Pattern/Array issue in java

Question

I am studying for an upcoming test next month and looking at some basic problems. This one is a program that requires entering a few sentences and reprinting any that contain a certain string, 'pattern' in this case.

My attempt is below and it compiles however I receive the following error when trying to run it:

   Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 10
at Grep.main(Grep.java:18)

import java.util.Scanner;
import java.io.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

class Grep {

    public static void main(String[] args) {

        Pattern pattern = Pattern.compile("[Pp]attern");
        String sentences[] = new String[10];
        Scanner scanner = new Scanner(System.in); 

        System.out.println("Please enter some sentences: ");

        for (int i = 0; i <= sentences.length; i++) {
            String s = scanner.next(); 
            sentences[i] = s;
        }

        for (int i = 0; i < sentences.length; i++) { 
            Matcher matcher = pattern.matcher(sentences[i]);
            while (matcher.find()) {
                System.out.println(sentences[i]);
            }
        }
    }
}

John3136 · Accepted Answer · 2012-08-02 05:27:55Z

3

for (int i = 0; i <= sentences.length; i++) {

How many items are in the array? What is the last index? What is the last index your loop uses? How many sentances in total does your loop access?

answered Aug 2, 2012 at 5:27

John3136

29.3k4 gold badges55 silver badges77 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

gmustudent · Accepted Answer · 2012-08-03 02:33:43Z

Try this. It works.

Tips: Make sure you use nextLine() so that the input will read full sentences. And I switched your while loop for an if statement within the for loop. No need for two loops there. And I also condensed your first for loop to just one line. No need to create a string variable if you only need it for a second. Just skip that step entirely and get to the point! Good luck, Hope this helps!

Below Is A Program That Mirrors Yours But Now Works

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Grep 
{
    public static void main(String[] args) 
    {
        Pattern pattern = Pattern.compile("[Pp]attern");
        String sentences[] = new String[3];
        Scanner scanner = new Scanner(System.in);

        System.out.println("Please enter some sentences: ");

        for (int i = 0; i < sentences.length; i++) 
            sentences[i] = scanner.nextLine();

        for (int i = 0; i < sentences.length; i++) 
        { 
            Matcher matcher = pattern.matcher(sentences[i]);
            if (matcher.find()) 
                System.out.println(sentences[i]);
        }
    }
}

Below Is How I Would Write This Same Program. Comments Included For Clarification

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Grep 
{
    public static void main(String[] args) 
    {
        // Initialize and Declare Variables
        Pattern pattern = Pattern.compile("[Pp]attern");
        String sentences[] = new String[3];
        Scanner scanner = new Scanner(System.in);
        int foundCount = 1;


        // Present A Title For The End User
        System.out.println("This Program Will Catch Sentences With The Term Pattern.\n");


        // Read The Inputs From The Users
        for (int i = 0; i < sentences.length; i++)
        {
            System.out.print("Enter Sentence #" + (i+1) + ":  ");
            sentences[i] = scanner.nextLine();
        }


        // Line Break
        System.out.println();


        // Write Sentences That Include The Term Pattern
        for (int i = 0; i < sentences.length; i++) 
        { 
            Matcher matcher = pattern.matcher(sentences[i]);
            if (matcher.find())
            {
                System.out.println(foundCount + ")  " + sentences[i]);
                foundCount++;
            }
        }
    }
}

Thank you very much for your help. Any tips on how I would invoke the search term from the command line? Eg if I wanted to search for pattern in the input and invoked 'java Grep pattern'.

Jon Lin · Accepted Answer · 2012-08-02 05:28:08Z

0

for (int i = 0; i <= sentences.length; i++) {

The <= needs to be < because you are starting from 0 and you have 10 items, so i has to go from 0 to 9.

answered Aug 2, 2012 at 5:28

Jon Lin

144k29 gold badges226 silver badges224 bronze badges

1 Comment

BLL27 Over a year ago

Awesome, completely missed that. Thank you.

Harmeet Singh · Accepted Answer · 2012-08-02 05:33:02Z

0

The problem is in line :18 of your code which is for (int i = 0; i <= sentences.length; i++) it should be for (int i = 0; i < sentences.length; i++)

as you your own in the next for loop in your code has used < instead of <=

answered Aug 2, 2012 at 5:33

Harmeet Singh

2,61619 silver badges21 bronze badges

1 Comment

Adriaan Koster Over a year ago

Java generally uses 0-based indexes, so the last element will be at position (size - 1).

sloth · Accepted Answer · 2012-08-02 14:21:49Z

0

Try

for (int i = 0; i < sentences.length; i++)

and you'll be fine :)

edited Aug 2, 2012 at 14:21

sloth

101k21 gold badges182 silver badges224 bronze badges

answered Aug 2, 2012 at 5:29

Mark Bramnik

42.9k5 gold badges67 silver badges111 bronze badges

1 Comment

BLL27 Over a year ago

Awesome, completely missed that. Thank you.

Collectives™ on Stack Overflow

Pattern/Array issue in java

5 Answers 5

Comments

1 Comment

1 Comment

1 Comment

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

Comments

1 Comment

1 Comment

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related