dOvs 2010

Consider the following program. Look at the generated bytecode for the method m (using javap -c Test). Can you generate better code by hand?

public class Test {
  static void m(int x) {
    System.out.print(x+x+x+x+1+2+3+4+5);
  }
  public static void main(String[] args) {
    m(42);
    m(87);
  }
}

mcode

Try to cheat the Java bytecode verifier in the following manners:
1. perform address arithmetic
2. pop something off an empty stack
3. construct two different types of stack (of the same height) in the branches of an if-else statement

Consider the following program. Does it output 1, 2, or 3? Look at the generated bytecode (using javap -c Test). Discuss the exact semantics of the invokevirtual instruction.

class A {
  int m(Object x, Object y) {
    return 1;
  }
}
class B extends A {
  int m(Object x, String y) {
    return 2;
  }
}
class C extends B {
  int m(Object x, Object y) {
    return 3;
  }
}
public class Test {
  public static void main(String[] args) {
    A a = new C();
    System.out.println(a.m(null,"abc"));
  }
}

maincode