listing 1
/* 
   This is a simple Java program. 
 
   Call this file Example.java. 
*/ 
class Example { 
  // A Java program begins with a call to main(). 
  public static void main(String args[]) { 
    System.out.println("Java drives the Web."); 
  } 
}

listing 2
/*   
   This demonstrates a variable.  
 
   Call this file Example2.java.  
*/   
class Example2 {   
  public static void main(String args[]) {   
    int var1; // this declares a variable  
    int var2; // this declares another variable  
  
    var1 = 1024; // this assigns 1024 to var1  
  
    System.out.println("var1 contains " + var1);   
  
    var2 = var1 / 2;  
  
    System.out.print("var2 contains var1 / 2: ");  
    System.out.println(var2);  
  }   
}

listing 3
/*  
   This program illustrates the differences 
   between int and double. 
 
   Call this file Example3.java. 
*/  
class Example3 {  
  public static void main(String args[]) {  
    int var;  // this declares an int variable 
    double x; // this declares a floating-point variable 
 
    var = 10; // assign var the value 10 
    
    x = 10.0; // assign x the value 10.0 
 
    System.out.println("Original value of var: " + var); 
    System.out.println("Original value of x: " + x); 
 
    System.out.println(); // print a blank line 
 
    // now, divide both by 4 
    var = var / 4;  
    x = x / 4; 
 
    System.out.println("var after division: " + var); 
    System.out.println("x after division: " + x); 
  }  
}

listing 4
/*  
   Project 1-1 
 
   This program converts gallons to liters. 
 
   Call this program GalToLit.java. 
*/  
class GalToLit {  
  public static void main(String args[]) {  
    double gallons; // holds the number of gallons 
    double liters;  // holds conversion to liters 
 
    gallons = 10; // start with 10 gallons 
 
    liters = gallons * 3.7854; // convert to liters 
 
    System.out.println(gallons + " gallons is " + liters + " liters."); 
  }  
}

listing 5
/*  
  Demonstrate the if.  
  
  Call this file IfDemo.java.  
*/  
class IfDemo {  
  public static void main(String args[]) {  
    int a, b, c;  
  
    a = 2;  
    b = 3;  
  
    if(a < b) System.out.println("a is less than b"); 
 
    // this won't display anything  
    if(a == b) System.out.println("you won't see this");  
 
    System.out.println(); 
 
    c = a - b; // c contains -1 
 
    System.out.println("c contains -1"); 
    if(c >= 0) System.out.println("c is non-negative"); 
    if(c < 0) System.out.println("c is negative"); 
 
    System.out.println(); 
 
    c = b - a; // c now contains 1 
    System.out.println("c contains 1"); 
    if(c >= 0) System.out.println("c is non-negative"); 
    if(c < 0) System.out.println("c is negative"); 
 
  }  
}

listing 6
/* 
  Demonstrate the for loop. 
 
  Call this file ForDemo.java. 
*/ 
class ForDemo { 
  public static void main(String args[]) { 
    int count; 
 
    for(count = 0; count < 5; count = count+1) 
      System.out.println("This is count: " + count); 
 
    System.out.println("Done!"); 
  } 
}

listing 7
/* 
  Demonstrate a block of code. 
 
  Call this file BlockDemo.java. 
*/ 
class BlockDemo { 
  public static void main(String args[]) { 
    double i, j, d; 
 
    i = 5; 
    j = 10; 
 
    // the target of this if is a block 
    if(i != 0) { 
      System.out.println("i does not equal zero"); 
      d = j / i; 
      System.out.print("j / i is " + d); 
    } 
  } 
}

listing 8
/*  
   Project 1-2 
 
   This program displays a conversion  
   table of gallons to liters. 
 
   Call this program "GalToLitTable.java". 
*/  
class GalToLitTable {  
  public static void main(String args[]) {  
    double gallons, liters; 
    int counter; 
 
    counter = 0; 
    for(gallons = 1; gallons <= 100; gallons++) { 
      liters = gallons * 3.7854; // convert to liters 
      System.out.println(gallons + " gallons is " + 
                         liters + " liters."); 
 
      counter++; 
      // every 10th line, print a blank line        
      if(counter == 10) { 
        System.out.println(); 
        counter = 0; // reset the line counter 
      } 
    } 
  }  
}