Video Materials

To start this course, we have looked into strings. They are a very natural way to represent data, especially in real world applications. Often though, the datapoints can be very large and require multiple modifications. We also examined how strings work: element access, retrieving the size, and modifying them. We looked into some alternatives which included StringBuilders for Java and character arrays for Python.

To really understand this point, we have included a comparison. We have implemented the APPENDER and APPENDER_LIST functions in both Python and Java. For the Java implementation, we utilized StringBuilders.

1. function APPENDER(NUMBER, BASE)
2.     RESULT = ""
3.     loop I from 1 to NUMBER
4.         RESULT = RESULT + BASE
5.         if I MOD 2 = 0
6.             RESULT = RESULT + " "
7.         else
8.             RESULT = RESULT + ", " 
9.     end loop
10.    return RESULT
11. end function
1. function APPENDER_LIST(NUMBER, BASE)
2.     RESULT = []
3.     loop I from 1 to NUMBER
4.         RESULT.APPEND(BASE) 
5.         if I MOD 2 = 0
6.             RESULT.APPEND(" ") 
7.         else
8.             RESULT.APPEND(", ")  
9.     end loop
10.    RESULT = "".JOIN(RESULT)
11.    return RESULT
12. end function
Info

For the tests of 108 and 109 in Java, the string implementation took over 24 hours and the StringBuilder implementation ran out of memory. For these reasons, they are omitted from the figure.

Python Time Python Time Java Time Java Time

These figures compare Strings and lists for Python and Strings and StringBuilders for Java. The intention of these is not to compare Python and Java.

In both languages, we see that the string function and the respective alternative performed comparably until approximately 106 (1,000,000 characters). Again, these are somewhat contrived examples with the intention of understanding side effects of using strings.

As we have discussed, modern coding languages will have clean up protocols and memory management strategies. With the intention of this class in mind, we will not discuss the memory analysis in practice.

When modifying strings we need to be cognizant of how often we will be making changes and how large those changes will be. If we are just accessing particular elements or only doing a few modifications then using plain strings is a reasonable solution. However, if we are looking to build our own DNA sequence this is not a good way to go as strings are immutable.