Can the Java Method object be compared by identity (ie. ==) or do I have to use equals()?

Question

In Java, can instances of the java.lang.reflect.Method object be compared by identity (ie. ==) or do I have to use equals()?

Answer 1

The question does not refer to the difference between == and equals in general, but refers to java.lang.reflect.Method instances in particular.

It is a reasonable question, because it could be justified to assume that there exists only one instance of each Method - similar to Class objects, which are created exactly once in the JVM.

However, this is not the case: Two Method objects may be equal, even though they are not identical, as can be seen in this example (it also does the comparison for Class objects, to emphasize that these indeed are identical)

package stackoverflow;

import java.lang.reflect.Method;

public class MethodEquals
{
    public static void main(String[] args) throws Exception
    {
        checkMethods();
        checkClasses();
    }

    static void checkMethods() throws Exception
    {
        Method m0 = MethodEquals.class.getMethod("exampleMethod", int.class);
        Method m1 = MethodEquals.class.getMethod("exampleMethod", int.class);

        boolean identical = (m0 == m1);
        boolean equal = m0.equals(m1);

        System.out.println("Methods: "+(identical == equal)); // prints "false"
    }

    static void checkClasses() throws Exception
    {
        Class<?> c0 = Class.forName("stackoverflow.MethodEquals");
        Class<?> c1 = Class.forName("stackoverflow.MethodEquals");

        boolean identical = (c0 == c1);
        boolean equal = c0.equals(c1);

        System.out.println("Classes: "+(identical == equal)); // prints "true"
    }

    public float exampleMethod(int i)
    {
        return 42.0f;
    }
}