helpclassdemo.java

Mcgraw-Hill - Java 2 - A Beginner S Guide, 2Nd Ed - 2003 -prog.

/*  
   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); 
    } 
  } 
}