使用字符串indexOf java

Question

im doing a program where i need to return the index of MyString of the first occurence. idk how to use the indexof in this situation. i think it might be something like ch = indexof[] but im not sure. im still new at this and the api didnt help me much

/*********************************************************************************
     This program will create classes that do similar operations to the Java String

     Javier Perez
     csc110
     11/5/12
    *********************************************************************************/
    package string.assignment;
    public class MyString
    {

        private char[] array;
        private int size;
        private int max;

        public MyString()
        {
            array = new char[25];
            max = 25;
        }
        public void setString(String newString)
        {
         if(newString.length() > 25)
         {
             System.out.println("/nEnter a number equal or less than 25 " );

         }
         else
         {
          for(int i=0; i < newString.length(); i++)
          {
            array[i] = newString.charAt(i);
          }
         }
        }


        public String toString()
        {
            return new String(array);
        }

        public char charAt(int index)
        {
            return array[index];
        }

        public boolean contains(char ch)
        {
            for(char c: array)
            {
                if(c == ch) return true;
            }
            return false;
        }
        public int indexOf( char ch )
        {
            ch = ch.indexOf();

        }
        return index; 


    }

Answer 1

For fetching the index of a certain character from your array, you would have to iterate over the array, and compare each character with the one you want to check. If any character matches, return the index immediately.

Also, your last return statement should be inside your method, else your code would not compile.

So, your indexOf method in its simplest would be like this: -

public int indexOf( char ch ) {
    for (int i = 0; i < array.length; i++) {
        if (array[i] == ch) {
            return i;   // Character found, return current index
        }
    }
    return -1;    // Character not found. Return -1
}

Answer 2

Iterate your array of characters, match the desired character against the character at index in the array. If match found, not the position in the index variable which has default value as -1 and break the loop. Return the index value from the method.

     public int indexOf( char ch ){
        int index = -1;
        for(int i=0; i < array.length; i++){
         if(array[i] == ch){
             index = i;//first match found, stop searching
             break;
         }
       }
       return index; 
     }

This way, it returns the first matching position of the character in the string's character array, otherwise returns -1 .

Answer 3

If it does indeed compile then your cut and paste is bad - what is that return index doing at the end?

Anyway - not I've used your own charAt rather than just a char compare.

    public int indexOf( char ch )
    {
        int result = -1;
        for(int i = 0; i <  size; i++) {
            if (charAt(i) == ch) {
                result = i;
                break;
            }
        }
        return result;

    }