Word Count
Word Count

Word Count



You teach English as a foreign language to high school students.

You've decided to base your entire curriculum on TV shows. You need to analyze which words are used, and how often they're repeated.

This will let you choose the simplest shows to start with, and to gradually increase the difficulty as time passes.


Your task is to count how many times each word occurs in a subtitle of a drama.

The subtitles from these dramas use only ASCII characters.

The characters often speak in casual English, using contractions like they're or it's. Though these contractions come from two words (e.g. we are), the contraction (we're) is considered a single word.

Words can be separated by any form of punctuation (e.g. ":", "!", or "?") or whitespace (e.g. "\t", "\n", or " "). The only punctuation that does not separate words is the apostrophe in contractions.

Numbers are considered words. If the subtitles say It costs 100 dollars. then 100 will be its own word.

Words are case insensitive. For example, the word you occurs three times in the following sentence:

You come back, you hear me? DO YOU HEAR ME?

The ordering of the word counts in the results doesn't matter.

Here's an example that incorporates several of the elements discussed above:

  • simple words
  • contractions
  • numbers
  • case insensitive words
  • punctuation (including apostrophes) to separate words
  • different forms of whitespace to separate words

"That's the password: 'PASSWORD 123'!", cried the Special Agent.\nSo I fled.

The mapping for this subtitle would be:

123: 1
agent: 1
cried: 1
fled: 1
i: 1
password: 2
so: 1
special: 1
that's: 1
the: 2

Since this exercise has difficulty 5 it doesn't come with any starter implementation. This is so that you get to practice creating classes and methods which is an important part of programming in Java. It does mean that when you first try to run the tests, they won't compile. They will give you an error similar to:

 path-to-exercism-dir\exercism\java\name-of-exercise\src\test\java\ error: cannot find symbol
        ExerciseClassName exerciseClassName = new ExerciseClassName();
 symbol:   class ExerciseClassName
 location: class ExerciseClassNameTest

This error occurs because the test refers to a class that hasn't been created yet (ExerciseClassName). To resolve the error you need to add a file matching the class name in the error to the src/main/java directory. For example, for the error above you would add a file called

When you try to run the tests again you will get slightly different errors. You might get an error similar to:

  constructor ExerciseClassName in class ExerciseClassName cannot be applied to given types;
        ExerciseClassName exerciseClassName = new ExerciseClassName("some argument");
  required: no arguments
  found: String
  reason: actual and formal argument lists differ in length

This error means that you need to add a constructor to your new class. If you don't add a constructor, Java will add a default one for you. This default constructor takes no arguments. So if the tests expect your class to have a constructor which takes arguments, then you need to create this constructor yourself. In the example above you could add:

ExerciseClassName(String input) {


That should make the error go away, though you might need to add some more code to your constructor to make the test pass!

You might also get an error similar to:

  error: cannot find symbol
        assertEquals(expectedOutput, exerciseClassName.someMethod());
  symbol:   method someMethod()
  location: variable exerciseClassName of type ExerciseClassName

This error means that you need to add a method called someMethod to your new class. In the example above you would add:

String someMethod() {
  return "";

Make sure the return type matches what the test is expecting. You can find out which return type it should have by looking at the type of object it's being compared to in the tests. Or you could set your method to return some random type (e.g. void), and run the tests again. The new error should tell you which type it's expecting.

After having resolved these errors you should be ready to start making the tests pass!


This is a classic toy problem, but we were reminded of it by seeing it in the Go Tour.
Last updated 25 May 2023
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