Java The Complete Reference, Seventh Edition

352 Part I: The Java Language

}

// A subclass of Gen.

class Gen2 extends Gen<String> {

Gen2(String o) {

super(o);

}

// A String-specific override of getob().

String getob() {

System.out.print("You called String getob(): ");

return ob;

}

}

// Demonstrate a situation that requires a bridge method.

class BridgeDemo {

public static void main(String args[]) {

// Create a Gen2 object for Strings.

Gen2 strOb2 = new Gen2("Generics Test");

System.out.println(strOb2.getob());

}

}

In the program, the subclassGen2extendsGen, but does so using aString-specific version

ofGen, as its declaration shows:

class Gen2 extends Gen<String> {

Furthermore, insideGen2,getob( )is overridden withStringspecified as the return type:

// A String-specific override of getob().

String getob() {

System.out.print("You called String getob(): ");

return ob;

}

All of this is perfectly acceptable. The only trouble is that because of type erasure, the

expected form ofgetob( )will be

Object getob() { // ...

To handle this problem, the compiler generates a bridge method with the preceding signature

that calls theStringversion. Thus, if you examine the class file forGen2by usingjavap, you

will see the following methods:

class Gen2 extends Gen{

Gen2(java.lang.String);

java.lang.String getob();

java.lang.Object getob(); // bridge method

}