Sorting and comparing integer arrays in Java

Question

I am able to sort arrays, and able to compare arrays in separate steps, but when I attempt to do both in the same line, I get an error. From the Java documentation, the sort method should return an array of the same type passed into it, and the equals method should return a boolean value.

What am I misunderstanding/misusing here?

Here is my code for testing the situation:

import java.util.Arrays;

public class test {

    public static void main(String[] args) {
        int[] arr1 = {2,4,5,3,1};
        int[] arr2 = {4,3,2,1,5};

        if (Arrays.equals(Arrays.sort(arr1), Arrays.sort(arr2))) {  // Problem line
        System.out.println("Same contents");
        }
        else {
        System.out.println("Different contents");
        }
    }
}

As far as I can see, I have created 2 arrays with the same contents. I then call Arrays.equals(), and for its 2 arguments, I pass in the results of calling Arrays.sort() on each array.

When trying to compile, I get the following error:

test.java:9: error: 'void' type not allowed here
        if (Arrays.equals(Arrays.sort(arr1), Arrays.sort(arr2))) {
                                     ^
test.java:9: error: 'void' type not allowed here
        if (Arrays.equals(Arrays.sort(arr1), Arrays.sort(arr2))) {
                                                        ^
2 errors
shell returned 1

What is the documented return type of Arrays.sort(). The javadoc is your friend. Read it. — JB Nizet
– JB Nizet, Commented Mar 7, 2016 at 21:23
@JBNizet Yep, that'll do it. I did have a read through it, but obviously confused my self into thinking an array was returned. Thank you. — Shinkawa91
– Shinkawa91, Commented Mar 7, 2016 at 21:30

jdabrowski · Accepted Answer · 2016-03-07 21:22:59Z

3

Arrays.sort() method does not return the array;

Do this:

Arrays.sort(arr1);
Arrays.sort(arr2);
if (Arrays.equals(arr1, arr2)) {
// rest of code

answered Mar 7, 2016 at 21:22

jdabrowski

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kosa · Accepted Answer · 2016-03-07 21:22:55Z

2

Arrays.sort returns void type. You need valid array type to use Arrays.equals(int[] a, int[] a2)

answered Mar 7, 2016 at 21:22

kosa

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