import java.applet.*;
import java.awt.*;
public class HiApplet
  extends Applet
{
  private String[] messages =
    {"Hello", "Hi", "How Are You?", "What's New?"};
  private int index = 0;
  public void init()
  {
    add(new MsgButton(this));
  }
  public void paint(Graphics g)
  {
    g.drawRect(0,0,size().width-1,size().height-1);
  }
  public boolean mouseDown(Event e, int x, int y)
  {
    getGraphics().drawString(messages[index], x, y);
    return true;
  }
  void changeMessage()
  {
    index = (index + 1) % messages.length;
  }
}
class MsgButton
  extends Button
{
  HiApplet parent;
  public MsgButton(HiApplet parent)
  {
    super("Change Message");
    this.parent = parent;
  }
  public boolean action(Event e, Object label)
  {
    parent.changeMessage();
    return true;
  }
}

public static void main(String argv[]) {...}

public class Echo
{
  public static void main(String argv[])
  {
    for (int i=0; i<argv.length; i++)
      System.out.print(argv[i] + " ");
    System.out.print("\n");
  }
}

System.exit(0);

String homedir = System.getProperty("user.home");
String debug = System.getProperty("myapp.debug");

% java -Dmyapp.debug=true myapp

package games.poker; // always the first declaration in a file

setenv CLASSPATH  .:~/classes:/usr/local/classes

edu.uci.ics.catalina.my_pack.my_class.display();

import java.util; // can access util.Hashtable

import java.util.Hashtable; // can access Hashtable

import java.util.*; // can access all classes within util

import java.lang.*;

/* This is a (potentially) multi-line comment */
// This is a single line comment
/** This is a special documentation comment */

public final class Math {
  public static final double PI = 3.14159;
}

\uxxxx  // where xxxx is four hexidecimal digits for the code

\n \r \t etc.

Button a = new button("On");
Button b = new button("Off");
a = b; // now both a and b refer to object labelled Off
int x = 1;
int y = 2;
x = y; // now x and y both have the value 2, but they have distinct storage

Vector v1 = new Vector;
Vector v2 = v1.clone(); // v2 is a deep copy of v1

if (v1.equals(v2)) // they are equal!

String s = "This is a string";

ComplexNumber c = new ConmplexNumber(1.0,0.0);
double magnitude = c.magnitude();

Button buttons[] = new Button[10];
for (int i=0; i<buttons.length; i++)
  buttons[i] = new Button("label " + i); // must allocate elements
int table[] = {1, 2, 4, 8, 16, 32, 128, 256}; // also allocates an array

table[8] // throws IndexOutOfBoundsException

object instanceof type

s1 + s2 + i   // converts non-String to String first, via toString method

i >>> 1

while (p != null)  ...
if (i != 0) ...

int i, j;
for (i=0, j=1; i*j < 100; i++, j--) ...
int a[] = {0,1,2,3,4,5,6,7,8,9};
for (int k=0; k<a.length; k++)
  System.out.println("a[" + k + "] = " + a[k]);
// like C++, scope of k is within loop

outer:for (...)
  for (...)
    break outer;

try
  // this statement execute, if an exception is thrown, its caught below
catch (SomeException e)
  // come here if SomeException is thrown
catch (OtherException e)
  // come here if OtherException is thrown
finally
  // always excute this statement no matter how we leave the try block

public void open_file() throws SomeException, OtherException {
  throw new SomeException("Oops!");
}