Why a.equals(b) Can Crash but Objects.equals(a,b) Won’t – Java Equality Explained

1. When values are null

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

2. a.equals(b) where a is not null but b is null returns false.

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

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

2. When values are empty strings

If both a and b are empty strings ( ""), a.equals(b) returns true; otherwise it returns false. Objects.equals behaves identically.

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

3. Source code analysis

Source

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

    public static boolean equals(Object a, Object b) {
        return (a == b) || (a != null && a.equals(b));
    }
}

Explanation

The method first checks reference equality ( a == b). If that fails, 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; it returns true only when both references point to the same heap object. a.equals(b) performs logical comparison based on the object's content; it can be overridden to provide meaningful equality semantics.