Accepting input forever?

Question about the task

Duplicating words

Java Syntax, Level 7, Lesson 9

Under discussion

My code just seems to accept input strings forever, and I cannot for the life of me figure out why. Can someone help?

1. Read 10 words from the keyboard and add them to a list of strings.

2. The doubleValues method should duplicate words like this:
alpha, beta, gamma, -> alpha, alpha, beta, beta, gamma, gamma.

3. Display the result, each value on a new line.

Requirements:

Declare a string list variable and immediately initialize it.
Read 10 lines from the keyboard and add them to the list.
The doubleValues method should duplicate list elements like this: alpha, beta, gamma, -> alpha, alpha, beta, beta, gamma, gamma.
Display the resulting list, each element on a new line.

package com.codegym.task.task07.task0717; import java.io.BufferedReader; import java.io.InputStreamReader; import java.util.ArrayList; /* Duplicating words */ public class Solution { public static void main(String[] args) throws Exception { // Read strings from the console and declare an ArrayList here ArrayList<String> list = new ArrayList<String>(); BufferedReader read = new BufferedReader(new InputStreamReader(System.in)); for (int i = 0; i < 10; i++) { list.add(read.readLine()); } ArrayList<String> result = doubleValues(list); // Display result System.out.println(result); } public static ArrayList<String> doubleValues(ArrayList<String> list) { //write your code here ArrayList<String> oper = list; for (int i = 0; i < list.size(); i++) { oper.add(i, list.get(i)); } return oper; } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

22 September 2020, 20:46

It actually isn't accepting values past line 19, you can add an output line following that to see this:

BufferedReader read = new BufferedReader(new InputStreamReader(System.in));
for (int i = 0; i < 10; i++) {
   list.add(read.readLine());
}  // line 19
System.out.println("Input loop completed"); //<< add this line
ArrayList<String> result = doubleValues(list);

And when you enter 10 values that output line will be run. The problem with this code is the infinite loop at line 29-31. When there is an infinite loop you can still type in the cmd window, just the program doesn't do anything with those inputs. If you let the program run for a little bit, maybe 15-30 seconds depending on your computer, the code will generate an OutOfMemoryError and exit. Just like I added a of output after line 19, I would highly recommend that you start doing this in all your code to check that it is working as intended. You can use it to output values or equations, alert when lines have been reached, check the values contained in a list etc. It is one of the first methods used to debug programs.