如何在不使用字符串缓冲区类replace（）方法的情况下替换字符串中的字符？

Question

I need to make replace method that replaces the characters between start(inclusive) and end(exclusive, ie characters up to index end-1 will be replaced) in this TextLine with characters in the specified string fragment. I can not directly or indirectly use StringBuffer Class replace(int start, int end, String fragment) method. I'm trying to make the eLine.replace(0, 3, "abc"); or eLine.replace(0, 3, "abc"); work.

I tried to make a replace method similar to StringBuffer Class but it didn't work out. I can't think of another way to make a replace like that which is why I'm stuck. If there is another way, please show me an example or solution.

public int length;
public char[] characters;

public class TextLineTester {
  public static void main(String args[]) { 
     Scanner input = new Scanner(System.in);
     System.out.println("Enter a line of text.");
     String text = input.nextLine();
     EditableTextLine eLine = new EditableTextLine(text);
     Scanner strCharsInput = new Scanner(System.in);
     System.out.println("Enter string of characters.");
     String str = strCharsInput.nextLine();
     eLine.replace(0, 3, "abc");
     eline.replace(0, str.length(), "abc"); // suppose to replace all occurrences of string eLine with the string ”abc”and print the modified eLine
     System.out.println(eLine.toString());
  }  
}

public void replace(int start, int end, String fragment) {
     if (end > length) {
        end = length;
     }

     int fragmentLength = fragment.length();
     int newLength = length + fragmentLength - (end - start);
     ensureCapacityInternal(newLength);
     System.arraycopy(characters, end, characters, start + 
                                           fragmentLength, length - end);
     fragment.getChars(0,0, characters, start);
     length = newLength;
}

public EditableTextLine(String line) { // creates EditableTextLine object
   length = line.length();
   characters = new char[DEFAULT_SIZE * 2];
   characters = line.toCharArray();
}

public String toString() {
   return "Characters: " + new String(characters);
}

}

This is the error I get from this current replace method. 
  Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException
    at java.lang.System.arraycopy(Native Method)
    at edu.uga.cs1302.txtbuff.EditableTextLine.replace(EditableTextLine.java:109)
    at edu.uga.cs1302.test.TextLineTester.main(TextLineTester.java:36)


 Input: ABCDEFG
 After  eLine.replace(0, 3, "abc"), Output will be 
 Output: abcBCDEFG


 Another example:
 Input: AB678CDEFGHIJK12345
 eLine.replace(2,5,”XY”);  // line is now ”ABXYCDEFGHIJK12345”

Answer 1

For an isolated method to take any string and make the replacement, this would be the easiest.

   public static String replace(String orig, int start, int end, String replace) {
      String front = orig.substring(0,start);
      String back = orig.substring(end);
      return front + replace + back;
   }

I intentionally omitted using StringBuilder . This should be easy to adapt to a homegrown "String" class.