CodeGym/Help with Java Tasks/I don't understand

Level 15

Sugar Hill

06.10.2019
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26comments

I don't understand

Question about the task

Functionality is not enough!

Java Syntax, Level 10, Lesson 11

Resolved

It says the value should not be lost and displayed but that is what happens.

Task: The program reads a pair (a number and string) from the keyboard and displays it on the screen.
New task: The program reads pairs (a number and string) from the keyboard and stores them in a HashMap.
Any empty input signifies the end of data entry.
The numbers can be repeated.
The strings are always unique.
The entered data must not be lost!
The program then displays the contents of the HashMap on the screen.
Each pair on a new line.

Example input:
1 Sam 2 I 1 Am

Example output:
1 Sam 2 I 1 Am

Requirements:

The program must read data from the keyboard.
The program should display text on the screen.
In the main method, declare a HashMap variable and immediately initialize it.
The program should put the pairs read from the keyboard into the HashMap.
The program should display the contents of the HashMap in accordance with the conditions. The key and value are separated by a space. Each value should be on a new line.

package com.codegym.task.task10.task1019; import java.io.*; import java.util.*; /* Functionality is not enough! */ public class Solution { public static void main(String[] args) throws IOException { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); HashMap<String,Integer> map = new HashMap<>(); while(true) { Integer id = Integer.parseInt(reader.readLine()); if(id == 0) break; String name = reader.readLine(); if(name.isEmpty() && !(id == 0)){ map.put(name,id); break; }else if(name.isEmpty()) break; } for(Map.Entry<String,Integer> entry : map.entrySet()){ System.out.println(entry.getValue()+" "+entry.getKey()); } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

7 October 2019, 13:20

It says to stop accepting input when a blank value is entered. At line 17 you have a condition to break the loop if the entered number is '0', but '0' is valid integer and not a blank value. At line 22: if(name.isEmpty() && !(id == 0)){ the highlighted part it unnecessary as you already made the check at line 17. If line 17 is true then the loop will break and line 22 would never be reached, which means that if line 22 is reached you already know that id does not equal what line 17 checks for.

Yash

Level 15 , Sugar Hill, United States

10 October 2019, 01:10

So I should change 0 to null?

Guadalupe Gagnon

Level 37 , Tampa, United States

10 October 2019, 01:28

line 16 will throw an exception if you try parsing a null or empty value. I would check for a blank string before trying to parse and break the loop if the entered string is empty.

Yash

Level 15 , Sugar Hill, United States

11 October 2019, 15:10

I changed it to something like this,

public class Solution {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        HashMap<String, Integer> map = new HashMap<>();
        String name = "";
        Integer id = null;
        boolean b = true;
        while (b) {
            int i = 0;

            for (i = 0; i < 2; i++) {
                if (reader.readLine() == "") {
                    b = false;
                }
                else {
                    try {
                        id = Integer.parseInt(reader.readLine());
                    }

                    catch (NumberFormatException e) {
                        name = reader.readLine();
                    }
                }
            }

            if (name.isEmpty() && !(id == null)) {
                map.put("", id);
                break;
            } else if (name.isEmpty()) {
                break;
            }
            else if (!(name == "") && !(id == null)){
                map.put(name,id);
            }
        }
        for (Map.Entry<String, Integer> entry : map.entrySet()) {

            System.out.println(entry.getValue() + " " + entry.getKey());
        }

    }
}

still having issues. Null pointer exception on line 36.

Yash

Level 15 , Sugar Hill, United States

11 October 2019, 15:26

fixed exception by changing .isEmpty() to == "". But I have infinite loop.

Guadalupe Gagnon

Level 37 , Tampa, United States

11 October 2019, 16:54

solution

There is a lot going on in the code that you shared. I would go back to the code you started with (the code attached to this post), it is closer to solving this. The problem with that code is your first readline() at line 16 should be saved as a string, not as an int. Then you should check if that string contains a value and break the loop if it does not. After you confirm that it contains a value then you can parse to an int and read a second value in. Here is an outline of how the code should look inside that loop:

while(true) {
   // read in a string and save in a variable, lets say x

   // if variable x is empty then break

   // parse x to an int  (int id = Integer.parseInt(x))

   // read in a second string and save to a variable, name

    // if variable name is empty then break

    // put name and id in the HashMap
}

. Don't over think things.

Yash

Level 15 , Sugar Hill, United States

13 October 2019, 20:07

Thank you. One last question. Does the order of output affect the verification? I have the right output but the order it came out was unexpected and the verification failed. input : 1 String1 2 String2 3 String3 4 String4 4 String5 7 String6 7 String7 8 String8 9 String9 10 String10 output : 9 String9 8 String8 10 String10 7 String7 7 String6 4 String5 4 String4 3 String3 2 String2 1 String1

Guadalupe Gagnon

Level 37 , Tampa, United States

13 October 2019, 21:12

Hash maps don't guarantee the output to be exactly how it is input when iterating over the values. Because of this, the output order should not affect the verification. If you are still failing there may be another issue.

Yash

Level 15 , Sugar Hill, United States

14 October 2019, 19:14

I’m still failing, is the output correct?

Guadalupe Gagnon

Level 37 , Tampa, United States

14 October 2019, 19:46

It looks correct, what is your code now?

Yash

Level 15 , Sugar Hill, United States

14 October 2019, 21:53

This is the while loop, everything else is same

while(true) {
          String s = reader.readLine();

          if (s == null){
              break;
          }

          int id = Integer.parseInt(s);

          String name = reader.readLine();

          if (name.isEmpty()){
              break;
          }

          map.put(name,id);
        }

Guadalupe Gagnon

Level 37 , Tampa, United States

15 October 2019, 13:21

reader.readline() doesn't return null values, if no input is entered then it will return an empty string. There are 2 different ways to properly check for this: .isEmpty() and isBlank(). The differences between those are: isEmpty() checks only if the returned string equals "", any other string including one with only spaces will fail this check isBlank() checks the string for valid characters that are not empty space, so "" will pass as well as " " (this is a string of blank spaces). So, at line 4: try s.isBlank() because you do not want to parse an empty string that could have spaces, and if that does not work try that at line 12 too.

Yash

Level 15 , Sugar Hill, United States

15 October 2019, 22:21

.isEmpty() throws a NullPointerException. .isBlank() sends a compiler error "cannot find symbol method 'isBlank()'."(isBlank() only java 11 feature maybe codegym not updated to java 11)

Guadalupe Gagnon

Level 37 , Tampa, United States

16 October 2019, 00:16

are you using intelliJ?

Yash

Level 15 , Sugar Hill, United States

16 October 2019, 20:12

I tried IntelliJ and codegym website

Guadalupe Gagnon

Level 37 , Tampa, United States

16 October 2019, 20:34

isempty() won't throw a null pointer exception in intellij, this should pass the task for you:

while(true) {
          String s = reader.readLine();

          if(s.equals("")) { //or s.isEmpty()
              break;
          }

          int id = Integer.parseInt(s);

          String name = reader.readLine();

          if (name.equals("")){/or name.isEmpty()
              break;
          }

          map.put(name,id);
}

Yash

Level 15 , Sugar Hill, United States

17 October 2019, 00:28

didn't pass. Threw NullPointerException.

Guadalupe Gagnon

Level 37 , Tampa, United States

17 October 2019, 02:29

need your full code, there is nothing in that loop that would result in null

Yash

Level 15 , Sugar Hill, United States

17 October 2019, 21:01

package com.codegym.task.task10.task1019;

import java.io.*;
import java.util.*;

/*
Functionality is not enough!

*/

public class Solution {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        HashMap<String,Integer> map = new HashMap<>();
        while(true) {
            String s = reader.readLine();

            if(s.isEmpty()) { //or s.isEmpty()
                break;
            }

            int id = Integer.parseInt(s);

            String name = reader.readLine();

            if (name.isEmpty()){
                break;
            }

            map.put(name,id);
        }
        for(Map.Entry<String,Integer> entry : map.entrySet()){
            System.out.println(entry.getValue()+" "+entry.getKey());
        }
    }
}

Guadalupe Gagnon

Level 37 , Tampa, United States

18 October 2019, 14:02

Time to tinker until verification passes. try removing lines 26-28 try:

String s = "";
s = reader.readLine();

try resetting the task. You can copy your code first then paste it back in. Hopefully one of those will allow verification, and if it does let us know which one.

Yash

Level 15 , Sugar Hill, United States

18 October 2019, 23:06

I think there is another issue. If I enter an extra number without a string it prints out null.

Yash

Level 15 , Sugar Hill, United States

18 October 2019, 23:09

Also if I do your tip of declaring a as null, it throws a number format exception : null.

Yash

Level 15 , Sugar Hill, United States

18 October 2019, 23:11

solution

Did it 47 attempts

public class Solution {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        HashMap<String,Integer> map = new HashMap<>();
        while(true) {
            int id;
            String s = "";
            s = reader.readLine();

            if(s == ""){ //or s.isEmpty()
                break;
            }

            try {
            id = Integer.parseInt(s);
            }

            catch (NumberFormatException e){
                break;
            }
            String name = "";
            name = reader.readLine();

            if (name == ""){
                break;
            }

            map.put(name,id);
        }
        for(Map.Entry<String,Integer> entry : map.entrySet()){
            System.out.println(entry.getValue()+" "+entry.getKey());
        }
    }
}

I wrote a try-catch statement for the NumberFormatException and if it catches the exception it breaks the loop.

MaGaby2280

Level 41 , Guatemala City, Guatemala

12 November 2019, 19:10

If it helps you, this is how I solved it, after 16 attempts: public class Solution { public static void main(String[] args) throws IOException { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); HashMap<String, Integer> map = new HashMap<String, Integer>(); String name; Integer num; while(true) { String s = reader.readLine(); if(s.isEmpty()) break; num = Integer.parseInt(s); name = reader.readLine(); if(!map.containsValue(name)) map.put(name, num); } for(Map.Entry<String, Integer> pair : map.entrySet()) { System.out.println(pair.getValue() + " " + pair.getKey()); } } }

hidden #10426208

Level 11

12 January 2020, 11:16

well done yash, even i got frustated with this task, it took 19 attempts and hours.

Thomas Sixberry

Level 16 , Rochester Hills, United States

5 February 2020, 03:24

The code you entered here pulls up String 8 first. It kind of baffles me why this is a good and verifiable code.