System.out.println(Arrays.deepToString(test));
    }
}

Output

[[1, 2, 3], [4, 5, 6], [7, 8, 9]]

Upvotes: 1

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