Comparing Arrays in Java

Comparing two integer arrays in Java

public static void compareArrays(int[] array1, int[] array2) {
        boolean b = true;
        if (array1 != null && array2 != null){
          if (array1.length != array2.length)
              b = false;
          else
              for (int i = 0; i < array2.length; i++) {
                  if (array2[i] != array1[i]) {
                      b = false;    
                  }                 
            }
        }else{
          b = false;
        }
        System.out.println(b);
    }

How to compare int arrays in Java?

A few things to note here:

== compares the references, not the values . . . that is, you are asking whether these two arrays are the same exact instance, not whether they contain the same values.
The fact that you are using == means you may not know about the equals() method on Object. This is not the method you'll need to solve this current problem, but just be aware that in general, when you compare the values of two objects, you should be using obj1.equals(obj2), not obj1 == obj2. Now == does work with primitives like int (e.g. plain old x == 3 and so on), so maybe that's why you were using it, but I just wanted to make sure you were aware of equals() vs. ==.
In the old old days (pre-1998), you would have to compare each element pair of the two arrays. Nowadays, you can just use that static Arrays.equals() method on the java.util.Arrays class. This method is overloaded for all the primitive types (using == under the hood for each element pair) and for Object (where it will most definitely use equals() for each pair.)

Compare two array and return an array to show which elements are equal or not

In the second loop when comparing both matrices if they are equal you must set the flag to true and break the second loop, so the first loop will compare the next element, for example:

int[] arr1 = {1, 2, 3, 4, 5};
int[] arr2 = {1, 3};

HashMap<Integer, Boolean> map = new HashMap<>();

for (int i : arr1) {
    for (int j : arr2) {
        if (j == i) {
            map.put(i, true);
            break;
        } else {
            map.put(i, false);
        }
    }
}

System.out.println(Arrays.asList(map));

Output:

[{1=true, 2=false, 3=true, 4=false, 5=false}]

How to compare two-dimensional (or nested) Java Arrays?

You are comparing two dimensional arrays, which means the elements of these arrays are themselves arrays. Therefore, when the elements are compared (using Object's equals), false is returned, since Object's equals compares Object references.

Use Arrays.deepEquals instead.

From the Javadoc:

boolean java.util.Arrays.deepEquals(Object[] a1, Object[] a2)

Returns true if the two specified arrays are deeply equal to one another. Unlike the equals(Object [], Object []) method, this method is appropriate for use with nested arrays of arbitrary depth.

Java Comparing Two Arrays for Login

You might want to use a map for this.

the map will return null if the user doesn't exist so the check will fail.
or it will return the password for the user and the password check will fail.
Returns are immediate after the result message is displayed.


static Map<String, String> users = new HashMap<>();
    
String[] username = { "admin", "john", "alina" };
String[] password = { "123", "456", "789" };
// build the map.
for (int i = 0; i < username.length; i++) {
    users.put(username[i], password[i]);
}
userLogin();

    
public static boolean userLogin() { 
    Scanner input = new Scanner(System.in);
    System.out.println("Enter your username: ");
    String user = input.nextLine();
    
    System.out.println("Enter your password: ");
    String pass = input.nextLine();
    
    String password = users.get(user);
    if (pass.equals(password)) {
        System.out.println("Login Success! Loading the menu...");
        return true;
    }
    System.out.println(
            "Invalid username or password, please contact your Database Administrator for "
                    + "support!");
    
    return false;
}

comparing arrays in java

Use Arrays.equals method. Example:

boolean b = Arrays.equals(nir1, nir2); //prints true in this case

How to compare arrays without using .equals and with a false boolean

Instead of immediately returning when they are equal, check for inequalities and if there's one, then return false. If the for loop finishes without returning, then you can safely return true.

if (arrayOne.length == arrayTwo.length) {

    for (int i = 0; i < arrayOne.length; i ++) {

        if (arrayOne [ i ] != arrayTwo [ i ] ) {

            return false; 
        }

    }

    return true;

}
return false;

Comparing elements of arrays in java

So you want to //Do Something if the ParkedCar's 5th value is higher than the minutes purchased.

You can write a function to do this.
Including checks for if both arrays are same size.
Your function is simply

   for(int i = 0, i < parkingLot.getLength(), i++) {
        if(parkingLot[i].getFifthValue() > meters[i].getMinutesPurchased()))
               //DoSomething
   }

However, ParkedMeter is quite a simple class. Why not add that as an attribute to ParkedCar. In that case, this meter value check is simply a oneliner boolean function in your ParkedCar Class return fifthValue > minutesPurchased;

Comparing two arrays of String and returning comparison in Java

using the stream API, you could do:

String[] result = Arrays.stream(a1)
                        .filter(new HashSet<>(Arrays.asList(a2))::contains)
                        .toArray(String[]::new);

Edit:

just for those curious about whether a new set will be constructed for each element, this is not the case at all.

only one Set instance is constructed, the above code is equivalent to:

List<String> list = new ArrayList<>();
HashSet<String> strings = new HashSet<>(Arrays.asList(a2));
for (String s : a1) { 
   if (strings.contains(s)) list.add(s); 
}
String[] result = list.toArray(new String[0]);