Review Questions

1. Write a java program to display your name on the command prompt
2. Write a java program to display numbers from 1-10 using a for loop
3. Write a java program to display numbers for a given range on the command prompt
   eg. Java NumDemo 12 30
   will display numbers starting from 12 to 30
4. write a java program to sort and display a given number series as user arguments, and also display the maximum and the minimum in the series.
5. Write a java program to find the mean and the median of a given number series as user arguments: (use two methods to find the two attributes and invoke them inside the main method)
6. Write a java program to find the mode of a given number series as user arguments.
7. Identify what are the java keywords from the followings
   a. abstract b. boolean c. interface d.public e. method f. subclasses
8. Which one of these lists contains only Java programming language keywords? (Choose one.)
   A. class, if, void, long, Int, continue
   B. goto, instanceof, native, finally, default, throws
   C. try, virtual, throw, final, volatile, transient
   D. strictfp, constant, super, implements, do
   E. byte, break, assert, switch, include
9. Which three are legal array declarations? (Choose three.)
   A. int [] myScores [];
   B. char [] myChars;
   C. int [6] myScores;
   D. Dog myDogs [];
   E. Dog myDogs [7];
10. Which will legally declare, construct, and initialize an array? (Choose one.)
    A. int [] myList = {“1”, “2”, “3”};
    B. int [] myList = (5, 8, 2);
    C. int myList [] [] = {4,9,7,0};
    D. int myList [] = {4, 3, 7};
    E. int [] myList = [3, 5, 6];
    F. int myList [] = {4; 6; 5};
11. What is the output of the following program

public class CharDemo{
    public static void main(String arg[]){
       char a = 'A';
       char b = (char)(a+1);
       System.out.println(a+b);
       System.out.println("a+b is "+a+b);
       int x = 75;
       char y = (char)x;
       char half = '\u00AC';
       System.out.println("Y is "+y+"and half is"+half);

       }
    } 

Wrte your answers in the comments area and submit

Sample solutions

1. public class NameDisplay{
    public static void main(String[] arg){
      System.out.println("Chaminda Wijesinghe");
    }
   }

Write the above program on a notepad and
Save the above program using the file name NameDisplay.java and filetype All Files
Open command prompt and compile the program using "Javac NameDisplay.java"
Run the program using  "Java DisplayName"

2. public class NumberDisplay{
   public static void main(String[] arg){
     for(int i=1;i<=10;i++){
       System.out.println(""+i);
       } // end of for loop
    } //end of main method
    } // end of the class

3. public class NumberDisplay2{
   public static void main(String[] arg){

   int i = Integer.parseInt(arg[0]);
   int j = Integer.parseInt(arg[1]);
 
   for(int x=i; x<=j; x++){
      System.out.println(""+x);
      }
  }
  }

Sample Java Programms

A program to display prime Numbers

public class prime{
private static boolean checkprime(int num)
 {
 boolean done = false;
 
  for(int i=2;i<num;i++)
  {
  if(num%i!=0)
    done=true;
  else
    return false;
  }
  return done;
 }
public static void main(String[] arg)
 {
 for(int i=2;i<=100;i++)
  {
  if(checkprime(i))
  {
  System.out.println("prime "+i);
  }
  }
 }
}
A program to implement a Calculator

import java.awt.*;
import java.awt.event.*;
import java.applet.*;
public class CalculatorApplet extends Applet implements ActionListener
{
private Button keysArray[];
private Panel keyPad;
private TextField lcdField;
private double result;
private boolean first;
private boolean foundKey;
static boolean clearText;
private int prevOperator;
public void init()
{
  lcdField = new TextField(20);
  keyPad = new Panel ();
  keysArray = new Button[17];
  result = 0.0;
  prevOperator = 0;
  first = true;
  clearText = true;
  //Set frame layout manager setLayout(new BorderLayout());
  lcdField.setEditable(false);
  //Create buttons
  for (int i = 0; i <=9; i++)
   keysArray[i] = new Button(String.valueOf(i));
   keysArray[10] = new Button("/");
   keysArray[11] = new Button("*");
   keysArray[12] = new Button("-");
   keysArray[13] = new Button("+");
   keysArray[14] = new Button("=");
   keysArray[15] = new Button(".");
   keysArray[16] = new Button("CLR");

   //Set panel layout manager
   keyPad.setLayout(new GridLayout (4,4));
   //Add button to keyPad panel
   for (int i = 7; i <=10; i++) //adds Button 7,8,9, and divide to Panel
    keyPad.add(keysArray[i]);
   for (int i = 4; i <6; i++) //adds buttons 4,5,6 to Panel
    keyPad.add(keysArray[i]);
   keyPad.add(keysArray[11]); //adds multiply button to Panel
   for (int i = 1; i <= 3;i++) //adds buttons 1,2 and 3 to Panel
    keyPad.add(keysArray[i]);
   keyPad.add(keysArray[12]);//adds minus button to Panel
   keyPad.add(keysArray[0]); //adds 0 key to Panel
   for (int i = 15; i >=13; i--)
    keyPad.add(keysArray[i]); //adds decimal point, equal, and addition keys Panel
    add(lcdField, BorderLayout.NORTH); //adds text field to top of Frame
    add(keyPad, BorderLayout.CENTER); //adds Panel to center of Frame
    add(keysArray[16], BorderLayout.EAST); //adds Clear key to right side of applet
    for(int i = 0; i < keysArray.length; i++)
     keysArray[i].addActionListener(this);
 }
 public void actionPerformed(ActionEvent e)
 {
   foundKey = false;
   //Search for the key pressed
   for (int i = 0; i < keysArray.length && !foundKey; i++)
   if(e.getSource() == keysArray[i]) //key match found
   {
     foundKey = true;
     switch(i)
     {
     case 0: case 1: case 2: case 3: case 4: //number buttons
     case 5: case 6: case 7: case 8: case 9: //0-9
     case 15:
     if (clearText)
     {
     lcdField.setText("");
     clearText = false;
  }
  lcdField.setText(lcdField.getText() +
  keysArray[i].getLabel());
  break;
  case 10:// divide button
  case 11:// multiply button
  case 12:// minus button
  case 13:// plus button
  case 14:// equal button
    clearText = true;
    if (first) // First operand
    {
    if(lcdField.getText().length()==0)
     result = 0.0;
    else
     result = Double.valueOf(lcdField.getText()).doubleValue();
  first = false;
                prevOperator = i; //save previous operator
     }
       else //second operand already enter, so calculator total
       {
   switch(prevOperator)
   {
   case 10: //divide Button
    result /= Double.valueOf(lcdField.getText()).
    doubleValue();
  break;
  case 11: //multiply Button
  result *= Double.valueOf(lcdField.getText()).
  doubleValue();
  break;
  case 12: //minus button
  result -= Double.valueOf(lcdField.getText()).
  doubleValue();
  break;
  case 13: //plus button
  result += Double.valueOf(lcdField.getText()).
  doubleValue();
  break;
    }
    lcdField.setText(Double.toString(result));
    if (i==14)//equal button
     first = true;
    else
     prevOperator = i; //save previous opetator
     }
     break;
     case 16://Clear button
     clearText = true;
     first = true;
     lcdField.setText("");
     result = 0.0;
     prevOperator = 0;
     break;
     }
     }
    }
   }
A program to display Candidate's preferencial votes as a Histogram
import javax.swing.*;
public class Histogram
     {
     public static void main( String args[] )
         {
         int n[] = { 19, 3, 15, 7, 11, 9, 13, 5, 17, 1 };
         String output = "";
       
         output += "Canidate No\tVotes\tHistogram";
       
         for ( int i = 0; i < n.length; i++ )
             {
             output += "\n" + i + "\t" + n[ i ] + "\t";
           
             for ( int j = 1; j <= n[ i ]; j++ ) // print a bar
             output += "*";
         }
       
         JTextArea outputArea = new JTextArea( 11, 30 );
         outputArea.setText( output );
       
         JOptionPane.showMessageDialog( null, outputArea,"Histogram Printing Program",JOptionPane.INFORMATION_MESSAGE );
       
         System.exit( 0 );
     }
}