What is the difference between the equals() and == operators in Java?

In Java, the equals() method is used to compare the equality of two objects based on their content, while the == operator is used to compare the references of two objects to see if they point to the same memory location. The main differences are:

• The equals() method can be overridden by a class to define its own equality criteria, whereas the == operator cannot be overridden.
• The equals() method compares the values of objects, whereas the == operator compares the memory addresses.
• By default, the equals() method compares the memory addresses similar to the == operator unless it is overridden.

Code Example

public class Main {
    public static void main(String[] args) {
        String str1 = "Hello";
        String str2 = new String("Hello");
        String str3 = str1;
        
        System.out.println(str1.equals(str2)); // Output: true
        System.out.println(str1 == str2); // Output: false
        
        System.out.println(str1.equals(str3)); // Output: true
        System.out.println(str1 == str3); // Output: true
        
        Integer num1 = 5;
        Integer num2 = 5;
        
        System.out.println(num1.equals(num2)); // Output: true
        System.out.println(num1 == num2); // Output: true
        
        Integer num3 = 200;
        Integer num4 = 200;
        
        System.out.println(num3.equals(num4)); // Output: true
        System.out.println(num3 == num4); // Output: false
    }
}

Output

true
false
true
true
true
true
true
false

Code Explanation

In this example, we have variables str1, str2, and str3 representing strings, and variables num1, num2, num3, and num4 representing integers.

When comparing strings using the equals() method, it compares the content of the strings. In the example, str1.equals(str2) returns true because the content of both strings is “Hello”. However, when using the == operator to compare the string objects themselves, str1 == str2 returns false because they refer to different memory locations.

When comparing references using the == operator, it checks whether the variables refer to the same object in memory. In the example, str1 == str3 returns true because both variables reference the same “Hello” string object in memory.

Similarly, when comparing Integer objects using the equals() method, it compares the values of the integers. In the example, num1.equals(num2) returns true because both variables have the value 5. However, when using the == operator to compare the Integer objects, num1 == num2 returns true because the values fall within the range of cached Integer objects.

For larger integer values, as seen in num3 and num4, the == operator returns false because the values are outside the range of cached Integer objects, even though num3.equals(num4) returns true because the values are equal.

This example highlights that the equals() method compares the content or values of objects, while the == operator compares the references or memory addresses of objects.