Java中的模式/数组问题

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]);
            }
        }
    }
}

Answer 1

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?

Answer 2

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

<=必须为<因为您从0开始并且有10个项目，所以i必须从0到9。

Answer 3

Try

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

and you'll be fine :)

Answer 4

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 <=

Answer 5

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++;
            }
        }
    }
}