可以通过标识（即。==）比较Java Method对象，还是必须使用equals（）？

Question

在Java中，可以通过标识（即。==）比较java.lang.reflect.Method对象的实例，还是必须使用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;
    }
}