Emulates Java's StringBuilder and StringJoiner, sort of.

stringutils.py

class StringBuilder:
    """
        Works like Java's StringBuilder
    """
    def __init__(self, initial_string=None):
        if initial_string is not None:
            self.string = initial_string
        else:
            self.string = ""
    def append(self, string):
        self.string += string

    def toString(self):
        return self.string
    def clear(self):
        self.string = ""

    
class StringJoiner(StringBuilder):
    """
        Works like Java's StringJoiner
    """
    def __init__(self, delimiter):
        self.delimiter = delimiter
        super(StringJoiner, self).__init__()

    def append(self, string):
        if self.string != "":
            self.string += self.delimiter + string
        else:
            self.string += string
    def clear(self):
        self.string = ""


# Usage
sb = StringBuilder()
sb.append("Hello, ")
sb.append("World!")
assert sb.toString() == "Hello, World!"

sj = StringJoiner(", ")
sj.append("a")
sj.append("b")
sj.append("c")
assert sj.toString() == "a, b, c"