Write a function that will sort a string array using Java

First of all a, e and g are variables and not necessarily strings. What you mean is probably "a", "e" and "g".

Your question is essentially:

How do I sort the values in a String[] so that numbers are sorted numerically and prioritized before letters (or words?) which are sorted alphabetically?

Your question seems incomplete, though. How would you sort strings like "15qwe" or "asd34"? Since these could be interpreted in different ways and you haven’t told us the rules for these I will ignore these and help you with the case of only numbers and only letters.

There is a class called Integer that has a static method called parseInt(). If the argument to this method does not contain any integers it will throw an exception, so it is a simple way for you to check if it is a number or letter.

For example:

String[] arr = {"5", "7", "a", "1", "g", "b"};
String[] numberArray = new String[3];
// keep this as a String[] for simpler concatenation of the arrays later

String[] stringArr = new String[3];

/*if you do not know that there will be exactly 3 of each, 
  just write arr.length isntead of 3*/

for(int i = 0; i < arr.length; i++) {
    int numberIndex = 0;
    int stringIndex = 0;
    try {
        Integer.parseInt(arr[i]);
        numberArray[numberIndex] = arr[i];
        numberIndex++;
    } catch (Exception e) {
        String s = arr[i];
        stringArr[stringIndex] = s;
        stringIndex++;
    }
}
Arrays.sort(stringArr);
Arrays.sort(numberArray);

Now all you have to do is to concatenate the two arrays into one.

// you can replace numberArray.length and stringArr.length with 3 if you want
for(int i = 0; i < numberArray.length; i++) {
    arr[i] = numberArray[i];
}
for(int i = 0; i < stringArr.length; i++) {
    arr[numberArray.length + i] = stringArr[i];
}

System.out.println(Arrays.toString(arr));

Mistake found:

Since the numberArray is a String[] it will still sort alphabetically and not numerically. If you for example have "3", "1" and "15", it will sort them in this order: {"1", "15", "3"}. This is probably not what you want, so it was a mistake on my part to have a String[] instead of an int[].

So what you need to do is to implement these changes to the code:

  • int[] numberArray = new int[3]; instead of String[] numberArray = new String[3];

  • numberArray[numberIndex] = Integer.parseInt(arr[i]); instead of: Integer.parseInt(arr[i]); numberArray[numberIndex] = arr[i];

When you are going to concatenate the arrays later, you need to convert the integers to strings again. This is easily done with the static method Integer.toString().

So you need to make this small change to the code as well:

arr[i] = Integer.toString(numberArray[i]); instead of arr[i] = numberArray[i];

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