Topic: [新手求助]关于switch的用法

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1.[新手求助]关于switch的用法 Copy to clipboard
Posted by: nonamexz
Posted on: 2005-09-14 14:36

现在在自学JAVA,在网上找了本<<21天JAVA 2 自学通>>，已经看到第五天了，在完成书上布置的作业时我遇到了一些问题．
题目如下：

创建一个类，它读取从最开始的10个数字(one到ten）中的单词，并把它们转换成简单的long整数．使用switch语句来进行转换，并用命令行参数来给出要转换的单词．（题目在书中第99页）

1  class en2num
2  {
3      public static void main(String[] en)
4      {
5          int num;
6          if(en.length<=0)
7          {
8              System.out.println("缺少必要参数,请输入one到ten中的任一单词,形如:");
9              System.out.println("java en2num one");
10         }
11         else
12         {
13             switch(en[0])
14             {
15                 case "one":
16                     num=1;
17                 case "two":
18                     num=2;
19                 case "three":
20                     num=3;
21   ..........        
22             }
23         }
24     }
25 }


当我写到这里时，Eclipse开始报错了，出错位置是在第13行,出错提示:"case常量必须是char,byte,short或int,而不是String".
写到这里我真不知道应该怎么做了,如何才能让case的值为char,byte,short或int呢?

刚学编程,问的问题可能会很傻,请大家不要见笑.
2.Re:[新手求助]关于switch的用法 [Re: nonamexz] Copy to clipboard
Posted by: bluecrystal
Posted on: 2005-09-14 15:18

为什么非要用switch？
switch固然在很多场合比那种if...else形式的语句有效率
但是，我们也没必要一定要强行在你举的例子里面用switch吧。
Smile
3.Re:[新手求助]关于switch的用法 [Re: nonamexz] Copy to clipboard
Posted by: nonamexz
Posted on: 2005-09-14 16:15

书上要求用switch来进行处理的,我也知道这个问题用if-else来做的话会容易很多,但我也想知道用switch应该怎么去做,能否实现?
4.Re:[新手求助]关于switch的用法 [Re: nonamexz] Copy to clipboard
Posted by: why
Posted on: 2005-09-14 19:43

不能就是不能
如果不是一定要完成的話，就放棄這书上的要求
否則就當智力遊戲，用multiple case's：
只要讀第一個字母，有四個case's可以確定；再讀第二個字母，就搞定了
one
two three
four five
six seven
eight
nine
ten
相信閣下懂怎樣編寫吧．

注意，case 與 case 之間要有 break;
5.Re:[新手求助]关于switch的用法 [Re: nonamexz] Copy to clipboard
Posted by: nonamexz
Posted on: 2005-09-14 21:50

谢谢Why的点拔
呵呵，我也知道这个用if做会容易很多
我只想明白，如果不惜一切代价，是否真的可以用switch来实现Smile
6.Re:[新手求助]关于switch的用法 [Re: nonamexz] Copy to clipboard
Posted by: why
Posted on: 2005-09-14 22:43

nonamexz wrote:
谢谢Why的点拔
呵呵，我也知道这个用if做会容易很多
我只想明白，如果不惜一切代价，是否真的可以用switch来实现Smile

Now you know it's possible.
Please post your solution here when it's done.

Oops..
> 不能就是不能
What I meant is 不能让case的值为String

> 再讀第二個字母，就搞定了
should read
再讀第二個字母，use another switch-case，就搞定了
7.Re:[新手求助]关于switch的用法 [Re: nonamexz] Copy to clipboard
Posted by: nonamexz
Posted on: 2005-09-15 12:09

why,我已经把这道题目做出来了,这是我有史以来写过的最长的一个java程序啦.
Smile

class en2num
{
  public static void main(String[] en)  {
    
    long num=0;
    char charEn;    
    if(en.length<=0)
    {
      System.out.println("缺少必要参数,请输入one到ten中的任一单词,形如:");
      System.out.println("java en2num one");
    }
    else
    {
      charEn=en[0].charAt(0);
      switch(charEn)
      {
        case 'o':
          num=1;
          break;
        case 't':
          switch(en[0].charAt(1))
          {
            case 'w':
              num=2;
              break;
            case 'h':
              num=3;
              break;
            case 'e':
              num=10;
              break;
          }
          break;
        case 'f':
          switch (en[0].charAt(1))
          {
          case 'o':
            num=4;
            break;

          case 'i':
            num=5;
            break;
          }
          break;
        case 's':
          switch (en[0].charAt(1))
          {
          case 'i':
            num=6;
            break;

          case 'e':
            num=7;
            break;
          }
          break;
        case 'e':
          num=8;
          break;
        case 'n':
          num=9;
          break;        
      }
      System.out.println(num);
    }
  }
}
8.Re:[新手求助]关于switch的用法 [Re: nonamexz] Copy to clipboard
Posted by: bluecrystal
Posted on: 2005-09-15 15:00

通常情况下，类名首字母大写哈
9.Re:[新手求助]关于switch的用法 [Re: bluecrystal] Copy to clipboard
Posted by: nonamexz
Posted on: 2005-09-15 17:14

bluecrystal wrote:
通常情况下，类名首字母大写哈


嗯,记下来了,谢谢.
10.Re:[新手求助]关于switch的用法 [Re: nonamexz] Copy to clipboard
Posted by: beyond1984
Posted on: 2005-09-21 16:26

Don't u think it so boring???
you'd better use class to encapsulate the input string as follows:

public class B {
  public B() {
  }
  public static final int one = 1;            //*
  public static final int two = 2;            //*
  public static final int three = 3;          //*

  public static void main(String [] args){
    Enum e = new Enum("two"); //Enum e = new Enum(args[0]); all right.
    switch (e.getVal()){
      case one:                
        System.out.println(e.getVal());
        break;
      case two:
        System.out.println(e.getVal());
        break;
      case three:
        System.out.println(e.getVal());
        break;
      default:
        break;
    }
  }
}

class Enum{
  private int val = 0;
  public Enum(String str){
    if(str == "one"){            //*
      val = 1;
    }
    if(str == "two"){            //*
      val = 2;
    }
    if(str == "three"){         //*
      val = 3;
    }
  }
  public int getVal(){
    return val;
  }
}

But this is not a good way to use swich, you must be sure there should be a 'switch' rather than else.Anyway what i wrote is boring.too,since u should maintain the place with tag *, as to make them synchronized.
11.Re:[新手求助]关于switch的用法 [Re: nonamexz] Copy to clipboard
Posted by: beyond1984
Posted on: 2005-09-21 16:44


public class B {
  public B() {
  }
  public static void main(String [] args){
    Enum e = new Enum("two");
    switch (e.getVal()){
      case Enum.one:
        System.out.println(e.getVal());
        break;
      case Enum.two:
        System.out.println(e.getVal());
        break;
      case Enum.three:
        System.out.println(e.getVal());
        break;
      default:
        break;
    }
  }
}

class Enum{
  private int val = 0;
  public static final int one = 1;
  public static final int two = 2;
  public static final int three = 3;
  public Enum(String str){
    if(str == "one"){
      val = one;
    }
    if(str == "two"){
      val = two;
    }
    if(str == "three"){
      val = three;
    }
  }
  public int getVal(){
    return val;
  }
}
//Oh,sth changed,sth improved, right? U can only maintain the class Enum and
//make your code clear.Good luck.
12.Re:[新手求助]关于switch的用法 [Re: beyond1984] Copy to clipboard
Posted by: why
Posted on: 2005-09-21 19:07

beyond1984 wrote:

...
  public Enum(String str){
    if(str == "one"){
      val = one;
    }
    if(str == "two"){

Sad
use equals(), not ==

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