將字符串轉換爲字符與開關的情況下

Question

我正在從字符串中的用戶輸入，我想迭代和測試使用case語句，但它不工作。它不打印報表。

import java.io.*; 
import java.util.*; 

public class fh3 

{ 
    public static void main(String args[])throws IOException 

{ 

    String sentence = ""; 

    System.out.println("Enter the word : "); 
    Scanner scan = new Scanner(System.in); 
    String word = scan.next(); 


    char[] chars = word.toCharArray(); 

    for(int i = 0; i < word.length(); i++) 
    { 

     System.out.println("---" + chars[i]); 
     switch(chars[i]) 
     { 
      case 0: sentence = " "; 
       System.out.println("B"); 
       break; 
      case 1: sentence = "A"; 
       break; 
      case 2: sentence = "B"; 
       System.out.println("B"); 
       break; 
      case 3: sentence = "C"; 
       break; 


     } 
     sentence+=sentence; 
    System.out.println(sentence); 
    } 


} 

} 

如果我輸入20巢穴它應打印 「B」 但是它作爲

Enter the word : 
20 
---2 

---0 

那裏我得到錯誤的打印？

Answer 1

因爲你在字符，不是整數切換：

switch(chars[i]){ 
    case '0': sentence = " "; 
      System.out.println("B"); 
      break; 
    case '1': sentence = "A"; 
      break; 
    case '2': sentence = "B"; 
      System.out.println("B"); 
      break; 
    case '3': sentence = "C"; 
      break; 
} 

Answer 2

既然你正在做交換機上char類型，你的情況應該是相同的。在你的情況下，因爲你把整個值作爲整數值，它只是不匹配。 「0」是不等於0

switch(chars[i]) { 
    case '0': // switch on char '0' and not integer 0. 
    case '1': // switch on char '1' and not integer 1. 
    case '2': // switch on char '2' and not integer 2. 
    ... 
} 

Answer 3

您的開關被接受char但沒有合適的case是there.So其打印僅此語句System.out.println("---" + chars[i]);兩次（因爲word.length()返回2你的情況）

import java.io.*; 
import java.util.*; 

public class fh3 

{ 
    public static void main(String args[])throws IOException 

{ 

    String sentence = ""; 

    System.out.println("Enter the word : "); 
    Scanner scan = new Scanner(System.in); 
    String word = scan.next(); 


    char[] chars = word.toCharArray(); 

    for(int i = 0; i < word.length(); i++) 
    { 

     System.out.println("---" + chars[i]); 
     switch(chars[i]) 
     { 
      case '0': sentence = " "; 
       System.out.println("B"); 
       break; 
      case '1': sentence = "A"; 
       break; 
      case '2': sentence = "B"; 
       System.out.println("B"); 
       break; 
      case '3': sentence = "C"; 
       break; 


     } 
     sentence+=sentence; 
    System.out.println(sentence); 
    } 


} 

} 

Answer 4

在Java中，char類型通過Ascii table映射到int類型。

因此，如果您要檢查的字符'0'而不是NUL字符，你應該做的：

switch(chars[i]) { 
    case '0': // do the work 
    case '1': // do the work 
    // ... 
} 

Answer 5

import java.io.IOException; 
import java.util.Scanner; 

public class Fh3 { 
    public static void main(String args[]) throws IOException { 

     String sentence = ""; 
     System.out.println("Enter the word : "); 
     Scanner scan = new Scanner(System.in); 
     String word = scan.next(); 

     //Switch case needs you to compare the expression with constants hence the final keyword. 
     final char CHARONE = '1'; 
     final char CHARTWO = '2'; 
     final char CHARTHREE = '3'; 
     final char CHARFOUR = '4'; 

     char[] chars = word.toCharArray(); 

     for (int i = 0; i < word.length(); i++) { 
      System.out.println("---" + chars[i]); 
      switch (chars[i]) { 
       case 0: 
        sentence = " "; 
        System.out.println("B"); 
        break; 
       case CHARONE: 
        sentence = "A"; 
        break; 
       case CHARTWO: 
        sentence = "B"; 
        System.out.println("B"); 
        break; 
       case CHARTHREE: 
        sentence = "C"; 
        break; 

      } 
      sentence += sentence; 
      System.out.println(sentence); 
     } 
    } 
} 

你試圖比較字符詮釋..清除？