Why Objects.equals Beats a.equals in Java: Null Safety and Source Code Explained

1. Null values

1. a.equals(b) when a is null throws NullPointerException.

2. a.equals(b) when a is not null and b is null returns false.

3. Objects.equals(a, b) returns true if both are null, false if exactly one is null, and never throws NullPointerException.

null.equals("abc")    → throws NullPointerException
"abc".equals(null)    → returns false
null.equals(null)     → throws NullPointerException
Objects.equals(null, "abc") → returns false
Objects.equals("abc", null) → returns false
Objects.equals(null, null) → returns true

2. Empty string values

If both a and b are empty strings (""), a.equals(b) returns true; otherwise it returns false. Objects.equals behaves the same in these cases.

"abc".equals("") → returns false
"".equals("abc") → returns false
"".equals("")    → returns true
Objects.equals("abc", "") → returns false
Objects.equals("", "abc") → returns false
Objects.equals("", "")   → returns true

3. Source code analysis

1. Source

public final class Objects {
    private Objects() {
        throw new AssertionError("No java.util.Objects instances for you!");
    }

    /**
     * Returns true if the arguments are equal to each other
     * and false otherwise.
     * Consequently, if both arguments are null, true is returned
     * and if exactly one argument is null, false is returned.
     * Otherwise, equality is determined by using the Object.equals method
     * of the first argument.
     */
    public static boolean equals(Object a, Object b) {
        return (a == b) || (a != null && a.equals(b));
    }
}

2. Explanation

The method first checks reference equality ( a == b); if true, it returns true without further checks. If not, it ensures a is not null before invoking a.equals(b), which prevents a NullPointerException.

4. Difference between a==b and a.equals(b)

a==b

compares object references and returns true only when both references point to the same object in memory. a.equals(b) performs logical comparison based on the object's content; it returns true when the objects are considered equal, and typically requires overriding to provide meaningful equality logic.