字符串索引超出範圍異常，在if else語句上

Question

問題代碼如下，如果您需要整個主要方法來幫助我，請詢問。該代碼符合但未按預期運行。如果數字超出/大於源文本的最後一個位置（這是用戶輸入的字符串），我試圖使代碼報告返回一個感嘆號，因此無法預定義該長度。異常是'StringIndexOutOfBoundsException'

TDLR num是一個int，sourcetext是一個字符串，兩者都是輸入。例外：當代碼輸出'！'時代替。

import java.util.Scanner; 

public class Temp { 

    public static void main(String[] args) { 

     Scanner sc; 
     int result, num= 0, end = -2, temp, infolost, count; 
     String word, sourcetext, answer, space= " "; 
     String sourcetext2, temp2; 
     char input, result2, chalost; 
     sc = new Scanner(System.in); 

     System.out.println("please enter sourcetext"); 
     sourcetext = sc.nextLine(); // user inputs source text 
     sourcetext = sourcetext.toLowerCase(); // converts sourcetext into lowercase      
     System.out.print("Would you like to 1 encrypt, or 2 decrypt?"); 
     answer = sc.next(); // user inputs choice 

     if (answer.equals("1")||(answer.equals("encrypt"))) { 

      System.out.println("Please enter at least one word to encrypt"); 
      word = sc.next(); // user inputs one word 

      for (int i= 0; i < word.length(); i++) { 
       temp = sourcetext.indexOf(word.charAt(i)); // uses index to convert char positions int num 
       System.out.print(space + temp + space);   
      } 
      System.out.print(space + end); 
     } 
     else if (answer.equals("2")||(answer.equals("decrypt"))) { 

      System.out.println("Please enter digits, with one space between each. End with -2");     
      while (num > -2) { 
       num = sc.nextInt(); // num to decrypt 
       if (num > -2) {  
        result2 = sourcetext.charAt(num); // num converted into characters 
        System.out.print(result2); 
       } else if (num > sourcetext.length()) { 
        System.out.print("!"); 
       } else if (num<0) { 
        System.out.print("end"); 
       } 
      } 
     } 
    } 
} 

Answer 1

這可能導致IndexOutOfBounds異常 - 因爲-1比-2更大 - 但還是出界...

if (num > -2){  
    result2 = sourcetext.charAt(num); // num converted into characters 
    System.out.print(sourcetext.indexOf(num)); 
} 

編輯：除非用戶輸入是-2 - 第一個if - 陳述將始終運行...您可能需要重新工作那裏的邏輯。編號2：如果num是-1sourcetext.charAt(num);導致IndexOutOfBounds。做類似

if(num == -2) { 
    System.out.print("end"); 
} else if (num >= 0 && num < sourcetext.lenght()) { 
    // index ok 
    result2 = sourcetext.charAt(num); // num converted into characters 
    System.out.print(result2); 
} else { 
    // index out of bounds 
    System.out.print("!"); 
} 

Answer 2

試試這樣說：

int stringLength = sourcetext.length(); 

if (num > stringLength) { 
    System.out.print("!"); 
} 
else if (num<0) { 
    System.out.print("end"); 
}