Why Objects.equals Handles Nulls Safely: A Deep Dive into Java Equality

I originally thought this method was introduced in Java 8, but it actually dates back to Java 1.7, so I examined the source code.

1. When the value is null

1. a.equals(b) throws a NullPointerException if a is null. 2. a.equals(b) returns false when a is non‑null and b is null. 3. Objects.equals(a, b) returns true if both are null, false if exactly one is null, and never throws an exception.

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. When the value is an empty string

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

"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

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.
     * If both arguments are null, true is returned; if exactly one is null, false is returned.
     * Otherwise equality is determined by calling a.equals(b).
     */
    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 is true it returns true immediately. 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)

When a and b are objects, a==b compares their references and returns true only if they point to the same heap object. a.equals(b) performs logical comparison of content; for custom classes it should be overridden to define logical equality.