Comparing enum members in Java

In Java, an enum is a special data type used to define a fixed set of constants. It is a special kind of Java class that can contain constants, methods and variables, where each enum constant represents a single, unique instance

• Enum constants can be compared using the == operator or the equals() method.
• The equals() method internally uses ==.
• The == operator is preferred because it provides compile-time type safety and avoids NullPointerException.

Key Differences

1. Null Safety

• == never throws NullPointerException
• equals() throws NullPointerException if called on a null reference

2. Type Safety

• == performs compile-time type checking
• equals() does not check type compatibility at compile time

Example 1: Comparing Enum Constants Using == and equals()

This example shows how enum constants are compared using the == operator and the equals() method in different scenarios.

Java

enum Status {
    ACTIVE,
    INACTIVE
}
public class GFG {
    public static void main(String[] args) {
        Status s1 = Status.ACTIVE;
        Status s2 = Status.ACTIVE;
        Status s3 = null;

        System.out.println(s1 == s2);   // true
        System.out.println(s1 == s3);   // false
        System.out.println(s1.equals(s2)); // true

        // This will throw NullPointerException
        System.out.println(s3.equals(s1));
    }
}

Output:

true
false
true
Exception in thread "main" java.lang.NullPointerException

Explanation:

• s1 == s2: true because both refer to the same enum constant.
• s1 == s3: false; the == operator safely handles null.
• s1.equals(s2): true because both constants are equal.
• s3.equals(s1) : throws NullPointerException because equals() is called on a null reference.

Example 2: Type Safety in Enum Comparison

This example shows that == enforces compile-time type safety for enums, while equals() allows comparison and returns false for different enum types.

Java

enum Month {
    JAN, FEB
}
enum Day {
    MON, TUE
}
public class EnumTypeSafety {
    public static void main(String[] args) {
        Month m = Month.JAN;
        Day d = Day.MON;

        System.out.println(m.equals(d)); // false
        System.out.println(m == d); // Compilation error: incomparable types
    }
}

Output:

false
Compilation error: incomparable types: Month and Day

Explanation:

• m.equals(d) compiles and prints false because the enum types are different.
• m == d causes a compile-time error because == enforces strict type safety and does not allow comparison between different enum types.