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I am trying take a string similar to this: 3A5o2n4t and expand it back to a string like this: AAAooooonntttt (the number in front of the letter is how many times the letter repeats)
I was trying to use Integer.parseInt() to get the number in front of the letter, but it grabs all of the numbers. Is there a way to grab one number at a time? Also, does my code look okay after that issue is resolved? Or am I missing a bit still?

public String runLengthDecoding(String str3) 
 String convert = "";
 int number = 0;
 if (! str3.isEmpty()) 
 convert = str3.charAt(0) + "";
 
 for (int i = 0; i <= str3.length() - 1; i++) 
 if (Character.isDigit(str3.charAt(i))) //true or false, the current character is a digit
 String temp = "" + str3.charAt(i); //if true, make that character a string
 number = Integer.parseInt(temp); /*now store that character as a number (but I only want the current
 number, not all the numbers in the string*/
 System.out.println(number); /*Testing to see what number is, which is where I found it was 
 storing all the numbers */
 String temp2 = str3.charAt(i + 1) + ""; //Its supposed to start making a string that prints the character in front of it
 convert = temp2.repeat(number); //it will print the character however many times that number was stored as
 

 
 return convert;
 

Also I have not yet learned how to use arrays, that is why I am not using an array.

Edited to:

- accommodate strings that has length more then 1. Example: 10AA

- accommodate input that starts with a string. Example: A5o

To solve this you have to get all the simultaneous digits, example if you have "55s", you have to get "55", That is why your code is incorrect since if you parseInt whenever you see a digit then it will immediately parse into 5, but the actual number is 55, thus you should accumulate the simultaneous digits first and only parseInt when you encounter the first non digit.

Refer to the code and comments for details:

public class Main 
 public static void main(String[] args) 
 System.out.println("Input: 3A5o2n4t => Output : " + runLengthDecoding("3A5o2n4t"));
 System.out.println("Input: 3AA5o2n4t => Output : " + runLengthDecoding("3AA5o2n4t"));
 System.out.println("Input: 10A5o2n4t => Output : " + runLengthDecoding("10A5o2n4t"));
 System.out.println("Input: 10AA5o2n4t => Output : " + runLengthDecoding("10AA5o2n4t"));
 System.out.println("Input: A5o => Output : " + runLengthDecoding("A5o"));
 System.out.println("Input: AB5o => Output : " + runLengthDecoding("AB5o"));
 

 public static String runLengthDecoding(String str3) 
 String convert = "";
 int number = 0;
 String numberString = "";
 String toBeRepeatedString = "";
 boolean flag = false;
 for (int i = 0; i <= str3.length() - 1; i++) 
 char currentChar = str3.charAt(i);
 if (Character.isDigit(currentChar)) // true or false, the current character is a digit
 numberString = numberString + currentChar; // store the possible integer
 else 
 if (i + 1 < str3.length()) 
 char nextChar = str3.charAt(i + 1); // check if the next char is a digit
 if (!Character.isDigit(nextChar)) else 
 flag = true;
 
 

 if (flag) 
 toBeRepeatedString += currentChar;

 // This will accomodate inputs "A3B";
 if (!numberString.isEmpty()) 
 number = Integer.parseInt(numberString); // parse the number of repeats
 else 
 number = 1;
 

 numberString = ""; // reset number

 String temp2 = "";

 // Repeat the currentChar
 for (int j = 0; j < number; j++) 
 temp2 += toBeRepeatedString;
 

 convert = convert + temp2; // store it to the result
 toBeRepeatedString = ""; // reset toBeRepeatedString
 

 

 
 return convert;
 

Result:

Input: 3A5o2n4t => Output : AAAooooonntttt
Input: 3AA5o2n4t => Output : AAAAAAooooonntttt
Input: 10A5o2n4t => Output : AAAAAAAAAAooooonntttt
Input: 10AA5o2n4t => Output : AAAAAAAAAAAAAAAAAAAAooooonntttt
Input: A5o => Output : Aooooo
Input: AB5o => Output : ABooooo

Here is the best way of doing the above problem it will handle all your scenarios:

public static void main(String[] args) 
 String input = "5a2s3T66e";
 System.out.println("Input is: "+input+" and output is: "+expandingCondenseString(input));

private static String expandingCondenseString(String input)
 StringBuilder result = new StringBuilder();
 String size = "";
 String value = "";
 for (int i=0;i<input.length();i++)
 if (Character.isDigit(input.charAt(i))) 
 size = size + input.charAt(i);
 else 
 value = value + input.charAt(i);
 if(i+1<input.length() && !Character.isDigit(input.charAt(i+1)))
 continue;
 
 if(size.isEmpty())
 size = "1";
 
 for (int j=0;j<Integer.parseInt(size);j++)
 result.append(value);
 
 size = "";
 value = "";
 
 
 return String.valueOf(result);