FridaTveit 2754bec3ae grep: add exercise (#1429) | 6 лет назад | |
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Search a file for lines matching a regular expression pattern. Return the line number and contents of each matching line.
The Unix grep
command can be used to search for lines in one or more files
that match a user-provided search query (known as the pattern).
The grep
command takes three arguments:
Your task is to implement the grep
function, which should read the contents
of the specified files, find the lines that match the specified pattern
and then output those lines as a single string. Note that the lines should
be output in the order in which they were found, with the first matching line
in the first file being output first.
As an example, suppose there is a file named "input.txt" with the following contents:
hello
world
hello again
If we were to call grep "hello" input.txt
, the returned string should be:
hello
hello again
As said earlier, the grep
command should also support the following flags:
-n
Print the line numbers of each matching line.-l
Print only the names of files that contain at least one matching line.-i
Match line using a case-insensitive comparison.-v
Invert the program -- collect all lines that fail to match the pattern.-x
Only match entire lines, instead of lines that contain a match.If we run grep -n "hello" input.txt
, the -n
flag will require the matching
lines to be prefixed with its line number:
1:hello
3:hello again
And if we run grep -i "HELLO" input.txt
, we'll do a case-insensitive match,
and the output will be:
hello
hello again
The grep
command should support multiple flags at once.
For example, running grep -l -v "hello" file1.txt file2.txt
should
print the names of files that do not contain the string "hello".
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\ExerciseClassNameTest.java:14: 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 ExerciseClassName.java
.
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!
You can run all the tests for an exercise by entering
$ gradle test
in your terminal.
Conversation with Nate Foster. http://www.cs.cornell.edu/Courses/cs3110/2014sp/hw/0/ps0.pdf
It's possible to submit an incomplete solution so you can see how others have completed the exercise.