What is a "bridge method" ?

Question

The 1.5 reflection API has boolean Method.isBridge()
The javadoc only says "returns true if and only if this method is a bridge method as defined by the Java Language Specification"..
But i can't find any JLS-3 specification or anything else to indicate what a Bridge Method is...
Do you know?

Answer 1

Bridge methods are compiler generated methods used to implement covariant result types and other instances involving generic types. Here is an example that was posted in the generics forum:
class Super<T> {
    public void foo(T t) {
        System.out.println("super");
class Sub extends Super<String> {
    @Override
    public void foo(String t)  {
        System.out.println("sub");
}Since the foo in the subclass has a different erasure, the compiler generates a bridge method that looks like this:
public void foo(Object t) {
    foo((String)t);
}This will ensure that the right method is called in this example:
Super<String> s = new Sub();
s.foo("Hello");This example would print "super" if the bridge method hadn't been there.