Arrays.equals() – check two arrays for equality

Arrays.equals() is a static method in Java’s java.util.Arrays class that is used to check if two arrays are equal. It provides a convenient way to compare arrays element-by-element for equality. The method is overloaded to handle arrays of different types, including primitive types (e.g., int, char, double) and object types.

Key Points of Arrays.equals()

1. Element-wise Comparison:
   • The method compares each corresponding pair of elements in the two arrays for equality.
   • For arrays of primitive types, it uses the == operator.
   • For arrays of object types, it uses the equals() method of the objects.
2. Array Length:
   • The two arrays must have the same length to be considered equal. If their lengths differ, Arrays.equals() returns false.
3. Handling Nulls:
   • If both arrays are null, Arrays.equals() returns true.
   • If one array is null and the other is not, it returns false.

Overloaded Methods

Here are the main overloaded variants of the Arrays.equals() method:

• public static boolean equals(boolean[] a, boolean[] a2)
• public static boolean equals(byte[] a, byte[] a2)
• public static boolean equals(char[] a, char[] a2)
• public static boolean equals(double[] a, double[] a2)
• public static boolean equals(float[] a, float[] a2)
• public static boolean equals(int[] a, int[] a2)
• public static boolean equals(long[] a, long[] a2)
• public static boolean equals(Object[] a, Object[] a2)
• public static boolean equals(short[] a, short[] a2)

Examples

Comparing Primitive Type Arrays

import java.util.Arrays;

public class ArrayEqualsExample {
    public static void main(String[] args) {
        int[] array1 = {1, 2, 3, 4, 5};
        int[] array2 = {1, 2, 3, 4, 5};
        int[] array3 = {5, 4, 3, 2, 1};

        // Compare array1 and array2
        boolean isEqual = Arrays.equals(array1, array2);
        System.out.println("array1 and array2 are equal: " + isEqual); // Output: true

        // Compare array1 and array3
        isEqual = Arrays.equals(array1, array3);
        System.out.println("array1 and array3 are equal: " + isEqual); // Output: false
    }
}

Comparing Object Type Arrays

import java.util.Arrays;

public class ArrayEqualsExample {
    public static void main(String[] args) {
        String[] array1 = {"apple", "banana", "cherry"};
        String[] array2 = {"apple", "banana", "cherry"};
        String[] array3 = {"apple", "banana", "date"};

        // Compare array1 and array2
        boolean isEqual = Arrays.equals(array1, array2);
        System.out.println("array1 and array2 are equal: " + isEqual); // Output: true

        // Compare array1 and array3
        isEqual = Arrays.equals(array1, array3);
        System.out.println("array1 and array3 are equal: " + isEqual); // Output: false
    }
}

Important Considerations

• Performance: Arrays.equals() performs a linear search and compares each element. Its time complexity is O(n) where n is the number of elements in the array.
• Multidimensional Arrays: For multidimensional arrays, Arrays.equals() does not compare nested arrays element-wise. Instead, you should use Arrays.deepEquals() for deep comparison of nested arrays.

Comparing Multidimensional Arrays

import java.util.Arrays;

public class ArrayDeepEqualsExample {
    public static void main(String[] args) {
        int[][] array1 = {{1, 2, 3}, {4, 5, 6}};
        int[][] array2 = {{1, 2, 3}, {4, 5, 6}};
        int[][] array3 = {{1, 2, 3}, {6, 5, 4}};

        // Compare array1 and array2
        boolean isEqual = Arrays.deepEquals(array1, array2);
        System.out.println("array1 and array2 are equal: " + isEqual); // Output: true

        // Compare array1 and array3
        isEqual = Arrays.deepEquals(array1, array3);
        System.out.println("array1 and array3 are equal: " + isEqual); // Output: false
    }
}

In summary, Arrays.equals() is a useful method for comparing arrays element-by-element, and it’s essential to use the appropriate variant or method (like Arrays.deepEquals()) for your specific use case.