In Java how does one turn a String into a char or a char into a String?

char firstLetter = someString.charAt(0);
String oneLetter = String.valueOf(someChar);

You find the documentation by identifying the classes likely to be involved. Here, candidates are java.lang.String and java.lang.Character.

You should start by familiarizing yourself with:

• Primitive wrappers in java.lang
• Java Collection framework in java.util

It also helps to get introduced to the API more slowly through tutorials.

• Manipulating characters in a String