Name: KEY CMPS 109 Quiz 2  January 28, 1999

This is a closed notes, closed book exam.

• Does the statement int[] x; create an array of integers? If yes, how many elements are in the array, if no, how do you create an array of 100 integers?

  No, it only creates a reference to an array.

  x = new int[100];
  

• Describe in words what the following program will do. Place your answer in the space to the right of the program.

  import java.awt.*;
  import java.applet.*;
  import java.awt.event.*;
   
  public class Quiz2Prob2 extends Applet 
      implements ActionListener
  {
    boolean first_pushed = false;
    Button first_button = new Button("Push Me First");
    Button second_button = new Button("Push Me Second");
    public void init()
    {
      first_button.addActionListener(this);
      second_button.addActionListener(this);
      add(first_button);
      add(second_button);
    }
    public void actionPerformed(ActionEvent e)
    {
      if(!first_pushed){
        if(e.getSource() == first_button)
          first_pushed = true;
  	repaint();// ADD THIS FOR SOLUTION TO THE NEXT PROBLEM
      }
      else if(e.getSource() == second_button)
        second_button.setLabel("Good Job!");
    }
  }
  

  The program creates two buttons. Nothing appears to change until the first time the button labeled ``Push Me Second'' is pushed AFTER the button labeled ``Push Me First'' is pushed. At that point the label on the button second_button changes to ``Good Job!'' 0.25in

• Modify the applet in the previous problem so that after clicking the button labeled ``Push Me First,'' a solid blue 50x50 pixel square will be drawn in the upper left corner of the applet and remain there. If you need to add a complete method, write it below, any other minor changes can be indicated directly in the code above. Hint: the method to actually do the drawing is called fillRectangle().

  public void paint(Graphics g)
  {
    if(first_pushed){
      g.setColor(Color.blue);
      g.fillRect(0,0,50,50);// Whoops it is fillRect not fillRectangle
    }
  }
  

• What does the following program print?

  // don't forget, array elements are initialized to 0 automatically
  class Quiz2Prob4 {
    public static void main(String[] args)
    {
      int[][] x;
      x = new int[4][];
      for(int i=0; i<x.length; i++)
        x[i] = new int[i*2];
      for(int i=0; i<x.length; i++){
        for(int j=0; j<x[i].length; j++)
          System.out.print(x[i][j]);
        System.out.println();
      }
    }
  }
  
  OUTPUT:
  
  <a blank line here>
  00
  0000
  000000
  

• The following program contains 3 syntax errors. Locate and describe each error, then modify the program so that the syntax errors are eliminated using as few character insertions and/or deletions as possible. Hint: This single program contains errors similar to the errors in the four syntax questions on the first quiz.

  class Quiz2Syntax {
    public static void main(String[] args)
    {
      int int_val = 1;
      double double_val = 1.1;
      Foo foo1 = new Foo(); //no no-arg constructor, pass a value here
      Foo foo2 = new Foo(10);
      System.out.println(foo1.value); // value is private change to just foo1
      System.out.println(foo2.fiddle(int_val,double_val)); // this call is ok as is
      System.out.println(name); // can't reference non-static var from static method
    }
  
    String name = "testing";  // make this static
  }
  
  class Foo {
    Foo(int x){ value = x; }
    private int value;  // could just make this non-private to fix foo1.value
    double fiddle(double x, double y){
      return value+x+y; // nothing wrong with this
    }
  }