Please help with this as i do not understand how to accomplish the code in java

i have to write an algorithm that gets an expression as a String in prefix notation and returns a String with the expression in postfix notation. For example, on input / * 2 + 3 4 - 18 16 the method returns 2 3 4 + * 18 16 - /. we can assume input is always valid

so can someone implement this function for the question

public string prefix2post(string prefix){

}

help would be appreciated pls