add50.java

java 求1到50的和！通过获得键盘输入的选项

//Powered by Li Gang, 421341
//3.10 Make a program to add natural number 1 to 50 with 3 method

import java.io.*; 

//To count natural number 1+2+...+50
class Count {
      public static void addf(){                            //Use the "for" struct
	     int sum=0;
	     for(int i=1; i<=50; i++) { sum +=i; }
	     System.out.println("Great! 1+2+3+...+50 = "+sum);
       }
      public static void addw(){                            //Use the "while" struct
	     int i=1;   int sum=0;
	     while(i<=50) { sum +=i; i++; }
	     System.out.println("Great! 1+2+3+...+50 = "+sum);
       }
      public static void addd(){                            //Use the "do-while" struct
	     int i=1;   int sum=0;	
	     do { sum +=i; i++; } while(i<=50);
	     System.out.println("Great! 1+2+3+...+50 = "+sum);
       }
 }

//To get value of the key from the keyboard
class Get { 
      public static int readInt() {return Integer.parseInt(readStr());} 
      public static String readStr(){ 
             BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); 
             String str=" "; 
             try {str=br.readLine();} 
             catch (IOException ex) {System.out.println(ex);} 
             return str; 
       } 
 }

//the primary class
class add50 { 
      public static void main(String []args){    
             System.out.println("\n===========Use the follow 3 methods to add natural number 1 to 50==========="+"\n");
             System.out.println("                     1.  Use the struct for                           ");
             System.out.println("                     2.  Use the struct while                         ");        
             System.out.println("                     3.  Use the struct do-while                      "+"\n");
             System.out.println("===================Please input ,then press the key Enter===================");
             System.out.print("Option:  "); 
             int a; a=Get.readInt();         //Move the value of the key from the keyboard to var a
             switch(a){
                    case 1: Count.addf(); break;
                    case 2: Count.addw(); break;
                    case 3: Count.addd(); break;
              }         
       }  
 }