listing 1
/* A program that uses the Vehicle class.  
  
   Call this file VehicleDemo.java  
*/  
class Vehicle {  
  int passengers; // number of passengers  
  int fuelcap;    // fuel capacity in gallons 
  int mpg;        // fuel consumption in miles per gallon 
}  
  
// This class declares an object of type Vehicle.  
class VehicleDemo {  
  public static void main(String args[]) {  
    Vehicle minivan = new Vehicle();  
    int range;  
  
    // assign values to fields in minivan 
    minivan.passengers = 7; 
    minivan.fuelcap = 16; 
    minivan.mpg = 21; 
  
    // compute the range assuming a full tank of gas 
    range = minivan.fuelcap * minivan.mpg; 
  
    System.out.println("Minivan can carry " + minivan.passengers + 
                       " with a range of " + range);  
  }  
}

listing 2
// This program creates two Vehicle objects. 
 
class Vehicle {  
  int passengers; // number of passengers  
  int fuelcap;    // fuel capacity in gallons 
  int mpg;        // fuel consumption in miles per gallon 
}  
  
// This class declares an object of type Vehicle.  
class TwoVehicles {  
  public static void main(String args[]) {  
    Vehicle minivan = new Vehicle();  
    Vehicle sportscar = new Vehicle();  
 
    int range1, range2;  
  
    // assign values to fields in minivan 
    minivan.passengers = 7; 
    minivan.fuelcap = 16; 
    minivan.mpg = 21; 
  
    // assign values to fields in sportscar 
    sportscar.passengers = 2; 
    sportscar.fuelcap = 14; 
    sportscar.mpg = 12; 
  
    // compute the ranges assuming a full tank of gas 
    range1 = minivan.fuelcap * minivan.mpg; 
    range2 = sportscar.fuelcap * sportscar.mpg; 
  
    System.out.println("Minivan can carry " + minivan.passengers + 
                       " with a range of " + range1);  
 
    System.out.println("Sportscar can carry " + sportscar.passengers + 
                       " with a range of " + range2);  
  }  
}

listing 3
// Add range to Vehicle. 
 
class Vehicle {  
  int passengers; // number of passengers  
  int fuelcap;    // fuel capacity in gallons 
  int mpg;        // fuel consumption in miles per gallon 
 
  // Display the range. 
  void range() { 
    System.out.println("Range is " + fuelcap * mpg); 
  } 
}  
  
class AddMeth {  
  public static void main(String args[]) {  
    Vehicle minivan = new Vehicle();  
    Vehicle sportscar = new Vehicle();  
 
    int range1, range2;  
  
    // assign values to fields in minivan 
    minivan.passengers = 7; 
    minivan.fuelcap = 16; 
    minivan.mpg = 21; 
  
    // assign values to fields in sportscar 
    sportscar.passengers = 2; 
    sportscar.fuelcap = 14; 
    sportscar.mpg = 12; 
  
 
    System.out.print("Minivan can carry " + minivan.passengers + 
                     ". "); 
 
    minivan.range(); // display range of minivan 
 
    System.out.print("Sportscar can carry " + sportscar.passengers + 
                     ". "); 
     
    sportscar.range(); // display range of sportscar. 
  }  
}

listing 4
void myMeth() { 
  int i; 
 
  for(i=0; i<10; i++) { 
    if(i == 5) return; // stop at 5 
    System.out.println(); 
  } 
}

listing 5
// Use a return value. 
 
class Vehicle {  
  int passengers; // number of passengers  
  int fuelcap;    // fuel capacity in gallons 
  int mpg;        // fuel consumption in miles per gallon 
 
  // Return the range. 
  int range() { 
    return mpg * fuelcap; 
  } 
}  
  
class RetMeth {  
  public static void main(String args[]) {  
    Vehicle minivan = new Vehicle();  
    Vehicle sportscar = new Vehicle();  
 
    int range1, range2;  
  
    // assign values to fields in minivan 
    minivan.passengers = 7; 
    minivan.fuelcap = 16; 
    minivan.mpg = 21; 
  
    // assign values to fields in sportscar 
    sportscar.passengers = 2; 
    sportscar.fuelcap = 14; 
    sportscar.mpg = 12; 
  
    // get the ranges 
    range1 = minivan.range(); 
    range2 = sportscar.range(); 
 
 
    System.out.println("Minivan can carry " + minivan.passengers + 
                     " with range of " + range1 + " Miles"); 
 
 
    System.out.println("Sportscar can carry " + sportscar.passengers + 
                     " with range of " + range2 + " miles"); 
     
  }  
}

listing 6
// A simple example that uses a parameter. 
 
class ChkNum {  
  // return true if x is even 
  boolean isEven(int x) { 
    if((x%2) == 0) return true;  
    else return false; 
  } 
}  
  
class ParmDemo {  
  public static void main(String args[]) {  
    ChkNum e = new ChkNum(); 
 
    if(e.isEven(10)) System.out.println("10 is even."); 
 
    if(e.isEven(9)) System.out.println("9 is even."); 
 
    if(e.isEven(8)) System.out.println("8 is even."); 
 
  }  
}

listing 7
class Factor { 
  boolean isFactor(int a, int b) { 
    if( (b % a) == 0) return true; 
    else return false; 
  } 
} 
class IsFact {  
  public static void main(String args[]) {    
    Factor x = new Factor(); 
 
    if(x.isFactor(2, 20)) System.out.println("2 is factor"); 
    if(x.isFactor(3, 20)) System.out.println("this won't be displayed"); 
 
  } 
}

listing 8
/* 
   Add a parameterized method that computes the  
   fuel required for a given distince. 
*/ 
 
class Vehicle {  
  int passengers; // number of passengers  
  int fuelcap;    // fuel capacity in gallons 
  int mpg;        // fuel consumption in miles per gallon 
 
  // Return the range. 
  int range() { 
    return mpg * fuelcap; 
  } 
 
  // Compute fuel needed for a given distance. 
  double fuelneeded(int miles) { 
    return (double) miles / mpg; 
  } 
}  
  
class CompFuel {  
  public static void main(String args[]) {  
    Vehicle minivan = new Vehicle();  
    Vehicle sportscar = new Vehicle();  
    double gallons; 
    int dist = 252; 
 
     // assign values to fields in minivan 
    minivan.passengers = 7; 
    minivan.fuelcap = 16; 
    minivan.mpg = 21; 
  
    // assign values to fields in sportscar 
    sportscar.passengers = 2; 
    sportscar.fuelcap = 14; 
    sportscar.mpg = 12; 
 
    gallons = minivan.fuelneeded(dist);  
  
    System.out.println("To go " + dist + " miles minivan needs " + 
                       gallons + " gallons of fuel."); 
     
    gallons = sportscar.fuelneeded(dist);  
  
    System.out.println("To go " + dist + " miles sportscar needs " + 
                       gallons + " gallons of fuel."); 
     
  }  
}

listing 9
/*  
   Project 4-1  
  
   Convert the help system from Project 3-3 into  
   a Help class. 
*/  
 
class Help { 
  void helpon(int what) { 
    switch(what) {  
      case '1':  
        System.out.println("The if:\n");  
        System.out.println("if(condition) statement;");  
        System.out.println("else statement;");  
        break;  
      case '2':  
        System.out.println("The switch:\n");  
        System.out.println("switch(expression) {");  
        System.out.println("  case constant:");  
        System.out.println("    statement sequence");  
        System.out.println("    break;");  
        System.out.println("  // ...");  
        System.out.println("}");  
        break;  
      case '3':  
        System.out.println("The for:\n");  
        System.out.print("for(init; condition; iteration)");  
        System.out.println(" statement;");  
        break;  
      case '4':  
        System.out.println("The while:\n");  
        System.out.println("while(condition) statement;");  
        break;  
      case '5':  
        System.out.println("The do-while:\n");  
        System.out.println("do {");  
        System.out.println("  statement;");  
        System.out.println("} while (condition);");  
        break;  
      case '6':  
        System.out.println("The break:\n");  
        System.out.println("break; or break label;");  
        break;  
      case '7':  
        System.out.println("The continue:\n");  
        System.out.println("continue; or continue label;");  
        break;  
    }  
    System.out.println();  
  } 
 
  void showmenu() { 
    System.out.println("Help on:");  
    System.out.println("  1. if");  
    System.out.println("  2. switch");  
    System.out.println("  3. for");  
    System.out.println("  4. while");  
    System.out.println("  5. do-while");  
    System.out.println("  6. break");  
    System.out.println("  7. continue\n");  
    System.out.print("Choose one (q to quit): ");  
  } 
 
  boolean isvalid(int ch) { 
    if(ch < '1' | ch > '7' & ch != 'q') return false; 
    else return true; 
  } 
 
} 
 
class HelpClassDemo {  
  public static void main(String args[])   
    throws java.io.IOException {  
    char choice;  
    Help hlpobj = new Help(); 
 
    for(;;) {  
      do { 
        hlpobj.showmenu();  
        do {  
          choice = (char) System.in.read();  
        } while(choice == '\n' | choice == '\r');      
 
      } while( !hlpobj.isvalid(choice) );  
  
      if(choice == 'q') break;  
  
      System.out.println("\n");  
   
 
      hlpobj.helpon(choice); 
    } 
  } 
}

listing 10
// A simple constructor. 
  
class MyClass { 
  int x; 
 
  MyClass() { 
    x = 10; 
  }   
}   
   
class ConsDemo {   
  public static void main(String args[]) {   
    MyClass t1 = new MyClass(); 
    MyClass t2 = new MyClass(); 
 
    System.out.println(t1.x + " " + t2.x); 
  }   
}

listing 11
// A parameterized constructor. 
  
class MyClass { 
  int x; 
 
  MyClass(int i) { 
    x = i; 
  }   
}   
   
class ParmConsDemo {   
  public static void main(String args[]) {   
    MyClass t1 = new MyClass(10); 
    MyClass t2 = new MyClass(88); 
 
    System.out.println(t1.x + " " + t2.x); 
  }   
}

listing 12
// Add a constructor.  
  
class Vehicle {   
  int passengers; // number of passengers   
  int fuelcap;    // fuel capacity in gallons  
  int mpg;        // fuel consumption in miles per gallon  
  
  // This is a constructor for Vehicle. 
  Vehicle(int p, int f, int m) { 
    passengers = p; 
    fuelcap = f; 
    mpg = m; 
  } 
 
  // Return the range.  
  int range() {  
    return mpg * fuelcap;  
  }  
  
  // Compute fuel needed for a given distance. 
  double fuelneeded(int miles) {  
    return (double) miles / mpg;  
  }  
}   
   
class VehConsDemo {   
  public static void main(String args[]) {   
 
    // construct complete vehicles 
    Vehicle minivan = new Vehicle(7, 16, 21);   
    Vehicle sportscar = new Vehicle(2, 14, 12);   
    double gallons;  
    int dist = 252;  
  
    gallons = minivan.fuelneeded(dist);   
   
    System.out.println("To go " + dist + " miles minivan needs " +  
                       gallons + " gallons of fuel.");  
      
    gallons = sportscar.fuelneeded(dist);   
   
    System.out.println("To go " + dist + " miles sportscar needs " +  
                       gallons + " gallons of fuel.");  
      
  }   
}

listing 13
/* 
   Project 4-2 
   Demonstrate the finalize() method. 
*/ 
   
class FDemo {  
  int x;  
  
  FDemo(int i) {  
    x = i;  
  }    
 
  // called when object is recycled 
  protected void finalize() { 
    System.out.println("Finalizing " + x); 
  } 
   
  // generates an object that is immediately destroyed 
  void generator(int i) { 
    FDemo o = new FDemo(i); 
  } 
 
}    
    
class Finalize {    
  public static void main(String args[]) {    
    int count; 
 
    FDemo ob = new FDemo(0); 
 
    /* Now, generate a large number of objects.  At 
       some point, garbage collection will occur.  
       Note: you might need to increase the number 
       of objects generated in order to force 
       garbage collection. */ 
 
    for(count=1; count < 100000; count++) 
      ob.generator(count);  
  }    
}

listing 14
class Pwr { 
  double b; 
  int e; 
  double val; 
 
  Pwr(double base, int exp) { 
    b = base; 
    e = exp; 
 
    val = 1; 
    if(exp==0) return; 
    for( ; exp>0; exp--) val = val * base; 
  } 
 
  double get_pwr() { 
    return val; 
  } 
} 
  
class DemoPwr { 
  public static void main(String args[]) {   
    Pwr x = new Pwr(4.0, 2); 
    Pwr y = new Pwr(2.5, 1); 
    Pwr z = new Pwr(5.7, 0); 
 
    System.out.println(x.b + " raised to the " + x.e +  
                       " power is " + x.get_pwr()); 
    System.out.println(y.b + " raised to the " + y.e +  
                       " power is " + y.get_pwr()); 
    System.out.println(z.b + " raised to the " + z.e +  
                       " power is " + z.get_pwr()); 
  } 
}

listing 15
class Pwr { 
  double b; 
  int e; 
  double val; 
 
  Pwr(double base, int exp) { 
    this.b = base; 
    this.e = exp; 
 
    this.val = 1; 
    if(exp==0) return; 
    for( ; exp>0; exp--) this.val = this.val * base; 
  } 
 
  double get_pwr() { 
    return this.val; 
  } 
}

listing 16
Pwr(double b, int e) { 
  this.b = b; 
  this.e = e; 
 
  val = 1; 
  if(e==0) return; 
  for( ; e>0; e--) val = val * b; 
}