Language query

Question

The following compiles correctly:
import java.util.*;
public class MyVector extends Vector {
However,
import java.io.*;
public class MyPs extends PrintWriter {
gives the following error:
C:\LocalJava\Webserver\MyPs.java:3: cannot resolve symbol
symbol : constructor PrintWriter ()
location: class java.io.PrintWriter
public class MyPs extends PrintWriter {
^
1 error
I don't understand.
Paul Hide

Answer 1

Hi,
let's see what the compiler does.
1. It checks if you have a constructor defined. If not, a standard constructor is provided.
2. In this standard constructor super() is called.
So, MyVector compiles 'cause the class Vector has a standard constructor. MyPs does not compile 'cause PrintWriter has no standard constructor. This is what the error message says: It cannot find the constructor PrintWriter().
To make the second class compile, you have to provide your own constructor which calls one of the PrintWriter's constructors via super.
Andre