what is super?

[scottie zman]

Hi all, I'm waiting for amazon to deliver the books... meanwhile, I have a java project to create!
Here is some code I found for a database access bean. Can someone please explain what the super() call does and why there is a method in the class with the same name as the class? Is that a requirement in a bean?
muchos thankyous,
Scottie Zman
---------------------------------------------
package sqlBeans;
import java.sql.*;
import java.io.*;
public class DbBean {
String dbURL;
String dbDriver;
private Connection dbConn;

public DbBean(){
super();
}

public boolean connect() throws ClassNotFoundException,SQLException {
Class.forName(dbDriver);
dbConn = DriverManager.getConnection(dbURL);
return true;
}

public void close() throws SQLException{
dbConn.close();
}

public ResultSet execSQL(String strSQL) throws SQLException{
Statement stmt = dbConn.createStatement();
ResultSet rs = stmt.executeQuery(strSQL);
return (rs == null) ? null : rs;
}

public int updateSQL(String strSQL) throws SQLException{
Statement stmt = dbConn.createStatement();
int r = stmt.executeUpdate(strSQL);
return (r == 0) ? 0 : r;
}
}

[This message has been edited by scottie zman (edited August 23, 2001).]

[David Weitzman]

There is no good reason for the super() call to be used like that. It would be automatically called if you left it out. Even then it doesn't do much. super(arguments) calls a contructor on a parent class. In this case that class would be java.lang.Object. Here is an example of it's use:

public class SuperClass {
  int id;
 
  // no argument constructor
  public SuperClass() {
    this.id = 30;
  }
 
  public SuperClass(int id) {
    this.id = id;
  }
 
  public void printId() {
    System.out.println("My id is " + id);
  }
}
 
public class SubClass extends SuperClass {
  String name;
 
  public SubClass(String name) {
    // implicit call to SuperClass no argument constructor
    // so id = 30
    this.name = name;
  }
 
  public SubClass(String name, int id) {
    super(id); // call to other SuperClass constructor
    // id = passed id
    this.name = name;
  }
 
  // override SuperClass.printId
  public void printId() {
    System.out.println("My name is " + name);
 
    // even though I've overrided SuperClass.printId(),
    // I can still call it.
    super.printId(); // prints 'My id is ' + id
  }
}
 
public class Test {
  public static void main(String[] args) {
    SuperClass spc = new SuperClass();
    SubClass   sbc = new SubClass("John");
    System.out.println("Super with default constructor:");
    spc.printId();
    System.out.println("Subclass with default constructor:");
    sbc.printId();
    spc = new SuperClass(20);
    sbc = new SubClass("John", 20);
    System.out.println("Super with 20:");
    spc.printId();
    System.out.println("Subclass with 20:");
    sbc.printId();
  }
}

[scottie zman]

Thanks for the explanation and example, it helped a lot!