java - Loop Keyword Program Homework

Question

It will ask the user for a keyword to search for. Then, it will ask the user to enter sentences over and over. The user can stop the process by typing “stop” instead of a sentence (which means, of course, that we can’t analyze the one word sentence ‘stop’, but that is OK). Once the user has finished entering the sentences, the program should display the following statistics:

1. The total number of sentences entered
2. The total number of sentences that contain the keyword
3. The average starting position of the keyword in the sentences that contain the keyword.

Can somebody help me put this program together? For #3 we only do average position of the sentences that contain the keyword.

I have the loop part, and for #3 I'm guessing we would use indexOf. #2 inputString.contains(keyword) I'm guessing? Can somebody help me with 1-3 and putting them into a Java program? Thanks.

import java.util.Scanner;

public class Lab6Loops {

    public static void main(String[] args)  {

        String keywordString;
        String inputString;
        Scanner keyboard = new Scanner (System.in);
        int numofSentences = 0;
        int numofKeyword = 0;                       
        System.out.println ("Enter a keyword. We will search each sentence for this word.");
        keywordString = keyboard.nextLine ();
        System.out.println ("Please enter a sentence or type 'stop' to finish");
        inputString = keyboard.nextLine ();
        while( !inputString.equals ("stop"))
        {       
            if(inputString.contains (inputString));
            numofSentences = numofSentences + 1;
            if(inputString.contains (keywordString));
            numofKeyword = numofKeyword + 1;
            System.out.println ("Enter a line of text or 'stop' to finish");
            inputString = keyboard.nextLine();
        }
        System.out.println ("You entered " + numofSentences + " sentences");
        System.out.println ("You have " + numofKeyword + "sentences that contain the keyword");
    }   
}

Answer 1

I like having self-documenting code, so here are a couple suggestions for how you can have a nice tight main loop:

functional-ish semantics

public void loop() {
  // TODO: ask for the keyword and store it somewhere

  while(true) {
    try {
      updateStatistics(checkOutput(getSentence()));
    } catch (EndOfInput) {
      printStatistics();
    }
  }
}

Object-Oriented

public void loop() {
  String keyword = myPrompter.getNextSentence();
  myAnalyzer.setKeyword(keyword);

  while (true) {
    String sentence = myPrompter.getNextSentence();
    AnalysisResult result = myAnalyzer.analyze(sentence);
    if (result.isEndOfInput()) {
      myAnalyzer.printStatistics();
      return;
    }
  }
}

What both of these approaches gives you is a simple framework to plug in the specific logic. You could do all of it inside the main loop, but that can get confusing. Instead, it's preferable to have one function doing one task. One function runs the loop, another gets the input, another counts the # of sentences, etc.

Sometimes I'll start with those little functions, and build the app from the bottom-up, so I'd write a method that takes a string and returns true/false depending on if it's the string "stop". You can even write unit tests for that method, so that when you're building the rest of the app, you know that method does what you intended it to. It's nice to have lots of modular components that you can test along the way, rather than writing a huge long loop and wondering why it's not doing what you want.