Create a class with public static methods, then you can call them every where with ClassName.methodName(parameters):
public class Util {
public static String methodOne(String param) {
//do something
return param;
}
public static String methodTwo(String param) {
//do something
return param;
}
//...
}
Inside other classes:
String someString = Util.methodOne("Some String");
// ...