Java: equals() vs Arrays.equals

array1.equals(array2) method return true, if both the array references point to same object (same as array1 == array2), else false.

Arrays.equals() method is available in below forms, it return true if both arrays contain the same number of elements, and all corresponding pairs of elements in the two arrays are equal.

public static boolean equals(byte[] a, byte[] a2)

public static boolean equals(short[] a, short[] a2)

public static boolean equals(int[] a, int[] a2)

public static boolean equals(long[] a, long[] a2)

public static boolean equals(float[] a, float[] a2)

public static boolean equals(double[] a, double[] a2)

public static boolean equals(char[] a, char[] a2)

public static boolean equals(boolean[] a, boolean[] a2)

public static boolean equals(Object[] a, Object[] a2)

App.java

package com.sample.app;

import java.util.Arrays;

public class App {

 public static void main(String args[]) {
  int[] data1 = { 2, 3, 5, 7 };
  int[] data2 = { 2, 3, 5, 7 };
  int[] data3 = data1;

  System.out.println("data1.equals(data2) : " + data1.equals(data2));
  System.out.println("data1.equals(data3) : " + data1.equals(data3));
  
  System.out.println("Arrays.equals(data1, data2) : " + Arrays.equals(data1, data2));
  System.out.println("Arrays.equals(data1, data3) : " + Arrays.equals(data1, data3));

 }

}

Output

data1.equals(data2) : false

data1.equals(data3) : true

Arrays.equals(data1, data2) : true

Arrays.equals(data1, data3) : true

Note

'Arrays.equals()'' do not work as expected for multidimensional arrays, it compares items of the 1st dimension for reference equality.

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Java: String equals vs compareTo

We can figure out the differences between equals and comapreTo methods, by looking at the source code.

public boolean equals(Object anObject) {
    if (this == anObject) {
        return true;
    }
    if (anObject instanceof String) {
        String anotherString = (String)anObject;
        int n = value.length;
        if (n == anotherString.value.length) {
            char v1[] = value;
            char v2[] = anotherString.value;
            int i = 0;
            while (n-- != 0) {
                if (v1[i] != v2[i])
                    return false;
                i++;
            }
            return true;
        }
    }
    return false;
}

public int compareTo(String anotherString) {
    int len1 = value.length;
    int len2 = anotherString.value.length;
    int lim = Math.min(len1, len2);
    char v1[] = value;
    char v2[] = anotherString.value;

    int k = 0;
    while (k < lim) {
        char c1 = v1[k];
        char c2 = v2[k];
        if (c1 != c2) {
            return c1 - c2;
        }
        k++;
    }
    return len1 - len2;
}

a. From the source code, it is clear that, compareTo method compares two strings lexicographically (based on unicode value of each character in the strings), where as equals method checks whether two strings have same content or not.

b. str1.equals((String)null) return false, where as str1.compareTo((String)null) throws NullPointerException

App.java

package com.sample.app;

public class App {
    public static void main(String args[]) {
        String str1 = "Hello World";
        
        System.out.println("str1.equals((String)null) : " + str1.equals((String)null));
        System.out.println("str1.compareTo((String)null) : " + str1.compareTo((String)null));
    }
}

Output

str1.equals((String)null) : false

Exception in thread "main" java.lang.NullPointerException

    at java.lang.String.compareTo(String.java:1155)

    at com.sample.app.App.main(App.java:8)

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