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Roger
Roger

Reputation: 1459

Compare two Byte Arrays? (Java)

I have a byte array with a ~known binary sequence in it. I need to confirm that the binary sequence is what it's supposed to be. I have tried .equals in addition to ==, but neither worked. 

byte[] array = new BigInteger("1111000011110001", 2).toByteArray();
if (new BigInteger("1111000011110001", 2).toByteArray() == array){
    System.out.println("the same");
} else {
    System.out.println("different'");
}

Upvotes: 103

Views: 121656

Answers (6)

Sylhare
Sylhare

Reputation: 7119

Since I wanted to compare two arrays for a unit Test and I arrived on this answer I thought I could share.

You can also do it with:

@Test
public void testTwoArrays() {
  byte[] array = new BigInteger("1111000011110001", 2).toByteArray();
  byte[] secondArray = new BigInteger("1111000011110001", 2).toByteArray();

  Assert.assertArrayEquals(array, secondArray);
}

And you could check on Comparing arrays in JUnit assertions for more infos.

Upvotes: 2

PixelsTech
PixelsTech

Reputation: 3346

You can use both Arrays.equals() and MessageDigest.isEqual(). These two methods have some differences though.

MessageDigest.isEqual() is a time-constant comparison method and Arrays.equals() is non time-constant and it may bring some security issues if you use it in a security application.

The details for the difference can be read at Arrays.equals() vs MessageDigest.isEqual()

Upvotes: 11

Bamaco
Bamaco

Reputation: 590

Of course, the accepted answer of Arrays.equal( byte[] first, byte[] second ) is correct. I like to work at a lower level, but I was unable to find a low level efficient function to perform equality test ranges. I had to whip up my own, if anyone needs it:

public static boolean ArraysAreEquals(
 byte[] first,
 int firstOffset,
 int firstLength,
 byte[] second,
 int secondOffset,
 int secondLength
) {
    if( firstLength != secondLength ) {
        return false;
    }

    for( int index = 0; index < firstLength; ++index ) {
        if( first[firstOffset+index] != second[secondOffset+index]) {
            return false;
        }
    }

    return true;
}

Upvotes: 4

Brian Roach
Brian Roach

Reputation: 76918

In your example, you have:

if (new BigInteger("1111000011110001", 2).toByteArray() == array)

When dealing with objects, == in java compares reference values. You're checking to see if the reference to the array returned by toByteArray() is the same as the reference held in array, which of course can never be true. In addition, array classes don't override .equals() so the behavior is that of Object.equals() which also only compares the reference values.

To compare the contents of two arrays, static array comparison methods are provided by the Arrays class

byte[] array = new BigInteger("1111000011110001", 2).toByteArray();
byte[] secondArray = new BigInteger("1111000011110001", 2).toByteArray();
if (Arrays.equals(array, secondArray))
{
    System.out.println("Yup, they're the same!");
}

Upvotes: 175

jswolf19
jswolf19

Reputation: 2303

Java doesn't overload operators, so you'll usually need a method for non-basic types. Try the Arrays.equals() method.

Upvotes: 11

Ernest Friedman-Hill
Ernest Friedman-Hill

Reputation: 81734

Check out the static java.util.Arrays.equals() family of methods. There's one that does exactly what you want.

Upvotes: 64

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