Multi-methods for Java

View the Project on GitHub gustavcedersjo/multij


MultiJ provides multi-methods to Java.


Multi-methods are defined as methods in a Java interface with the annotation @Module.

interface Example {
    default int test(Object o) {
        return 1;
    default int test(String s) {
        return 2;

The multi-method test is invoked by first creating an instance of the module and then invoking any of the test methods on the instance. MultiJ will select the most specific method with respect to the runtime types of the arguments.

Example example = MultiJ.instance(Example.class);
Object o = "hello";
int x = example.test(o); // x = 2

Doing the same thing on a regular Java object would not generate the same result.

Example example = new Example() {};
Object o = "hello";
int x = example.test(o); // x = 1